What factors influence protein function? What is denaturation ? What is inactivation?
What forces underlie the folding process? What are the consequences of protein misfolding?
Factors influencing protein activity Denaturation Vs inactivation
Denaturation ……Random coil: no specific shape.
Is it reversible?
Inactivation/activation form of regulation may be reversible or irreversible.
In/activation Covalent modification
Reversible: phosphorylation/dephosphorylation
Irreversible: Proteolysis
Acylation ex: Myristoylation, palmitoylation
Allosteric modulators positive and negative
Conformational: monomer - polymer
Denaturing Agents
Harsh mechanical treatment/handling
Heat
How does changes in temperature affect protein function?
Heat Kinetic energy
(Taq-polymerase), freezing and thawing
Acid-base: Charge disruption
Alcohol
Denaturating agents Salt concentration +NH4 > k> + Na + > Li + > Mg++ > Ca++ precipitating
Urea solubilizing Guanidium
Disulfide reduction Mercaptoethanol, Dithiothreitol…
Detergents:
SDS:
Sodium dodecyl sulfate, Sodium lauryl sulfate
Other denaturing agents Heavy metals: Pb, Hg, Cd, Ag
UV ionizing radiation
Will a denatured protein re-nature into its native conformation?
Anfinsen Experiment
Protein folding IS IT RANDOM?
What forces direct the folding?
∆ G = ∆ H - T ∆ S
Folding Pathways
Not random.
The folding process is rapid
Determined by the primary sequence and surrounding environment,
Requires sometimes accessory proteins.
Accessory Proteins
Prolyl cis –trans isomerase
Protein Disulfide Isomerase…… PDI
Chaperons
Prolyl cis-trans isomerase
Protein disulfide Isomerase (PDI)
Chaperons Heat shock proteins
HSP 70 ……. Blocks aggregation
HSP60 …… Provides isolation chamber
Protein Fate
Protein Misfolding
Protein Conformational Diseases
in 2ry and/or 3ry structure of functional protein
Loss of function or gain of toxic activity
PFD
PrPC/PrPSc
1. PrPSc bind to PrPC
2. Leads to “Flipping”
of PrPC into a beta-
sheet conformation
(PrPSc)
3. PrPSc can Polymerize
4. Lead to the formation
of fibrils and plaques
5. Deposit in brain
Sickle hemoglobin