Proteins

AMRUTHA K SCBPST

Protein is required in the body for growth and repair. Too much protein is used by the body for energy or stored

as fat.

Proteins

Over view

æ COLLAGENæ ADHESIVESæ ACTIN æ Dystrophin

INTRODUCTION

A protein is a complex, high molecular weight organic compound that consists of amino acids joined by peptide bonds.

They are large biological molecules, or macromolecules, consisting of one or more long chains of amino acid residues

A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors

Once formed proteins only exist for a certain period of time and are then degraded and recycled by the cell's machinery through the process of protein turnover.

PROTEINS IN THE BODY

During digestion proteins are broken up into amino acids. These are absorbed into the blood stream and made into new proteins in the body.

Twenty different amino acids are found in plant and animal sources.

Thousands of amino acids may be joined together to make one type of protein. The body can make eleven amino acids. The remaining nine have to be obtained from protein in the diet. These are known as essential amino acids.

BUILDING BLOCKS OF PROTEIN

PROTEINS FROM ANIMAL SOURCES

Proteins from animal sources (meat, poultry, milk, and fish) have a high quality because they contain all the essential amino acids in proportions similar to those required for synthesis of human tissue proteins

Gelatin prepared from animal collagen is an exception; it has a low biologic value as a result of deficiencies in several essential amino acids.

SOURCES OF PROTEIN HBV

Essential amino acids are found in animal protein, soya beans and Quinoa.

These are called High Biological Value proteins.

Sources of high biological value protein are

o Milk and milk based productso Eggs o Meato fisho Shellfisho Soya beanso Quinoa

SOURCES OF PROTEIN LBV

Proteins that come from plant sources other

than soya beans and Quinoa are Low

biological value proteins. This is because

they lack one or more of the essential amino

acids.

If these proteins are combined in the diet

like beans on toast your body can receive all

the essential amino acids.

Sources of low biological value protein

Quorn

Nuts/peanuts

Pulses

Rice

cereals

Animal-derived proteins are easily digested

and generally contain a mix of amino acids

that is very similar to ours (complete protein

source).   Plant sources of protein are not as

easily digested and more than one source of

plant protein is required in order to create an

optimum amino acid profile or complete

protein.   

COLLAGEN

Collagen is the main component of connective tissue.

Collagen is the major insoluble fibrous protein in the

body.

These are basic structural elements.

These proteins have special mechanical properties.

It is the most abundant protein in the body.

They are found as components of skin, connective

tissue, blood vessels, sclera and cornea of eye.

It is long, rigid structure in which three polypeptides

are wound around one another in a rope like fashion.

Polypeptide chains are held together by hydrogen

bonds.

These polypeptides are called α-helix

They are arranged in a triple helix.

They are found everywhere in the body, but their

type is dictated by their structural role in a particular

organ.

There are at least 16 types of collagen, but 80 – 90

percent of the collagen in the body consists of types

I, II, and III

Example:1. Gel- extracellular matrix or vitreous

humor of eye.2. Stacked- as in Cornea

2. Tight bundles- Tendons

3. Fibers arranged at an angle- Bones

Variations in the amino acids sequence of the α-chain result in the different properties of the chains

These α-chains are combined to form various types of collagen found in the tissues.

Type I - 2 α1& 1α2

Types of Collagen

FIBRIL-FORMING

Collagen type I Found in the supporting elements of

high tensile strength.

Found in skin, tendon, muscles, cornea and walls of blood vessels. scar tissue, the end product when tissue heals by repair, the endomysium of myofibrils, the organic part of bone, the dermis, the dentin and organ capsules.

₪ Found in cartilaginous tissues ,inter verteberal disk, vitreous body and hyaline cartilage.

₪ Type II collagen is the basis for articular cartilage and hyaline cartilage.

₪ It makes up 50% of all protein in cartilage and 85-90% of collagen of articular cartilage.

₪ It does form fibrils. This fibrillar network of collagen allows cartilage to entrap the proteoglycan aggregate as well as provide tensile strength to the tissue

Collagen type II

Collagen type III ◊ Found in distensible tissues.

◊ fetal skin, blood vessels.

NETWORK- FORMING

Collagen type IV

Found in the basement membranes and muscles.

collagen IV (ColIV or Col4) is a type of collagen found

primarily in the basal lamina.

