Glyphosate pathways to modern diseases V: Amino acid analogue …amsi.ge/jbpc/11616/03SA16A.pdf ·...

© 2016 Collegium Basilea & AMSIdoi: 10.4024/03SA16A.jbpc.16.01

Journal of Biological Physics and Chemistry 16 (2016) 9–46Received 2 February 2016; accepted 31 March 2016 9

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1. INTRODUCTION

While it might be expected that fidelity is always perfectin mapping from the DNA triple code to the specificamino acid it codes for, multiple studies have shown thatthis is not the case [1–5]. In addition to coding errorsleading to substitution of another core amino acid, thereexist hundreds of non-protein amino acids that could besubstituted, some of which occur naturally in plants [1, 2].Others are produced as oxidation products of the originalamino acids [3]. In inflammatory conditions such asAlzheimer’s disease, atherosclerosis and cataractgeneration, accumulation of oxidized proteins ascomponents of lipofuscin are believed to contribute to thedisease process [6]. Remarkably, oxidized amino acidscan be directly incorporated into protein chains throughprotein synthesis [4]. These damaged peptides cannot berepaired except through complete enzymatic hydrolysis,and their accumulation with aging is believed to disruptcellular functions.

Finally, and most significantly, multiple syntheticallyproduced amino acids, close structural analogues of

natural amino acids, can be mistakenly incorporated intopeptides [7, 3]. There are 20 unique aminoacyl-tRNAsynthetases in the ribosomal system, each of whichspecifically recognizes one amino acid, according to theDNA code. Ominously, there does not appear to be anyproof-reading mechanism for the ribosomal system.Once an amino acid analogue fools the recognitionprocess, there is no mechanism to abort translation anddiscard an erroneously produced peptide sequence [4]. Adirect quote from Rodgers et al. [4] makes this veryclear: “Certain structural analogues of the protein aminoacids can escape detection by the cellular machinery forprotein synthesis and become misincorporated into thegrowing polypeptide chain of proteins to generate non-native proteins.” Glyphosate is a glycine molecule with amethyl-phosphonyl group bound to the nitrogen atom. Asan analogue of glycine, it can be expected to displaceglycine at random points in the protein synthesis process,with unknown consequences.

Godballe et al. describe in their 2011 paper howglycine can be used to construct synthetic molecules

Glyphosate pathways to modern diseases V: Amino acid analogue of glycine indiverse proteins

Anthony Samsel1, * and Stephanie Seneff 2, **

1 Research Scientist, Deerfield, NH 03037, USA2 Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge, MA 02139, USA

Glyphosate, a synthetic amino acid and analogue of glycine, is the most widely used biocideon the planet. Its presence in food for human consumption and animal feed is ubiquitous.Epidemiological studies have revealed a strong correlation between the increasing incidencein the United States of a large number of chronic diseases and the increased use ofglyphosate herbicide on corn, soy and wheat crops. Glyphosate, acting as a glycineanalogue, may be mistakenly incorporated into peptides during protein synthesis. A deepsearch of the research literature has revealed a number of protein classes that depend onconserved glycine residues for proper function. Glycine, the smallest amino acid, has uniqueproperties that support flexibility and the ability to anchor to the plasma membrane or thecytoskeleton. Glyphosate substitution for conserved glycines can easily explain a link withdiabetes, obesity, asthma, chronic obstructive pulmonary disease (COPD), pulmonaryedema, adrenal insufficiency, hypothyroidism, Alzheimer’s disease, amyotrophic lateralsclerosis (ALS), Parkinson’s disease, prion diseases, lupus, mitochondrial disease, non-Hodgkin’s lymphoma, neural tube defects, infertility, hypertension, glaucoma, osteoporosis,fatty liver disease and kidney failure. The correlation data together with the direct biologicalevidence make a compelling case for glyphosate action as a glycine analogue to account formuch of glyphosate’s toxicity. Glufosinate, an analogue of glutamate, likely exhibits ananalogous toxicity mechanism. There is an urgent need to find an effective and economicalway to grow crops without the use of glyphosate and glufosinate as herbicides.

* Email: [email protected]* * Corresponding author: S. Seneff, Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of

Technology, USA; e-mail: [email protected]

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having functionality resembling the activities of cationicantimicrobial peptides [8]. A reactive side chain is attachedto the nitrogen of glycine, and such units can be assembledinto “peptoid” chains that in many ways resemble peptidechains, except that they are highly resistant to proteolysis.This is presumed to be beneficial because it allows theantimicrobial agent to survive longer in the tissues. Theseauthors remarked: “N-substituted glycines can be viewedas amino acids, where the side chain is attached to theamine nitrogen instead of the α-carbon, and oligomers ofthese building blocks are called α-peptoids.”

Glyphosate, is in fact, an N-substituted glycine; i.e., apeptoid unit. If glyphosate is misincorporated into a peptideunder construction, it could interfere with the disassemblyof the defective peptide, leading to the accumulation ofundegraded short peptide chains with unknown conse-quences in the blood or in cells harbouring such defectiveproteins. It is intriguing and suggestive that phosphonylgroups are attractive as a component of designer peptidesthat inhibit proteases [9] and of potential insecticides thatwork by inhibiting protein degradation [10].

There is considerable evidence that glyphosate’sbiological effects are due in part to its action as a glycineanalogue. Glyphosate disrupts chlorophyll synthesis inplants, likely due in (large) part to its inhibition of δ-aminolevulinic acid (ALA) synthesis, the rate-limitingstep in the synthesis of the core pyrrole ring. It has beenproposed that this may be a major factor, besidesdisruption of the shikimate pathway, in its toxicity to plants[11]. Its action as a glycine analogue likely causescompetitive inhibition of ALA synthase from glycine andsuccinyl coenzyme A. Glyphosate has been shown toactivate NMDA receptors in rat hippocampus [12], andthis has been proposed to be in part due to glyphosate’sability to act as a ligand in place of glycine, in addition toglutamate (as the other ligand), whose overexpression isinduced by glyphosate [13]. Both glyphosate and itsmetabolite aminomethylphosphonic acid (AMPA) caninhibit the growth of some tumour cells, likely bysuppressing glycine synthesis [17].

If glyphosate substitutes for glycine in peptidesequences under construction, the results are likely to becatastrophic at multiple levels. The evidence thatglyphosate interferes with glycine’s rôles as a receptorligand and as a substrate, and also suppresses glycinesynthesis, implies that glyphosate could be taken upinstead of glycine and subsequently incorporated into apeptide during protein synthesis. Several examplesalready exist of non-coding amino acids causing harmthrough misincorporation into peptides. For example, anatural non-coding amino acid analogue of proline,azetidine-2-carboxylic acid (Aze), is linked to multiple

sclerosis due to its ability to displace proline in peptides[14]. Similarly, L-canavanine, a natural non-codinganalogue of L-arginine, is a toxin stored in the seeds ofcertain plants [15, 16]. β-N-methylamino-L-alanine(BMAA), a natural analogue of serine synthesized bycyanobacteria, is implicated in amyotrophic lateralsclerosis (ALS) and other neurological diseases [1]. Arecent study of glyphosate’s effects on the rhizospheremicrobiome showed sharp increases in the expression ofproteins involved with both protein synthesis andespecially protein degradation, implying that multiplesynthesized proteins were failing to fold properly and hadto be disassembled and reconstructed [18].

In this paper, we present a review of the literature ondiverse biologically important proteins that contain eitherglycine-rich regions or conserved/invariant glycineresidues. The evidence supports the likelihood thatmultiple diseases and conditions currently on the rise maybe caused by disruption of conserved glycine residues,often in ways that would be predicted on the basis ofglyphosate’s physical properties.

Glycine plays many important rôles in humanphysiology, as an inhibitory neurotransmitter, as substratefor the biosyntheses of glutathione, haem, creatine, nucleicacids and uric acid, and as a source for one-carbonmetabolism via the glycine cleavage system (GCS) [19].Glycine also plays an important rôle in metabolicregulation and as an antioxidant. Finally, and perhapsmost importantly, glycine is a highly conserved residue indiverse proteins, due to its unique properties. Glycine isthe smallest amino acid, having no side chains. It isespecially important in proteins that require flexibility, inhinge regions, or for ion gates that must open and closeunder varying circumstances [20]. Glycine is achiral, suchthat it can adopt angles representative of either L- or D-amino acids. Glycine confers flexibility through its uniqueability to adopt a wide range of main-chain dihedralangles [21]. Many highly conserved glycine residueshave been found in various proteins, reflecting this needfor flexibility and mobility. It has also been determinedempirically that substitution of conserved glycines in theenzyme acylphosphatase causes an increased tendencyto aggregate, and this may be an important considerationfor protection from the amyloid formation linked to manyneurological diseases [22].

Glycine plays a critical rôle in dimerization for anumber of protein classes for which dimerization is anessential step towards activation. Glycine is also highlyconserved as the terminal residue in certain peptides,where it often plays a crucial rôle by supporting binding tothe plasma membrane via myristoylation [23]. In manycases, even conservative substitution of alanine for

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glycine disrupts the enzyme’s function due toconformational changes following steric hindrance orimpaired myristoylation. Conserved glycine residues areoften located at the enzyme active site, particularly in theGXY or YXG motifs: glycine provides flexibilitynecessary to accommodate presence or absence of thesubstrate [24].

As of 2011, glyphosate was the largest sellingherbicide worldwide [25]. In a series of previouspublications [26–29], we have discussed howglyphosate’s known toxicological mechanisms can becausal in a large number of diseases whose incidence isgoing up in step with the steadily increasing use ofglyphosate on core corn, soy and wheat crops in the USA.The correlations between glyphosate usage and therecent alarming increase in multiple modern diseases arestunning, as presented in [30]. These include obesity,diabetes, end stage renal disease, renal failure, autism,Alzheimer’s disease, dementia, Parkinson’s disease,multiple sclerosis, intestinal infection, inflammatory boweldisease, stroke, leukemia, thyroid cancer, liver cancer,bladder cancer, pancreatic cancer and kidney cancer.Another study, looking at both human and animal data,revealed a large number of disorders of the newborn thatare increasing in step with glyphosate usage [31]. Theseinclude congenital heart disease, skin disorders,genitourinary disorders, blood disorders, metabolicdisorders and lung conditions. Our previous papers havebeen able to explain some of the pathology linked toglyphosate, predominantly through its powerful chelatingeffects, its adverse effects on beneficial gut microbes, itsinterference with the supply of crucial nutrients (in manycases derived from the shikimate pathway), and itssuppression of cytochrome P450 enzymes in the liver.

However, given the large number of diseases andconditions that are correlated with glyphosate usage, wesuspect that there is something much more insidious andfundamental than chelation or enzyme suppression that ishappening with glyphosate. The fact that it is a syntheticamino acid, an analogue of an amino acid that carriesmany important rôles in the function of proteinscontaining it, makes it conceivable that glyphosatesubstitution for glycine in peptides could cause a largenumber of adverse effects that would not otherwise beanticipated. This would explain how a single toxic agentcan be responsible for so many modern diseases.

2. BIOACCUMULATION, METABOLIZATION AND REACTIONPRODUCTS OF GLYPHOSATE

The ability of glyphosate to bioaccumulate and metabolizein vivo in animals was clearly demonstrated in a 1988study by Howe et al. [32]. Table 1 below outlines some ofthe study’s design features. Seven groups of rats receiveda single oral or intravenous (IV) 14C-radiolabeled dose ofglyphosate technical acid (N-phosphonomethyl glycine).Group 6 was preconditioned with unlabeled glyphosate at10 mg kg–1 day–1 for 14 days before receiving a singleradiolabeled dose. AMPA and N-methyl AMPA(MAMPA) were the main metabolites found in theexcreta, as well as other metabolites and reactionproducts. The fact that the research team found 0.3% ofthe dose as radioactive CO2 in the expired air from theanimals’ lungs, within 24 hours, demonstrated in vivometabolism. Glyphosate was the primary radiolabeledmaterial found in the urine and faeces; bioaccumulationwas found in all tissues, glands and organs. Additionaldetails can be found in previously published work [29].

Group No.

Dose/ mg kg–1 Animals Route

Duration/ days Samples collected

1 10 3 males 3 females Oral 7 Urine, faeces, expired air @ 6, 12, 24 h

2 10 3 males 3 females Oral 7 Blood @ 0.25, 0.5, 1, 2, 4, 6, 8, 12, 24, 48, 72, 120 and 168 h

7 10 3 males 3 females IV 7 ditto

3 10 5 males 5 females IV 7 Urine and faeces @ 6, 12, 24 h and daily thereafter; organs, tissues, carcass @ day 7

4 1000 5 males 5 females Oral 7 ditto

5 10 5 males 5 females Oral 7 ditto

6 10a 5 males 5 females Oral 7 ditto

Table 1. Glyphosate metabolism experimental design by Howe et al. [32].

a Group 6 was preconditioned with unlabeled glyphosate at 10 mg kg–1 day–1 for 14 days before receiving a single radiolabeled dose.


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Glyphosate metabolism by plants was alsoinvestigated by Dupont in 2007 [33]. Protection from theeffects of glyphosate was achieved through geneticengineering of maize plants to induce excess synthesis ofthe enzyme glyphosate acetyltransferase (GAT). Themodified gene, gat4601, produces the enzymeacetolactate synthase, which acetylates glyphosate, thuspreventing herbicide activity and plant death. N-acetylglyphosate (N-acetyl-N-phosphonomethyl glycine)is another amino acid and glycine analogue that wasfound in animals by Monsanto.

Acetylation does not preclude glyphosate’sincorporation as an amino acid. N-acetylglyphosate can berecycled back to glyphosate in vivo through deacetylation.This has been shown to occur in both goats [34] and

chickens [35]. The metabolization of N-acetylglyphosateincludes its decarboxylation to N-acetyl AMPA, andfurther metabolism to AMPA, as illustrated in Fig. 1.Radiolabeled metabolism of N-acetylglyphosate wasinvestigated in chickens [35], using orally dosed layinghens. Sacrificed hens, eggs and excreta were analysed/assayed for total 14C, glyphosate, AMPA, N-acetylgly-phosate and N-acetyl AMPA residues. Results areshown in Table 2. The fact that nearly 12% of the reactionproducts in egg yolk were recovered in the pepsin digest,and over 3% in the protease digest, suggests thatglyphosate is being incorporated into peptide chains. The14C radioactivity in the enzyme digests indicated that anadditional glyphosate analogue had been extracted;however, low residue levels precluded further analysis.

Figure 1. Glyphosate metabolism pathways.

a Total radioactive residue.b Equivalent value derived from liquid scintillation data.c Egg yolk and liver post-extraction solids (PES) were subjected to enzyme digestion.d Levels in reconstructed whole eggs calculated by summing (proportionally) residue levels in egg whites and yolks.e Not applicable.f Total recovery was derived by summing radioactivity in excreta, cage wash, egg yolks, egg whites and liver.

Table 2. 14C N-acetylglyphosate residues found in excreta, eggs and tissues (from Dupont, 2007 [35]).

Matrix TRRa Extracted Unextracted %dose mg/kg eqb %TRR mg/kg eq %TRR mg/kg eq

Egg white 0.01 0.02 94.3 0.01 5.7 < 0.01 Egg yolk 0.04 0.34 81.5 0.19 18.5 0.04c Whole egg 0.36d nae na Liver 0.05 0.51 95.6 0.48 4.4 0.02c Muscle 0.04 87.5 0.03 12.5


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Remarkably, in Dupont's study on goats [34], muscleextraction yielded only 42% of the total reactivity beforepepsin digest, and there was negligible additionalrecovery after both pepsin and protease digests. Thissuggests that glyphosate strongly inhibited the ability ofproteases to break down the proteins, as 58% remainedembedded and detectable only by its radioactive label. Itwas also noted that liver extraction recovery was 83%before pepsin digest and 6.9% additional recovery afterdigest. Kidney extraction was 97% before pepsin with anadditional 4.6% recovery from the digest. Omental, renaland subcutaneous fat yielded 35, 94 and 92% recovery,respectively, before pepsin digest with an additional 28%recovery from omental fat only by pepsin digestion.Protease digestion in these tissues yielded insignificantlevels of TRR recovery.

The Lowery/Dupont experiment with 5 laying hensstudied the metabolism of 14C-radiolabeled N-acetyl-glyphosate [35]. Birds were dosed by capsule twice perday for seven days with pure N-acetylglyphosate. Tworadiolabeled substances were found in the chickenexcreta and identified by HPLC, N-acetylglyphosate

82%) and glyphosate (0.8%). Residues of N-acetyl-glyphosate, AMPA, glyphosate and N-acetyl AMPAwere identified in the liver, as well as six distinctradiolabeled residues in the abdominal fat. Sequentialtreatment with pepsin and protease enzymes of the totalradioactive residues (TRR) remaining in the liver and eggyolk samples liberated additional radioactivity (4.1–14.7%TRR in toto), suggesting that glyphosate had beenincorporated into the proteins.

A total of eight radiolabeled substances were foundin actual muscle tissue, including: N-acetylglyphosate25% (0.009 mg/kg); AMPA 17% (0.005 mg/kg);glyphosate 7.2% (0.002 mg/kg); N-acetyl AMPA 1.9%(0.001 mg/kg); and four additional metabolitesrepresenting 9% (0.003 mg/kg).

The highest bioaccumulated total radioactive residuein whole eggs was 0.36 mg/kg, occurring at seven days.Unmetabolized N-acetylglyphosate and metabolites ofAMPA, glyphosate and N-acetyl AMPA were 0.16,0.002, 0.014 and 0.003 mg/kg, respectively.

Egg whites and yolks were also examinedindividually. The results are summarized in Table 3.

Table 3. Distribution of total radioactive residues (TRR) of glyphosate metabolites and reaction products found in chickeneggs and tissues by liquid scintillation counting (LSC).a

a From Dupont, 2007 [35].b Differences during processing reflect losses (1.5% TRR) incurred during concentration and/or sample clean-up for HPLC.c Losses (32% TRR) during the process were attributed to non-selective adsorption to particulate matter in the concentrated

extract.d Not detected.e Not applicable.f Up to 4 components with no one component accounting for greater than 9% TRR (0.003 mg/kg eq).g Up to 2 components with no one component accounting for greater than 0.7% TRR (< 0.001 mg/kg eq).h Low levels of radioactivity in the concentrated digest precluded further characterization.

Component Composite egg Composite egg Liver Composite Composite white (day 1–7) yolk (day 1–7) muscle fat % mg/kg eq % mg/kg eq % mg/kg eq % mg/kg eq % mg/kg eq TRR TRR TRR TRR TRR TRR (mg/kg eq) na 0.010 0.229 0.505 0.033 0.057initial extract 94 0.009 81 0.187 96 0.483 87 0.029 92 0.053concentrated extract 94 0.009 80b 0.183 64c 0.322 87 0.029 92 0.053 AMPA - d - 0.91 0.002 6.7 0.034 17 0.005 11 0.007 glyphosate 11 0.001 5.7 0.013 16 0.084 7.2 0.002 39 0.023 N-acetyl-AMPA 4.3


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Glyphosate, like the canonical amino acids, iscapable of chemical modification and metabolism in vivo[29]. The glyphosate amino acid analogues that arereaction products of these processes are shown in Fig. 2.Glyphosate can be acetylated, methylated, formylatedand nitrosylated. Enzymatic deacetylation also recyclesthe acetylated molecule back to glyphosate. All of thesemodifications will impact the potential for glyphosate to

be taken up by the cell and will change its reactionchemistry. For example, amino acid methylation generallymakes the molecule both more water-soluble and morefat-soluble, as well as lowering the activation energy[36]. Fig. 3 shows metabolites of glyphosate that werefound during Monsanto’s experiments on rats. N-acetylAMPA was identified by Dupont.