Collagen type VII Beneath stratified squamous epithelia

Type VII collagen is a major component of the anchoring fibrils

of the dermal-epidermal adhesion on the dermal side at the

lamina densa/papillary dermis interface

FIBRIL- ASSOCIATED

Collagen type IX Found in cartilage

Collagen type XII Tendon, ligaments

STRUCTURE OF COLLAGEN

Amino Acid Sequence Triple- helical structure

Hydroxyproline & Hydroxylysine

Glycosylation

Amino Acid Sequence: Collagen is a glycoprotein

containing galactose and glucose as the carbohydrate content.

Glycine is one - third of total amino acid content of collagen followed by hydroxyproline and proline account for another one-third of amino acid content of collagen.

Proline - facilitate the formation of helical conformation of α- chain, because its ring structure causes kink in the peptide chain.

Glycine- found in every third position of the polypeptide chain. It fits into the restricted spaces where the three chains of the helix come together.

Glycine is the part of the repeating

sequence.

Gly- X-Y

X- is frequently proline

Y- hydroxy proline or hydroxylysine.

Gly-Pro-Y is most often Non-polar

Gly-X-Y is most often Polar

TRIPLE- HELICAL STRUCTURE

Amino acids side chains are on the surface

of the triple helical molecule.

This allows bond formation between the

exposed R- groups of neighboring collagen

monomers- This leads to aggregation into

fibrils.

HYDROXYPROLINE & HYDROXYLYSINE

Hydroxylation of

Proline & lysine

residues after their

incorporation into the

polypeptide chains.

Thus called post

translational

modification.

Causes stabilization of

triple helical structure.

GLYCOSYLATION Hydroxyl group of hydroxylysine residues of

collagen are enzymatically glycosylated.

Most commonly glucose and galactose are

attached.

BIOSYNTHESIS OF COLLAGEN

Precursors: Collagen is one of the proteins that functions

outside the cell.

Polypeptide Precursors of the collagen molecule are formed in Fibroblast, osteoblasts and chondroblasts.

These are secreted into the extracellular matrix.

1. Formation of Pro- α-chains: Pre-pro α-chains- contain a special amino acid sequence at their N-

terminal.

This sequence acts as a signal that the newly synthesized polypepetide is

destined for function out side the cell.

This sequence facilitate the binding of ribosomes to the rough

endoplasmic reticulum (RER), and direct the Pre-pro α-chain into the

lumen of the RER.

This sequence is cleaved in the lumen of RER and after its cleavage

Precursor of collagen is formed.

This precursor is called Pro α-chain.

2. Hydroxylation:

Processing of Pro α-chains occur by a number of enzymic

steps in the lumen of RER, while the polypeptides are

still being synthesized.

Proline and lysine residues are hydroxylated.

This reaction requires O2 and vitamin C.

Enzymes are prolyl hydroxylase and lysyl hydroxylase.

In Vit C deficiency, collagen fibers cannot cross link- and

tensile strength is decreased (scurvy).

3. Glycosylation: Modified by glycosylation with glucose or

galactose residues.

4. Assembly and Secretion: After hydroxylation and glycosylation- Pro α-

chains are converted to Pro-collagen. Pro-collagen has a central region of triple

helix and its ends have non-helical regions of amino and carboxyl terminal extensions .

These extensions are called Propeptides.

In the formation of procollagen interchain disulfide bonds are formed between the C- terminal extensions of the pro α-chains.

This alignment of pro α-chains is favorable for helix formation

Then pro-collagen chains are translocated to Golgi- apparatus.

In the golgi they are packaged in secretory vesicles.

These vesicles fuse with the membrane and release the pro-collagen molecule into the extracellular space.

5. Extracellular cleavage of Procollagen molecules:

After their release the Procollagen molecules are cleaved by N- and C Procollagen peptidases.

These remove the terminal Propeptides.

Triple helical structure is released as Tropocollagen

6. Formation of collagen fibrils: Tropocollagen spontaneously associate with each

other and form collagen fibrils.

7. Cross-link formation: The fibrils that are formed become a substrate

for lysyl oxidase. It contains copper. It oxidatively deaminates lysyl and hydroxlysyl

residues in collagen. Reactive aldehydes- Allysine and

hydroxylysine are formed. These aldehydes the react with the

neighboring lysyl and hydroxlysyl and covalent cross links are formed.