Figure 2. Glyphosate-derived amino acids identified by Monsanto exhibiting typical amino acid modifications.

Figure 3. Metabolites and manufacturing contaminants of glyphosate.


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3. DNA DAMAGE: CHROMATID DELETIONS ANDACHROMATIC LESIONS

One of Monsanto’s early studies involved examiningDNA damage in bone marrow of mice exposed toglyphosate [37]. An interesting finding was a substantialincrease in the number of chromatid deletions and achro-matic lesions observed following glyphosate exposurecompared to controls (Table 4). Achromatic lesions(gaps) in chromatids are induced by endonucleases thatplay a rôle in the repair process. These gaps are amanifestation of unrejoined DNA double-strand breaksfollowing endonuclease activity [38]. A possibleexplanation for the observed lesions involves impairedDNA repair mechanisms, particularly concerning thenucleotide guanine. 7,8-dihydro-8-oxoguanine (8-oxoG) isone of the most commonly formed oxidative lesions inDNA [39]. It is particularly destructive because it mispairswith adenine during replication, changing guanine:cytosineto thymine:adenine. Premutagenic lesions accumulate inmice that are defective in the gene coding the DNAglycosylase enzyme, OGG1, which excises 8-oxoguaninefrom DNA [40].

Clustered DNA damage means multiple lesions inclose proximity. In particular, it has been demonstratedexperimentally that a lesion adjacent to an 8-oxoG ismore resistant to the endonuclease-based repair process[41]. OGG1 has a conserved glycine at position G42 thatplays an essential rôle in distinguishing 8-oxoG fromguanine [42]. A hydrogen atom binds to the N7 atom ofguanine during the formation of 8-oxoG, and thishydrogen atom is H-bonded to the carbonyl of the strictlyconserved glycine residue in OGG1 to secureattachment. That is how it can recognize the oxidized

A. Chromatid deletions: observed frequenciesb

Sampling time Control Glyphosate (1g/kg) pc 12 h 0.0035 0.0087 0.26 24 h 0.0071 0.0142 0.26

B. Achromatic lesions: observed frequenciesb Sampling time Control Glyphosate pc 6 h 0.0083 0.020 0.08 12 h 0.0052 0.016 0.08

a Table reproduced from Monsanto’s 1983 report [37].b No. of aberrations minus number of cells scored.c Probability to be the same as the solvent control as determined

by Student’s t test.

Table 4. Statistical analysis of data on chromatid deletionsand achromatic lesions in rat bone marrow cells, performedonly on data where the observed frequency for glyphosatetreatment was higher than that of the solvent control.a

form of guanine and distinguish it from the healthy,unoxidized molecule. Substitution of alanine for G42disrupts the binding due to steric hindrance. With OGG1impaired through glyphosate substitution for glycine, onecan expect an accumulation of unrepaired 8-oxoG,leading to an increased frequency of clustered DNAdamage and double strand breaks, and therefore ofchromatid deletions and achromatic lesions, as observedby the Monsanto researchers. Mice with impaired OGG1function develop increased adiposity, fatty liver diseaseand impaired glucose tolerance [39]. A defective versionof this gene is linked to type-II diabetes in humans [43, 44].

4. METABOLIC AND SIGNALING DISORDERS

In this section we will examine several classes ofenzymes that contain conserved glycines with essentialrôles. We show that glyphosate substitution for glycine inhormone-sensitive lipase can explain an associationbetween glyphosate and obesity, as well as adrenalinsufficiency. The combination of protease inhibition andenhanced kinase activity can be predicted to causeexcessive phosphorylation systemically. Phosphorylationis a widespread modification with profound effects onaffected molecules, which can increase risk to bothAlzheimer’s disease and cancer. Pulmonary oedemainduced by glyphosate can be explained through proteinphosphatase inhibition.

The insulin receptor has conserved glycines that arenecessary for its transport from the endoplasmic reticulum(ER) to the plasma membrane. Insufficient insulinreceptor availability leads to hyperglycaemia anddiabetes. Cytochrome c oxidase (COX) is the enzymeresponsible for the final step of ATP synthesis in themitochondrion. Substitutions for conserved glycines inCOX severely impair oxidative phosphorylation. This canexplain glyphosate’s known toxicity to mitochondria.Kelch-like ECH-associated protein 1 (KEAP1) is aprotein that regulates nuclear factor erythroid 2-relatedfactor 2 (Nrf2)-like activity. It depends on a conservedglycine to prevent Nrf2 migration into the nucleus toactivate multiple genes. Nrf2 overactivity can directlyexplain the beak deformities observed in chickadees fedsunflower seeds that were sprayed with glyphosate justbefore harvest. Nrf2 overactivity is also linked to fatty liverdisease.

Hypothyroidism in the mother is a risk factor forautism in the child [45]. Disruption of conserved glycinesin the pituitary gland can lead to insufficient release ofthyroid-stimulating hormone. Conserved glycines alsoplay a rôle in adrenocorticotropic hormone (ACTH)release, and ACTH deficiency has been linked to adrenal


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insufficiency induced by glyphosate [46]. Both sulfatesynthesis by endothelial nitric oxide synthase (eNOS)and the removal of sulfate from bioactive sulfatedmolecules can be predicted to be impaired uponglyphosate for glycine substitution at critical locations oneNOS and arylsulfatases. eNOS also depends onconserved glycines for nitric oxide synthesis. Impairednitric oxide synthesis leads to hypertension.

4.1 Impaired cholesterol and fat metabolism

Lipases and esterases are an important group of enzymesthat hydrolyse ester bonds. They contain a characteristicgly-xaa-ser-xaa-gly (GXSXG) motif; the essential activeserine residue imparts the name “serine hydrolases” [47].The hydrogen bond donated by the first glycine of themotif plays a critical rôle in the catalysis [48–50]. Anespecially interesting subclass of serine hydrolases arethe hormone-sensitive lipases (HSLs) which, in humans,are responsible both for lipid hydrolysis and cholesterolester hydrolysis [51]. HSLs respond to adrenalin,catecholamines and ACTH by initiating the release offatty acids from adipose tissue as a source of fuel for thetissues [52]. HSLs are closely related to several bacterialproteins [53–55], and more distantly related toacetylcholinesterase and lipoprotein lipase. Hydrolasedisruption leads to lipotoxic effects that can promotemitochondrial dysfunction, induce endoplasmic reticulum(ER) stress, induce inflammation, and compromisemembrane function leading to apoptosis [56]. ImpairedHSL function has been linked to obesity, atherosclerosisand type 2 diabetes [51].

In addition to the conserved GXSXG motif, membersof the mammalian HSL class also contain the tetra-peptide histidyl-glycyl-glycyl-glycine (HGGG) motif in aconserved region described as an “oxyanion hole” [57,58]. This is a critical element in the catalytic machineryof diverse proteolytic enzymes (notably serine proteaseand certain caspases), which stabilizes negative chargebuild-up in the substrate via hydrogen bonds.

Monsanto’s chronic studies in mice and rats cited inour previous work [29] found considerable tissuedestruction by glyphosate in the pituitary, thyroid,thalamus, testes and adrenal glands, as well as majororgans. A 1990 study by Stout and Rueker revealedsignificant cortical adenomas, benign and metastaticpheochromocytomas and ganglioneuromas in male andfemale animals. A 1983 Knezevich and Hogan chronicstudy of glyphosate in mice revealed lymphoreticulartumours that “tended to be more frequent in treatedanimals, particularly the females.” It revealed cortical celladenoma and lymphoblastic lymphosarcoma of the adrenals.

A previous 1982 chronic study in rats by Lankas and

Hogan also showed neoplastic phenomena in theadrenals, including reticulum cell sarcoma, pheochro-mocytoma, cortical adenomas and malignant lymphomaof the adrenals particularly in the female animals.“Pheochromocytoma of the adrenals was the secondmost common tumour found among male animals. Mostfrequent neoplastic changes of glands was seen in thepituitary gland which was highest in females” [59].

HSLs play an essential rôle in the adrenal glands asa first step in adrenal hormone synthesis from cholesterol[60]. The glyphosate-containing herbicide Roundup hasbeen shown experimentally to severely impair adrenalhormone synthesis [46]. A glyphosate substitution forglycine in the GXSXG motif and/or the HGGG motifwould disrupt protein function. This would also explain alink between glyphosate and obesity, due to impairedrelease of stored fats. The correlation between Roundupuse on corn and soy crops and obesity in the USA asdetermined by data from the Centers for Disease Control(CDC) is very strong (R = 0.96, P = 2 × 10–8) [30].

4.2 Protease inhibition

Because excess expression of metalloproteinases isimplicated in metastatic cancer, there is considerableinterest in developing compounds that can inhibitprotease activity [61]. Much effort has gone intodeveloping protease inhibitors based on a phosphonylmoiety [9, 62]. The discovery of very potent irreversibleinhibitors based on phosphonyl fluoride led to their use inin vitro studies, but they are highly unsuitable fortherapeutic inhibition because they react withacetylcholinesterase, making them extremely toxic.Glyphosate, like phosphonyl fluoride compounds, has alsobeen shown to inhibit acetylcholinesterase [63].

As a consequence of the toxicity of phosphonylfluoride-based protease inhibitors, there has been a focusshift towards the concept of peptidyl phosphonate esters,because these can be hydrolysed, and because they canbe designed to be specific to a narrow class of proteases.The attached polypeptide chain can be tuned to match thespecificity of the target enzyme. Their mechanism ofaction is complex, but it involves a stable tetravalentphosphonylated derivative where one of the phosphonateoxygens is extended into an oxyanion hole (details can befound in [9] in the section beginning on p. 90). It can beexpected that glyphosate’s phosphonyl group might havea similar effect and, because of glyphosate insertion intoa large number of different peptide sequences, theconsequence of inhibition of multiple proteases byvarious glyphosate-containing short peptide chains, withunpredictable outcomes, can be expected.