This cross-linking leads to the formation of mature collagen.

Steps involved in collagen biosynthesis

Rough Endoplasmic Reticulum₪ Synthesis of preprocollagen₪ Insertion of procollagen molecule into the lumen of ER.

Lumen of ER: ₪ Hydroxylation of proline and lysine residues.₪ Glycosylation of selected hydroxylysine residues.

Lumen of ER and Golgi apparatus: ₪ Self assembly of tropocollagen molecule (disulfide bond

formation).

Secretory vesicles:

USES Cardiac applications Cosmetic surgery Bone grafts Tissue regeneration Reconstructive

surgical uses Wound care

management uses

Degradation of collagen: Collagen highly stable molecule.Half life is several years.Breakdown- collagenases

Collagen diseases

Ehlers- Danlos Syndrome

Scurvy Osteogenesis Imperfecta syndrome.ChondrodysplasiasAlport syndromeOsteoporosisKnobloch syndrome  

Osteogenesis Imperfecta syndrome

PROTEIN ADHESIVES

An adhesive is a material used for

holding two surfaces together. An

adhesive must wet the surfaces, adhere

to the surfaces, develop strength after it

has been applied, and remain stable.

Adhesion is a specific interfacial

phenomenon. There are three main

theories of adhesion: adsorption,

electrical and diffusion. All probably

apply to most adhesives.

æ Protein Adhesives are mixtures of various types of plant or animal-based proteins with other additives. These adhesives come in cake form, liquid or dry flakes. The cake form has water already mixed with it for immediate as-is use when heated in an applicating device and can be formulated for tack and speed set properties. The liquid and flake forms are often mixed with water up to 50% at the end-user’s facility to give the customer options for various applications and substrates. The adhesive is heated to approx 140° F and applied.

æ Protein Adhesives provide:o Flexibility of adhesive filmo Excellent non-warp characteristicso Permanent adhesiono Ease of clean-upo Non-hazardous, non-toxic, biodegradable

Protein adhesives are also called cake or jelly glues 

A variety of organisms form protein based adhesives essential to their survival.

Eg Marine mussels and barnacles ,insects ,and spiders

Many other organisms also produce unusual adhesive like protein, glycoproteins,and polysaccharide that that await characterization.

Protein based adhesives are biodegradabile,are able to set or cure in wet environment, and adhere to surface of rocks and other under water substrate, have been most extensively studied.

The mussel adhesive contain fibers,fillers,and catalyst in a cross linked resin.

There is a wide range of products are used. proteins which are derived from the hydrolysis of either

collagen or soya flour, or by separating casein from skim milk. Animal glues from bones and hides are used in gummed tape,

textiles The paper industry such as book-binding and case making. Fish glues manufactured from skins have been used in rubber

gasket to steel bonding, paper to steel etc. Caseirs from skim milk are used mainly in wood to wood

bonds. Soya bean glues are used in paper backs. Blood glues are mainly used in veneering and plywood.

ANIMAL GLUE

An animal glue is an adhesive that is created by prolonged boiling of animal connective tissue.

These protein colloid glues are formed through hydrolysis of the collagen from skins, bones, tendons, and other tissues, similar to gelatin. These proteins form a molecular bond with the glued object.

MODERN USES used for making and restoring objects, paintings, illuminated parchment

manuscripts, and other artifacts.Gelatin, a form of animal glue, is found in many contemporary products, such as gelatin desserts, marshmallows, and pharmaceutical capsules, and is used to reinforce sinew wrappings, wood, leather, bark, and paper.

This adhesive is mostly used as glue, sizing, or varnish, although it is not as frequently used as other adhesives because it is water soluble. Other aspects, such as difficulty of storage in a wet state, requirement for fresh raw materials make this product more difficult to find and use.

Animal glues will also darken with age and shrink as they dry, giving them the potential to harm wood, paper, or works of art. Too much handling and too many changes in temperature or humidity could cause further harm.

Currently there is controversy into the production and use of hide glue, particularly because most animal glue industries prefer using cattle and horses and thus encourage the slaughter of these animals.