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4.3 Protein kinases, cancer and Alzheimer’s disease

The human genome contains about 518 putative proteinkinase genes, which constitute about 2% of all humangenes [64]. Protein kinases contain a glycine-rich domainin the vicinity of the ATP-binding lysine residue in the N-terminal domain. The glycine-rich loop anchors thephosphate of ATP in a cleft just below the loop, and thenearby positively charged conserved lysine secures thenucleotide in place [65]. Protein kinase CK2 is a highlyversatile molecule, able to phosphorylate more than 160substrates on serine, threonine and tyrosine, using bothATP and GTP as phosphate donors [66]. It is involved insignal transduction and cell cycle regulation, cellproliferation and oncogenesis. A conserved regioncontains a glycine-rich loop (GXGXXG) that is also foundin other protein kinases [67]. A model has proposed thatthe GXGXXG residues form an elbow around thenucleotide [68]. The second glycine, G48, is conserved in99% of protein kinases, and it plays a fundamental rôle.Its replacement by negatively charged residues gives riseto mutants with improved kinetic properties for thepeptide substrates. Insertion of a negatively chargedresidue favours faster release of ADP from the ATPpocket, leading to increased activity. It can be expectedthat glyphosate substituting for any of the conservedglycines in protein kinases, but especially G48, willincrease protein activity.

Cyclin-dependent kinases (CDKs) are central tocontrol of eukaryotic cell division. Their activity isregulated through phosphorylation and dephosphorylationof conserved threonine and tyrsosine residues [69].GEGTYG is a highly conserved motif in CDK1, CDK2,CDK3, CDK5 and CDK10 [70]. This motif is referred toas the “G-loop,” and the adjacent glycines are essentialfor maintaining the flexibility to control activation/inactivation by phosphorylation of the interveningthreonine and tyrosine in the sequence GTYG. All theCDKs except CDK7 maintain the motif GXGXXG.

It has been suggested that overactivity of proteinkinase CK2 plays an important rôle in cancer [71]: CK2overexpression protects cellular proteins from caspaseaction and subsequent apoptosis. This leads to thetransformation to a tumorigenic form supporting survivaland proliferation. Imatinib (Gleevec) is a remarkablyeffective tyrosine kinase inhibitor used in chemotherapyto treat patients with leukaemia and breast cancer [72].Many other drugs based on suppression of proteinphosphorylation are under development [73].

Glycogen synthase kinase 3 (GSK3) is aconstitutively active, proline-directed serine/threoninekinase, also containing a highly conserved glycine-rich N-terminus [74]. Its overexpression has been linked to

Alzheimer’s disease [75]. Overexpression of GSK3 canresult in the hyperphosphorylation of tau, memoryimpairment, the increased production of β-amyloid (Aβ)and in the inflammatory response. GSK3 also reducesacetylcholine synthesis, and cholinergic deficit is afeature of Alzheimer’s disease [76]. GSK3 also mediatesapoptosis, which will promote the loss of neurons.

4.4 Insulin receptor activity and diabetes

The insulin receptor (IR) is a transmembrane tyrosinekinase receptor activated by both insulin and the insulin-like growth factors IGF-I and IGF-II. Defective IRactivity can lead to type 2 diabetes [77], which has reachedepidemic proportions throughout the industrialized world.The incidence of diabetes has been going up over time inthe USA exactly in step with the increased use ofglyphosate on core crops [30]. Knockout studies on mice,in which the insulin receptor of the α-cells of the pancreaswere impaired, demonstrated that glucagon release isregulated by these receptors and, when they are dysfunc-tional, the mice display hyperglucagonaemia, hypergly-caemia and glucose intolerance [78]. A significantincidence of pancreatic islet cell tumours were reportedin Monsanto studies in 1981 and 1990 (data shown in [29]).

A loosely conserved motif in two families of receptortyrosine kinases, insulin receptors and epidermal growthfactor receptors is characterized by a central glycineresidue that allows for a turn in the secondary structureof the protein [79]. This glycine residue has an upstreamα-helix and a downstream β-sheet. Receptors for insulinand epidermal growth factor both contain at least 8repeats of this motif. The glycine-centred motif in the IRis thus very important in determining its three-dimensional structure [80]. A patient with leprechaunism,a genetic syndrome associated with extreme insulinresistance, had two mutations in the gene for IR, one ofwhich was a glycine in this conserved loop [81]. Argininewas substituted for gly366 in the first repeat of the loop,and alanine displaced a conserved hydrophobic valineresidue. Both mutations impair post-translational processingand intracellular transport of the receptors to the plasmamembrane. Most likely, these two mutations inhibit thefolding of the proreceptor into its normal conformation[80]. This results in its retention within the ER, andtherefore post-translational processing steps in the Golgiapparatus are blocked. The result is a great reduction inthe number of receptors that are transported to the plasmamembrane and, therefore, impaired glucose uptake.


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4.5 Cytochrome c oxidase

Glyphosate has been shown to disrupt oxidativephosphorylation in mitochondria, although this effectrequired dosages that were much higher than would beexpected in realistic physiological situations [82].Glyphosate in combination with surfactants has beenshown to cause mitochondrial damage and induceapoptosis and necrosis [83]. It is possible that glyphosateinduces toxicity to mitochondria through an effect oncytochrome c oxidase (COX), and that the surfactantsenable glyphosate’s entry into the cell and the mitochondria,greatly increasing its toxic effects on the latter [84].

This would be especially so for the salts and estersof glyphosate, which are more soluble than glyphosatetechnical acid (N-phosphonomethylglycine), which wasused in Monsanto’s chronic animal studies. It is interestingto note that the active principles actually used in Roundupglyphosate-based herbicide formulations in real-worldapplications are not solely the technical acid but ratherthe far more soluble salts and esters of glyphosate; i.e.,potassium glyphosate, sodium glyphosate, ammoniumglyphosate and the popular isopropylamine glyphosate.These formulations have been shown to be orders ofmagnitude more toxic than glyphosate in isolation [85].

COX catalyses the one-electron oxidation of fourmolecules of reduced cytochrome c and the four-electronreduction of oxygen to water. It is an essentialcomponent of the oxidative phosphorylation pathway inmitochondria that produces adenosine triphosphate(ATP), the “energy currency” of cells. Subunit II of COXcontains a CuA redox centre, serves as a binding partnerfor cytochrome c, and as a participant in the electrontransfer process [86]. Subunit II has a highly conservedglycine residue at the active site [87–89]. A mutant formof COX in Rhodobacter sphaeroides involving asubstitution of valine for the conserved gly283 resulted ina complete block of access of oxygen to the active site[88]. Similarly, conversion of a conserved glycine in subunitII’s active site to arginine in a yeast strain resulted inrespiration deficiency [89]. A structural model of theredox center of subunit II includes two conservedglycines at positions 219 and 226, in close proximity toconserved amino acids that act as ligands to the CuAredox site and a glutamic acid residue implicated incytochrome c binding, as schematized in Fig. 4 [90].Obviously, substitution of glyphosate for glycine in eitherof these conserved sites would almost certainly harmenzyme function, leading to both impaired energygeneration and oxidative damage. Glyphosate is also astrong chelator of copper, having a higher metal chelateformation constant—11.93—compared to its affinity formanganese (5.47), zinc (8.74) and calcium (3.25).

4.6 Nrf2, KEAP1, fatty liver disease and birdbeak deformities

Nrf2 is a leucine zipper protein that protects againstoxidative damage due to an inflammatory responsefollowing various environmental triggers [91]. Interestingly,tumour cells often overexpress Nrf2, and this allowsthem to thrive in the face of severe oxidative stress [92–96]. High levels of Nrf2 activity cause chemotherapeuticresistance and correlate with a poor prognosis [94, 97].

Remarkably, although Nrf2 is cytoprotective,unregulated expression of Nrf2 is lethal in mice. Nrf2 isconstitutively expressed, and KEAP1 is a cytoplasmicprotein that regulates Nrf2 expression by binding to it toprevent its migration into the nucleus, thus enablingubiquitination and subsequent degradation [98, 99]. Miceengineered to be KEAP1 deficient died postnatally,probably from malnutrition due to hyperkeratosisobstructing the oesophagus and forestomach [100]. Theissue is that Nrf2 activates squamous epithelial cells tooverproduce keratin, and a thickened oesophaguseventually becomes completely blocked.

KEAP1 maintains a cytoplasmic anchor throughscaffolding with the cytoskeleton [98, 101]. The bindingprocess depends upon a conserved region of the proteincontaining a sequence of two glycine residues (doubleglycine repeat, DGR). KEAP1 acts as a sensor forelectrophilic and oxidative stresses to maintain anappropriate amount of Nrf2 activity. KEAP1 responds tooxidative stress through oxidation of sulfhydryl groups inconserved cysteine residues, and this causes it to releaseNrf2, permitting its survival and entry into the nucleus,where it activates many phase 2 antioxidant defences

Figure 4. Schematic of structure of subunit II of cytochrome coxidase (COX). Non-conserved amino acids are indicatedby *. Adapted from Holm et al. (1987) [90].


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[102]. Unregulated overactivation of Nrf2 due toimpaired KEAP1 function can be expected to lead tohyperkeratosis.

A newly emerging disease termed “avian keratindisorder” has become widespread among birds in certainregions of North America, particularly the interior ofAlaska [103, 104], around the Great Lakes [105, 106],and off the coast of California (where agricultural runoffis a suspected factor) [107]. High rates of crossed beaksand other malformations were first noted around theGreat Lakes in the mid-1970s [103, 105, 106], which iswhen glyphosate was first introduced into agriculturalpractice.

Chickadees are the most affected species, and theyare known to frequent bird feeders supplying sunflowerseeds, which according to the USDA are primarily grownin California, Colorado, the Dakotas, Kansas, Nebraska,Minnesota and Texas. Glyphosate is used in pre-planting,burndown, staging and preharvest dessication onsunflowers and specifically recommended to reduce croploss due to feeding by wild blackbirds [108]. Frequentsightings of blackbirds with deformed beaks were firstreported in 1979 [109].

A detailed study of potential toxic exposures toblack-capped chickadees in Alaska, which investigatedmultiple toxic metals, organochlorine pesticides,polychlorinated biphenyls (PCBs), polychlorinateddibenzodioxins and polychlorinated dibenzofurans(PCDFs), was unable to identify any obvious exposure–disease relationship and, furthermore, the authorsadmitted that there was no known link between any ofthese chemicals and hyperkeratosis [104]. Notably,glyphosate was not studied. Avian keratin disorder is notpresent at birth, but rather develops over time and is mostcommon among adult birds. Some physically examinedbirds revealed a systemic hyperkeratosis not limited to thebeak. The most plausible explanation is that glyphosatesubstitutes for glycine in KEAP1, causing constitutiveexpression of Nrf2 leading to hyperkeratosis.

Non-alcoholic fatty liver disease (NAFL) hasbecome an epidemic worldwide in recent years [110].From 10 to 20% of patients with NAFL eventuallydevelop non-alcoholic steatohepatitis (NASH), cirrhosis,end-stage liver disease, and hepatocellular carcinoma[111]. Mallory–Denk bodies (MDBs) are cytoplasmicinclusions associated with both alcoholic and non-alcoholic steatohepatitis [112]. These bodies are enrichedin keratin, which is overexpressed through enhancedNrf2 expression [111].

Non-melanoma skin cancer is the most commonform of cancer among Caucasians [113]. Lankas andHogan (1982) found sebaceous gland adenoma, and

basosquamous cell tumour of the skin as well asfibrosarcoma, fibromas, neurofibrosarcoma, osteogenicsarcoma and mixed malignant tumour of thesubcutaneous tissue associated with glyphosate residueingestion by male rats during a 26-month study [59, 29].Hyperkeratosis is a common feature of non-melanomaskin cancer [114]. Laryngeal keratosis is a risk factor forsubsequent carcinoma [115]. Hyperkeratosis wasobserved in 2% of oesophageal biopsies performed on1845 patients, and was linked to invasive squamouscarcinoma of the oral cavity/larynx [116].

4.7 Tyrosine phosphatase and systemic inflammation

Glycine is a component of multiple sequence motifs thatare consistent patterns within various groups of proteinphosphatases. One sequence that includes a GXGsubsequence is found in tyrosine phosphatases [117].Another unique sequence containing two glycines isfound in serine/threonine phosphatases [118]. Severalacid phosphatases contain the conserved sequence,RHG [119]. A long signature motif found in a family ofglucose-6-phosphatases, as well as several acidphosphatases and lipid phosphatases, contains aconserved glycine residue near the middle of theconserved sequence [120].

Protein tyrosine phosphatases are a class ofenzymes that remove phosphate groups fromphosphorylated tyrosine residues on proteins, and theygenerally have an anti-inflammatory rôle [121]. Tyrosinephosphatases play a very important rôle in the developingimmune system, influencing the process of maturation ofT-cells, as well as in the immune response in the adult[122]. Defective versions of a haematopoieticallyexpressed cytoplasmic tyrosine phosphatase have beenassociated with multiple autoimmune diseases, includingsystemic lupus erythematosus, rheumatoid arthritis andtype 1 diabetes [123–127]. T-cell protein tyrosinephosphatase (TCPTP), a negative regulator of JAK/STAT and multiple growth factor receptors, is highlyexpressed in haematopoietic tissues [128]. Defects inthis gene have been linked to type 1 diabetes, rheumatoidarthritis and Crohn’s disease through genome-wideassociation studies [124, 128, 129]. Substitution of prolineor alanine for the conserved gly127 residue resulted in a400-fold decrease in catalytic activity [130].

Studies on TCPTP-deficient mice have greatlyenhanced our knowledge of this important protein [131–133, 128, 134, 135]. Homozygous TCPTP-deficient micebecome ill and die by three to five weeks of age [131–133, 128]. They exhibit severe anaemia and infiltration ofmononuclear cells into multiple tissues, along with adramatic increase in expression of proinflammatory


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cytokines systemically, including TNF-α, IFN-γ and IL-12[133]. More specifically, inflammation of the synovialmembrane and severe subchondral bone resorption ofthe knee were observed, along with significantly greaternumbers of osteoclasts in the femur [123]. HeterozygousTCPTP-deficient mice respond with excess cytokineproduction and exaggerated gut inflammation to epithelialinsults, inducing colitis [136].

Severe glyphosate-surfactant poisoning is manifestedby gastroenteritis, respiratory disturbances, altered mentalstatus, treatment-resistant hypotension, renal failure andshock [137]. The fatality rate ranges from 3 to 30%, andis mostly due to either pulmonary toxicity or renal failure.A case study from India specifically highlights pulmonaryoedema following acute poisoning, along with aprecipitous drop in blood pressure [138], probably due toloss of serum fluids into the abdominal and pleural cavities.

A paper from 1990 by Martinez et al. compared theeffects of an oral dose of Roundup on rats to intratrachealinstallations [139]. The oral dose induced pulmonaryoedema 6 h later, along with bloodstained weeping fromthe nose, diarrhoea, distended gastrointestinal (GI) tract,and ascites, suggestive of hypovolemic shock. Theintratracheal instillations were much more toxic at muchlower dose levels. A dose of 0.1 mg/animal caused 80%mortality, and 0.2 mg/animal gave 100% mortality.Pathological examination found haemorrhaging andcongestion in the lungs.

Protein tyrosine phosphatase plays a crucial rôle inprotection from pulmonary oedema by maintaining barrierfunction following an inflammatory episode [140, 141]. Itis conceivable that, following an acute inflammatoryresponse to glyphosate poisoning, glyphosate is taken upby cells and incorporated into newly synthesized tyrosinephosphatase, disabling its effectiveness. However,glyphosate would likely inhibit these phosphatases even inthe absence of direct incorporation into the peptide chain.An investigation into 15 different synthetic compounds, allof which contained a phosphonyl group, demonstratedtheir effectiveness in inhibiting both tyrosine and serine–threonine phosphatases [142].

Chronic obstructive pulmonary disease (COPD) isthe fourth largest cause of death in the USA. It has beenlinked directly to overexuberant kinase-based signalingcascades [143]. Enhanced kinase activity combined withimpaired ability to turn off the signal through dephosphory-lation, both of which can be explained by glyphosateinterference, can easily account for such a pathology.

Monsanto’s sealed documents filed with the USEPA for the registration of glyphosate technical acidshow that glyphosate has adverse effects on the lungs ofanimals. We previously reported tumours found in the

lungs of test animals [29]. The study authors also notedmany non-neoplastic microscopic findings. In 1981,Lankas and Hogan reported that the more commonfindings were changes in the kidneys and lungs. The lungsof many of the rats had “changes associated with chronicrespiratory disease such as the presence of peribronchialand perivascular mononuclear cells and foci of macroph-ages in alveoli.” In addition, some of the physical symptomsincluded nasal discharge, excessive lacrimation and rales(abnormal crackling noises) caused by disease andcongestion of the lungs. Tumours of lungs were alsofound and included reticulum cell sarcoma, malignantlymphoma, adenocarcinoma and carcinomas.

Monsanto’s studies found that radiolabeled carbon inglyphosate was able to be recovered in the exhaledbreath of rats [29]. Pseudomonas aeruginosa is amongthe very few microbial species that are known to be ableto metabolize glyphosate and use it as a source ofphosphorus [144]. P. aeruginosa infection has been linkedto COPD [145]. Glyphosate is known to disrupt bacterialhomeostasis leading to an overgrowth of resistantpathogens; it was found by the USGS to be present in theatmosphere [146]; thus inhalation of the compound (notjust ingestion) would also harm the lung.

4.8 Hypothyroidism due to impaired thyroid-stimu-lating hormone activity

In [45], it was proposed that impaired activity ofmanganese-dependent protein phosphatase 1 (PP1)could explain a link between autism and maternalhypothyroidism, due to a dependency on PP1 for thepituitary to release thyroid-stimulating hormone (TSH).In that paper, it was argued that glyphosate chelation ofmanganese might severely decrease manganese bioavail-ability. This argument was supported by the extremelylow serum levels of manganese found in dairy cowsexposed to GM Roundup-Ready feed [147].

However, we have already seen that phosphatasescontain conserved glycine motifs that are essential fortheir proper functioning. Another distinct possibility is thatglyphosate substitutes for glycine directly in theconserved CAGYC region of the β-subunit of TSH itself.A rare mutation where the central glycine in CAGYC isreplaced by arginine in an autosomally recessive traitresults in cretinism (mental and growth retardation)[148]. This single mutation leads to the synthesis of adefective form of the β-subunit of TSH, which renders itunable to associate with an α-subunit. This results insevere systemic deficiency of TSH and hypothyroidism.It is plausible that a similar disruption of adrenalstimulation occurs because of glyphosate substitution fora conserved glycine in ACTH [149]. A homozygous


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substitution of glycine by valine in codon 116 of ACTHresulted in a profile of seizures, hypoglycaemia, impairedimmune function and respiratory distress, characterizedas “ACTH resistance syndrome.”

4.9 eNOS, sulfate and red blood cells

Endothelial nitric oxide synthase (eNOS), whichresembles cytochrome P450, plays a crucial rôle inproviding the signaling molecule, nitric oxide, in thevasculature [150]. NO induces smooth muscle cellrelaxation in the artery wall, leading to improved vascularflow. eNOS is dynamically regulated at thetranscriptional, post-transcriptional and post-translationallevels. Much has been written about eNOS’s“pathological” production of superoxide under certainconditions, especially when the cofactortetrahydrobiopterin (BH4) is depleted [151, 152].Regulatory control of eNOS is complex, and, in particular,it only produces NO when it is both phosphorylated anddetached from its secured scaffold to caveolin in lipidrafts in the plasma membrane [153]. Caveolin-1 preventscalmodulin binding under low calcium conditions [154,155] Excess calmodulin, produced in response to calciumsignaling, triggers the release of eNOS from its caveolin-bound site [156], and subsequent phosphorylation enablesNO production.

In [157, 158], it was proposed that eNOS is a“moonlighting enzyme” which, when membrane-bound,rather than being inactive, produces sulfate, catalysed bysunlight. The superoxide is drawn into a zinc-occupiedcavity created by the eNOS dimer, where it oxidizessulfane sulfur, bound to conserved cysteine residues [159,160] that encircle the cavity, to produce free sulfate.Details can be found in [157].

Red blood cells (RBCs) contain significant levels ofeNOS, which is permanently located just within theplasma membrane. This has presented a puzzle toresearchers, and some have even suggested that it isresidual, because NO would be rendered ineffectivethrough binding with haemoglobin, which would alsodisrupt oxygen transport [157, 161]. RBCs also steadilyproduce cholesterol sulfate, which plays an important rôlein maintaining their membrane negative charge andprotects them from lysis and aggregation [162, 163].Insufficient cholesterol sulfate leads to a high rate ofhaemolysis and shortened life span. Thus, RBCs plausiblyuse their eNOS to produce sulfate, which is thenconjugated with cholesterol and exported to the externalmembrane wall.

eNOS is a member of a class of NOS isoforms thatincludes inducible NOS (iNOS) and neuronal NOS(nNOS). All known members of this class contain a

conserved glycine residue (gly450), including all mam-malian NOSs as wall as avian and insect NOS enzymes[164]. Gly450 is essential for NOS dimerization.Conservative amino acid substitutions at gly450 ofmurine iNOS abolishes NO production, dimer formation,and BH4 binding to the enzyme [165]. Furthermore,eNOS uniquely (compared to iNOS and nNOS) containsa myristoyl group covalently attached to the conservedN-terminal glycine, gly2, which is essential for securingeNOS to the membrane [164, 166]. It has been proposedthat the myristoylating enzyme has an absolute specificityfor glycine [23]. Experiments in which the glycine wasreplaced by alanine showed that neither myristoylationnor palmitoylation took place, and thus the defectiveenzyme only appeared in the cytoplasm [167–170].

It should be noted that other enzymes also have aconserved N-terminal glycine that supports myristoyla-tion, including cyclic AMP-dependent protein kinase[171], calcineurin B [172], neurocalcin [173] andNADH–cytochrome b5 reductase [174]. Neurocalcin isfound mainly in retinal photoreceptors and in neurons,where it is involved in the transduction of calcium signals[175]. Neurocalcin binds to clathrin, tubulin and actin inthe cytoskeleton via myristoylation, and this suggests itmay play a rôle in moderating clathrin-coated vesicletraffic [176]. This rôle would be disrupted if glyphosatereplaces glycine at the N-terminus.

Thus, it becomes apparent that, if glyphosate issubstituted for glycine at either the gly2 or the gly450sites, eNOS will malfunction in both of its rôles ofproducing either sulfate or nitric oxide. This will havewidespread pathological effects related to excessivehaemolysis (anaemia), insufficient supply of cholesterolsulfate to the tissues, and insufficient production of NO,leading to vascular constriction and hypertension.Disruption of iNOS function will lead to impairedimmunity, since iNOS defends the host against infectiousagents [177]. And, of course, other important enzymesthat also support myristoylation via a terminal glycine willbehave in unpredictable ways when that glycine isreplaced with glyphosate.

4.10 Arylsulfatases

Arylsulfatases are a family of enzymes that removesulfate from sulfated molecules. Substrates include: thesulfated glycosaminoglycans—keratin sulfate, chondroitinsulfate and heparan sulfate; the sulfated sterols—cholesterol sulfate, estrone sulfate, testosterone sulfate,DHEA sulfate etc.; sulfated phenolic compounds; and thesulfated lipids such as sulfatide (sulfatedgalactocebroside). A defective version of arylsulfatase A,which removes sulfate-21 from sulfatide, results in the


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condition of metachromatic leukodystrophy [178]. Theinfantile form of this genetic disease is characterized bymuscle wasting and weakness, muscle rigidity,developmental delays, blindness, convulsions, impairedswallowing, paralysis and dementia. Life expectancy isbelow five years.

All members of the arylsulfatase family are subjectto a unique modification that is necessary for activation,involving the transformation of a cysteine residue intoformylglycine (FGly) [179]. In a rare inherited disordernamed multiple sulfatase deficiency (MSD), the activitiesof all sulfatases are severely reduced. This disorderinvolves an impairment in the transformation of cysteineto FGly. A highly conserved motif consisting of fouramino acids (LTGR) is found in all human and microbialarylsulfatases, near the modified cysteine. A 16-mersegment including this motif is essential and sufficient forthe formation of FGly [180]. It is likely that the conservedglycine residue in the motif is essential to support theflexibility needed to present the cysteine to the modifyingenzyme [181]. Without this transformation, the enzyme iscompletely inactive. Therefore, displacement of this glycineby glyphosate would likely disrupt enzyme activation.

In a mouse model of autism, maternal immuneactivation through polyinosinic:polycytidylic acid(poly(I:C)) injection produced offspring withcharacteristic features of mouse autism [182]. Likely duein part to a leaky gut, these offspring had sharplyelevated serum levels of 4-ethylphenylsulfate, producedby the gut microbes, with a 46-fold increase overcontrols. Injection of 4-ethylphenylsulfate into normalmice induced autistic behaviour. It is plausible thatimpaired phenol sulfatase activity, particularly in thecontext of a leaky gut, would cause the accumulation ofsulfated phenols in the plasma, contributing to autism.

5. NEURODEGENERATIVE DISEASES

We have already seen that the pathology of Alzheimer’sdisease is linked to overexpression of GSK3, which canbe induced by the substitution of negatively chargedamino acids in place of glycine in the N-terminal region.Glyphosate is negatively charged at biological pH.

Beyond Alzheimer’s, multiple neurodegenerativediseases are associated with aggregated and tangledproteins including Lewy bodies, tauopathies, senileplaques and neurofibrillary tangles. In this section, we willfocus on four classes of neurodegeneration that can belinked to disruption of conserved glycines in specificmisfolded proteins: prion diseases, Alzheimer’s disease,Parkinson’s disease and amyotrophic lateral sclerosis(ALS). In all four of these cases, it has been determinedthat rare soluble non-fibrillar forms of the aggregated

proteins are much more damaging than the insolubleprecipitates. It has also been shown that conservedglycines support the flexibility that is needed to allow thehydrophobic components of the molecule to assemble soas to precipitate out of aqueous solution. Glycine ishydrophobic, whereas glyphosate is amphiphilic, and it isalso much bulkier than glycine. Glyphosate’s solubilitywould likely be higher in the cytoplasm of a cell than inserum both because of the higher pH and because ofcationic buffering by potassium. In fact, potassium saltsare used in glyphosate formulations to increase itssolubility. It seems plausible that the rare soluble non-fibrillar forms of aggregated proteins that are toxic haveglyphosate in place of glycine in their structure.

5.1 Prion diseases

Prion diseases, also called transmissible spongiformencephalopathies, are novel degenerative diseases inwhich the infective agent is a misfolded protein. Prionsare believed to be responsible for Kuru, Creutzfeldt-Jakob disease, and bovine spongiform encephalopathy(BSE, mad cow disease). BSE first appeared in theUnited Kingdom in 1986, after glyphosate had been usedto control weeds in animal feed for at least a decade.While BSE is believed to be caused by feed contaminatedwith the brain, spinal cord or digestive tract of infectedcarcasses, there remains the open question of whatcaused the original appearance of misfolded proteins toinitiate the infection. Prion proteins contain a glycine-richhydrophobic region that shows almost perfect conserva-tion across a wide range of species. This region appearsto be important for the misfolding process and prionpropagation [183]. It seems remarkable that a highlyconserved region of the protein, unaltered by geneticmutations, could be the source of the toxicity. The normalform of prion proteins, PrPC, is rapidly catabolized,whereas a pathogenic isoform, PrPSc, is highly resistantto proteolysis [184]. A subsequence containing only PrP106–126 is a highly conserved unstructured region ofPrP, which is considered to be the main contributor tofibrillogenicity. It has a high tendency to aggregate into aβ-sheet structure forming amyloid fibrils in vitro [185, 186].

There is controversy regarding whether the toxicityis due mainly to mature fibrils or to protofibrillaraggregates. A definitive study [187] showed that twostrictly conserved glycine residues, at positions 114 and119, within the highly conserved region, are the maindrivers behind fibril formation, likely due to the highflexibility that they introduce in the molecular structure. Ifeither of these is substituted by glyphosate, fibrilformation would be impaired, due to the decreasedflexibility. Remarkably, although replacement of these


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glycines with alanine interfered with aggregate formation,it produced a higher concentration of a soluble non-fibrillar form which was, however, extremely neurotoxic[184]. Alanine has an additional methyl group, whichmakes it a bulkier molecule than glycine, restrictingflexibility of the assembled protein. Glyphosatesubstitution for glycine would be expected to be evenmore disruptive than alanine, given its additionalmethylphosphonyl group. The lack of flexibility toorganize the hydrophobic unit into a fibril will favour thetoxic soluble form of the peptide. Furthermore, glyphosatecan be expected to resist enzymatic degradation, andglyphosate-containing peptoids would also be resistant toproteolysis, in both cases due mainly to the highly stableC–P bond [188].

5.2 Alzheimer’s disease, prions and βββββ-amyloid

Alzheimer’s disease is the most common form ofdementia, accounting for 60% to 80% of all cases [189].Worldwide, the prevalence of dementia was more than35 million in 2010, and projected to be more than 65 millionby 2030 and 115 million by 2050 [190]. The incidence ofAlzheimer’s disease is increasing at an alarming rate inthe United States, in step with the dramatic rise in the useof glyphosate on corn, soy and wheat crops [30]. β-amyloid(Aβ) is now well established as a causal factor in Alzheimer’sdisease, although the mechanism of toxicity remainscontroversial [191]. The Aβ that accumulates in theAlzheimer’s brain consists of deposited insoluble fibrillarcomponents, monomers, and soluble oligomers, the latterbeing the most toxic form. The levels of the monomer andthe deposited precipitates are orders of magnitudegreater than the levels of the toxic soluble oligomers,which are known to cause both acute synaptotoxicity andneurodegeneration [190]. The pharmaceutical industryhas developed immunotherapies that target Aβ, but noneof them are specific to the toxic soluble form, and thislikely explains their lack of efficacy [192]. The challengeto the industry is to develop a drug that uniquely targetsthe soluble oligomers.

Growing evidence supports the concept that solublenon-fibrillar forms of Aβ are the most toxic, and theirtoxicity can be mimicked by a synthetic peptide containingthe first 42 residues (Aβ42) [193]. Interestingly, Aβ has aGXXXG domain with conserved glycines at positionsG29 and G33 [194]. Substitution of alanine in place ofglycine at residues G29 and/or G33 led to an attenuationof dimerization, and specifically increased the formationof Aβ38 and shorter species at the expense of Aβ42.Munter et al. argued that the glycines promotedimerization and that this impedes access of proteases tothe molecule, resulting in the survival of the longer peptide

chain. However, it is extremely unlikely that a highlyconserved element in the protein could be responsible fordisease. An alternative thought is that glyphosate substitutesfor glycine, increasing solubility and preventingproteolysis. This is in line with work that has shown thataminopeptidases can be disrupted by methylphosphonicacid [10]. It can be envisioned that the presence ofglyphosate in place of glycine upstream interferes withthe stripping off of residues 41 and 42 by γ-secretase,leaving behind a soluble and damaging Aβ42 peptide.

Magnesium deficiency has been linked to Alzheimer’sdisease [195, 196], and in vitro studies have shown thatlow magnesium leads to increased production of Aβ[197]. Glyphosate’s chelation of +2 cations can beexpected to deplete magnesium availability, and studies onsoy have shown that glyphosate interferes with magnesiumuptake in plants [198, 199]. The effect of low magnesiumwill work synergistically with glyphosate’s inclusion in theAβ peptide to induce Alzheimer’s disease (AD).

Bush, Cherny and others note that zinc, copper andiron accumulate in brain plaques [200–204]. Aβ is a Znand Cu metalloprotein, and zinc has been shown to induceamyloid formation in Aβ [200]. Glyphosate stronglychelates Cu, as well as Zn, and ferrous iron, Fe2+, which,as Monsanto’s John E. Franz notes, quickly oxidizes tothe ferric form, Fe3+. Metal chelate formation constantsshow strong binding potential for these elements at 11.9,18.2 and 6.9 for Cu, Zn and Fe respectively, as comparedto the parent amino acid glycine at 8.6, 5.4 and 4.3respectively. Maynard et al. (2005) assert: “Aβ and APP(amyloid precursor protein) expression have both beenshown to decrease brain copper (Cu) levels, whereasincreasing brain Cu availability results in decreased levelsof Aβ and amyloid plaque formation in transgenic mice.... Interestingly, the highest levels of free or synaptic Znare found in cortex and hippocampus, the regions mostaffected in AD. Zn2+ reuptake after synaptic release is arapid, energy-dependent process. Hence, energydepletion could cause a pooling of extracellular Zn2+,contributing to Aβ deposition” [203]. Glyphosate’sdisruption of COX could impair energy supplies, leading toexcess Zn2+ accumulation. Religa et al. show that zinclevels rise with tissue amyloid levels and “weresignificantly elevated in the most severely dementedcases (CDR 4 to 5) and in cases that had an amyloidburden greater than 8 plaques/mm2. Levels of othermetals did not differ between groups.” They concludedthat the zinc accumulation is dominant in cases ofadvanced Alzheimer’s disease and linked to brainamyloid peptide accumulation as well as to the severity ofthe disease [204]. Such a pairing of these elements withthe amino acid glyphosate in amyloid protein would likely


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form misfolded proteins as well as insoluble plaques dueto the known resistance of the analogue to proteolysis.

Because of its small ionic radius and strong positivecharges, aluminum firmly binds to metal-binding andphosphorylated amino acids, acting as a cross-linker bybinding multiple amino acids simultaneously [205], whichcan cause the oligomerization of proteins, inhibiting theirdegradation by proteases. This is believed to be amechanism for the neurofibrillary pathology ofphosphorylated tau protein [206, 207]. We have alreadyestablished that glyphosate likely induces excess proteinphosphorylation due to its excitatory effects on kinasesand inhibitory effect on phosphatases. However,glyphosate itself also binds aluminum, particularly througholigomeric complexation of an aluminum ion [208]. Thus,two molecules of a peptoid/peptide, both of which containglyphosate, will likely become linked together via analuminum ligand binding two embedded glyphosateresidues, one in each peptide. This would almost surelylead to impaired protein degradation and accumulation offibrils. In vitro studies have shown that soluble dimericand oligomeric forms of Aβ are more toxic thanmonomeric Aβ [209, 210].

Increasingly, prions are suspected of playing a rôle inAlzheimer’s disease. A recent, well-designed study hasdemonstrated that a triad formed from amyloid-β, PrPCand a metabolic glutamate receptor is critical for thedisruption of synaptic plasticity by the soluble non-fibrillarforms of Aβ [211]. High affinity binding of Aβ to PrP hasbeen localized to the region of PrP from residue 91 toresidue 119 [212]; within this region, residues 114 and 119are the two conserved glycines in PrP [184].

5.3 Cataracts and Alzheimer’s disease

Crystallin is the dominant protein found in the lens of theeye. Cataract formation is the result of amyloid proteinaggregation from crystallins, which results in insoluble β-amyloid deposits in the lens [213]. Post-mortem studieson Alzheimer’s patients revealed that Aβ is also presentin the cytosol of cells from the lenses of people withAlzheimer’s disease and that it is associated withcataracts [214]. In fact, amyloid plaques in cataracts andin the brain in Alzheimer’s patients were identical.Furthermore, α-B-crystallin is found in association withbrain plaques and fibrillary tangles in Alzheimer’s,Creutzfeldt-Jakob and Parkinson’s diseases.

An increase in phosphorylation of crystallin is linkedto increased cataract risk [215]. Such an increase can beexpected in the context of hyperactive kinases andinhibited phosphatases, such as is expected withglyphosate insertion in place of glycine in thesemolecules. Furthermore, a single mutation of the

conserved glycine-98 residue of crystallin to arginineresults in a defective form of the protein that lackschaperone function, and is susceptible to heat-inducedaggregation [216]. This mutation is also linked toincreased risk of cataracts. The α-crystallins in particularplay an important rôle in chaperoning crystallins toprevent protein aggregation and precipitation. Thus, itappears that alterations to glycine residues can play a rôlein cataracts that is completely analogous to the rôle theyplay in Alzheimer’s disease, and the two conditions areclosely linked.

Perhaps unsurprisingly, given these cataract riskfactors linked to defective crystallin, Monsanto’s ownearly rodent studies found a link between glyphosateexposure and cataract formation [29]. Monsanto’s 1990(Stout & Ruecker) chronic rat exposure study foundsignificant incidence of y-sutures and other ophthalmicdegenerative lens changes caused by glyphosate. Thepathologist for the study, Dr Lionel Rubin, noted in hisophthalmoscopic examination report that: “There appearsto be a dose-related occurrence of cataract affectingmale group M3. The type of cataract affecting this groupis the diffuse posterior sub-capsular type and to a lesserextent, anterior polar and sutural types.” Displacement ofpupils and ocular opacities in the presence of glyphosatewas also noted in 1983 by Knezevich and Hogan [29].

5.4 ααααα-Synuclein and Parkinson’s disease

A 35-amino-acid peptide was isolated from the insolublecore of Alzheimer’s disease amyloid plaque, and wasfound to be a fragment of α-synuclein, a neuronal proteinof unknown function. This fragment had a strikingsequence similarity with the carboxyl terminal of Aβ, aswell as a region of PrP implicated in amyloid formation[217]. α-synuclein aggregates are found in associationwith Lewy bodies present in Parkinson’s diseasepatients, and is also linked to dementia and multiplesystem atrophy [218, 219]. A novel ELISA test has beendeveloped that detects only oligomeric soluble aggregatesof α-synuclein in the blood. It was shown that 52% ofParkinson’s disease patients tested positive as againstonly 15% of controls [220]. A 9-residue sequence,66VGGAVVTGV74, containing three glycine residues, hasbeen shown to be crucial for the fibrillization and cytotoxicityof α-synuclein [221]. Fibrillization and cell toxicity arecompletely eliminated when this sequence is deleted.

5.5 TDP-43 and ALS

Transactive response DNA binding protein 43 (TDP-43)is a transcriptional repressor that binds both DNA andRNA, and has multiple other functions, including pre-


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mRNA splicing and translational regulation. Exon 6 ofTDP-43 encodes a C-terminal glycine-rich domainwhere multiple missense mutations have been implicatedin association with amyotrophic lateral sclerosis (ALS)and frontotemporal lobar degeneration (FTLD), asubtype of dementia [222]. TDP-43 is now considered tobe the signature class of inclusional lesions for sporadicALS. TDP-43 is also recognized for its ability to repressHIV transcription [223].

The C-terminus of TDP-43 bears sequencesimilarity to prion proteins. Synthetic peptides nearresidue 315 form amyloid fibrils in vitro and causecultured neuronal death [224]. Accumulation of protease-resistant fragments may spread the disease phenotypeamong neighbouring neurons, similar to the pathologyassociated with prion diseases.

TDP-43 is a member of a class of ribonucleoproteinsknown as 2XRBD-Gly proteins. The class share thecommon feature of a glycine-rich C-terminus thatprobably serves a similar function in all the members ofthe class. Among 53 unrelated sporadic or familiar ALScases, two of whom suffered from concurrent FTLD,29 different missense mutations in TDP-43 have beenreported [222]. All but one of them occurred in the C-terminal glycine-rich domain of exon 6. The subset ofthese mutations that involve a substitution for glycine areconcentrated in the region between residue 275 and 310,the most glycine-dense region of the C-terminus. Thus,replacing glycine with any other amino acid increases riskto ALS. Non-genetic replacement with glyphosate can beexpected to have a similar outcome.

About 20% of patients with familial ALS havemutations in Cu,Zn superoxide dismutase (SOD). One ofthe more common mutations found is a substitution ofalanine in place of glycine at gly93, which introduces amodest gain of function [225]. Although this changeappears to have little effect on enzyme activity,transgenic mice with this genetic mutation becomeparalysed in one or more limbs as a result of motorneuron loss in the spinal cord and do not live beyond fiveor six months. Clearly, substitution of a bulkier moleculein place of glycine disrupts the function of the enzyme inways that are not yet understood.

6. MICROBIOME DISRUPTION AND IMMUNE SYSTEMIMPAIRMENT

In this section we discuss several examples of proteinsthat play a rôle either in maintaining the health of the gutmicrobiome or in human defence against microbialinfection. In each case, conserved glycines are essentialfor protein function. We begin with a section on thedisruption by glyphosate of PEP carboxylase, which has

major impact on microbial health, as this enzyme iscentral to both carbon fixation and nitrogen fixation. Thenext section describes glycine riboswitches and their rôlein the metabolization of glycine in the medium via theglycine cleavage system. This is important both to detoxifyglycine and to supply methyl groups for one-carbonmetabolism. Antimicrobial peptides such as α-defensinare important for human immune function, and theseproteins contain conserved glycines. Finally, HIV-AIDSinfection is linked to impaired phosphatase activity,particularly a constitutively expressed tyrosine phos-phatase that is highly expressed in T-cells.

6.1 Nitrogen fixation and PEP carboxylase

Mung beans exposed to glyphosate at levels appropriatefor weed control show reduced fixation of nitrogen intoorganic matter [226]. Nitrogenase, an essential enzymein plants for nitrogen fixation, converts nitrogen gas toammonia, which is then conjugated with glutamate toproduce glutamine. A study on lupins showed thatglyphosate exposure, even at sublethal levels, severelyinhibited nitrogenase activity, resulting in a decrease instarch content and an increase in sucrose content. Thepractice of using glyphosate as a pre-harvest ripener insugar cane to increase yield exploits this property ofincreased sucrose production [227]. The mechanism wastraced to inhibition of phosphoenol pyruvate carboxylase(PEPC), subsequent to accumulation of shikimate viablockage of the shikimate pathway [228]. PEPC plays anessential rôle in the incorporation of both CO2 andnitrogen into plants [229, 230].

PEPC’s regulation is controlled by levels ofshikimate rather than through product inhibition. SincePEP is the input to both PEPC and 5-enolpyru-vylshikimic-3-phosphate synthase (EPSPS), the step inthe shikimate pathway that glyphosate disrupts, PEPaccumulates at ever greater levels while both thecarboxylase pathway and the shikimate pathway areblocked. Most of the carbohydrate pool is then exhaustedthrough conversion to shikimate, acting as a metabolicsink. Shikimate accumulates to very high levels due toglyphosate’s inhibition of EPSPS, while the synthesis ofaromatic amino acids, normally derived from shikimate, isblocked.

At the extreme C-terminus of PEPC there is aninvariant glycine residue which plays an essential rôle inenzyme activity [231]. Even the conservative replacementwith alanine (one extra methyl group) leads to loss offunction both in vivo and in vitro, with an experimentallydemonstrated drop to only 23% of the wild type activitylevel in sorghum [231]. In experiments on E. coli,perturbation of the terminal gly-961 by either


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conservative neutral substitution with alanine or valine oreven by specific deletion did not seem to cause anyapparent harmful effects. However, replacement with anegatively charged amino acid such as aspartate resultedin a complete shutdown of enzyme activity. The authorswrote: “PEPC appears to not tolerate additional negativecharge at its extreme C-terminus beyond that of the mainchain free CO2

– group.”Glyphosate substitution would of course represent

the introduction of additional negative charge. Thus, itseems almost certain that glyphosate substitution forglycine at this conserved terminal site would severelyinhibit the enzyme’s activity, beyond any inhibitionalready induced by the build-up of shikimate. This offersa further explanation for the empirically observedsuppression of PEPC by glyphosate, and it also suggeststhat glyphosate disrupts nitrogen fixation [232].

6.2 Glycine riboswitches

Glycine is both essential and toxic to bacteria. It is wellknown that glycine inhibits bacterial growth [233–236],by substituting for alanine into peptidoglycan precursors[237–239]. Glycine-containing precursors are poorsubstrates for peptidoglycan biosynthesis enzymes aswell as for the transpeptidation reaction, leading to both adeficiency in muropeptides and a high percentage ofmuropeptides that are not cross-linked. Thesemodifications to the cell wall severely restrict growth.

As a consequence of glycine’s toxicity, it is importantfor bacteria to be able to quickly break glycine down intobasic building blocks. Oxidative cleavage to CO2,

+4NH

and a methyl group is carried out by the glycine cleavagesystem (GCS), and the methyl group becomes a majorsource for one-carbon metabolism, beginning with theconversion of tetrahydrofolate (THF) to methylene-THF[237], which is then used to biosynthesize various cellularcompounds, including, importantly, purines andmethionine. The GCS also produces NADH in theoxidative cleavage step, which yields energy through theelectron transport system. As well the GCS is the mostprominent pathway for serine and glycine catabolism inhumans [240]. Mutations in GCS-encoding genes arelinked to defects in neural tube development, causingspina bifida and anencephaly [241, 242, 243].

Riboswitches are small non-coding RNA segmentstypically located in the 5' untranslated regions (UTRs) ofbacterial mRNAs, and they serve as both sensors ofcellular metabolites and effectors of regulatoryresponses. Studies have revealed the presence of glycineriboswitches in the 5' UTRs of the enzymes involved inthe GCS [244]. These riboswitches bind directly toglycine and turn on the genes for transcription of

enzymes needed to metabolize it. In this way, glycine isquickly cleared and put to good use, fueling the electrontransport chain and the one-carbon metabolismpathways. Glycine is highly toxic to mutants missingthese riboswitch regions; a medium containing only 1%glycine severely restricts their growth [237].

Glyphosate is a patented antimicrobial agent, and itstoxicity to humans has been attributed in part to its adverseeffect on the microbiome [26]. In addition to other actionssuch as metal chelation and inhibition of the shikimatepathway, glyphosate, acting as a glycine analogue, disruptsthe glycine regulatory system and cell wall construction.Glyphosate perhaps, like glycine, substitutes for alanine inthe peptidoglycans. Glyphosate likely also binds to theglycine riboswitches, acting as a glycine analogue, and itcould interfere with the signaling mechanism due to itsaltered structure and negative charge.

6.3 ααααα-Defensin and antimicrobial peptides

Human α-defensins are important members of a broadclass of antimicrobial peptides that are found throughoutthe tree of life [245, 246]. All of the human α-defensins,although their molecular structures are quite variable,contain a conserved glycine, gly17, which is part of aβ-bulge structure. Gly17 is in fact the only non-cysteineresidue that is invariant in α-defensins. Gly17 is part of alarger structural motif known as the γ-core, which ispresent across many classes of antimicrobial peptides.When other amino acids are substituted for gly17,dimerization is impaired, and this disrupts the ability toself-associate, inhibit anthrax lethal factor, and killbacteria [247].

Even the conservative substitution of L-alanine forglycine inhibits protein function. Bulkier hydrophobic sidechains are likely to create steric clashes, a polar side chainmight introduce hydrogen bonds, and a charged side chainmight invite electrostatic attraction or repulsion [247].Thus the methylphosphonyl group in glyphosate in placeof the conserved glycine is likely to have a major negativeimpact on the protein’s effectiveness against microbes.

6.4 HIV-AIDS

Protein tyrosine kinases (PTKs), acting in concert withprotein tyrosine phosphatases (PTPases), control levelsof cellular protein tyrosine phosphorylation. Changes intyrosine kinase and phosphatase activity are implicated innumerous human diseases, including cancer, diabetes andpathogen infectivity [248].

Impaired phosphatase activity due to disruption of aconserved glycine may play a rôle in increasing HIVinfectivity. c-Jun N-terminal kinases (JNKs) are signaling


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kinases that respond to mitogen-activated protein (MAP)kinase signaling and regulate many cellular activities.JNKs are activated through dual phosphorylation ofthreonine and tyrosine residues, and inactivated bymatched phosphatases [249]. JNK activation isimplicated in HIV infections. Quiescent (resting) humanperipheral blood T lymphocytes do not support efficientHIV infection, both because reverse transcription takeslonger and because of impaired integration of the viralcomplementary DNA [250]. Cellular JNK is only expressedfollowing activation, and it regulates permissiveness toHIV-1 infection. In JNK-activated T lymphocytes, viralintegrase is phosphorylated by JNK on a highly conservedserine residue in its core domain. This modification isrequired for efficient HIV-1 integration and infection. As

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