TYPES AND USES☺ Animal glue was the most common woodworking glue. ☺ lutherie ☺ pipe organ building☺ piano repairs, ☺ antique restoration. ☺ Glass artists take advantage of hide glue's ability to bond with glass,

applying hide glue to glass. ☺ As the glue hardens it shrinks, chipping the glass.☺ It has several advantages and disadvantages compared to other glues. The

glue is applied hot, typically with a brush or spatula. Glue is kept hot in a glue pot, which may be an electric unit built for the purpose, a double boiler, or simply a saucepan or crock pot to provide a warm water bath for the container of glue.

☺ Most animal glues are soluble in water, useful for joints which may at some time need to be separated.Alcohol is sometimes applied to such joints to dehydrate the glue, making it more brittle and easier to crack apart.

GELATIN gelatin,  animal protein substance having gel-forming

properties, used primarily in food products and home cookery, also having various industrial uses.

Derived from collagen it is extracted by boiling animal hides, skins, bones, and

tissue after alkali or acid pretreatment. it is nutritionally an incomplete protein, deficient in

certain amino acids. Unflavored, granulated gelatin, almost tasteless and

odorless, ranges from faint yellow to amber in colour. Immersed in a liquid, gelatin takes up moisture and swells. When the liquid is warmed, the swollen particles melt,

forming a sol (fluid colloidal system) with the liquid that increases in viscosity and solidifies to form a gel as it cools.

The gel state is reversible to a sol state at higher temperatures, and the sol can be changed back to a gel by cooling

Capsule made of gelatin

Gelatin may be whipped to form a foam and acts as an emulsifier and stabilizer.

It is used to make such gel foods as jellied meats, soups, and candies, aspics, and molded desserts and to stabilize such emulsion and foam food products as ice cream, marshmallows, and mixtures of oils or fats with water.

Fruit jellies resemble gelatin products but achieve solidification as a result of a natural vegetable substance called pectin.

The food industry makes use of most of the gelatin produced.

Gelatin is also used by the pharmaceutical industry for the manufacture of capsules, cosmetics, ointments, lozenges, and plasma products and by other industries.

Actin

Actin is a globular multi-functional protein that forms microfilaments. It is found in all eukaryotic cells (the only known exception being nematode sperm)

It is highly conserved and participates in more protein-protein interactions than any known protein.

overall dimensions 67*40*37 A

The globular actin is often called G-actin. It contains a nucleotide-binding site, which can bind to ATP or ADP.

The conformation of actin depends on the ATP or ADP in the nucleotide-binding site.

Actin filament is often called F-actin. It is twisted helical chains of actins, which the actin monomers orient in the same direction of actin filament.

It has polarity that contains different ends in its structure. One end is called barbed (+) while the other end is called pointed (-).

Some major roles of actin include:

(1) Being the structural makeup and support of the cytoskeleton.

(2) Dividing and producing cells in order to enable cells to move spontaneously and actively.

(3) Serving as a supportive framework for myosin proteins during muscle contraction.

(4) Acting as a track for the cargo transport myosins in non-muscle cells.

Applications

Actin is used in scientific and technological laboratories as a track for molecular motors such as myosin (either in muscle tissue or outside it) and as a necessary component for cellular functioning.

It can also be used as a diagnostic tool In Nanotechnology it could be used for the directed transport

of molecules for deposit in determined locations, which would permit the controlled assembly of nanostructures

Food technology. It is possible to determine the quality of certain processed foods, such as sausages

Health. Some alleles of actin cause diseases; for this reason techniques for their detection have been developed. In addition, actin can be used as an indirect marker in surgical pathology.

Dystrophin

Dystrophin is a rod-shaped cytoplasmic protein, and a

vital part of a protein complex that connects

the cytoskeleton of a muscle fiber to the

surrounding extracellular matrix through the cell

membrane.

This complex is variously known as the costamere or

the dystrophin-associated protein complex.

Many muscle proteins, such as α

dystrobrevin, syncoilin,synemin, sarcoglycan, dystroglycan,

and sarcospan, colocalize with dystrophin at the costamere.

The dystrophin gene is one of the longest human genes

known, covering 2.5 megabases (0.08% of the human

genome) at locus Xp21

Function It is a cohesive protein, linking actin filaments to another

support protein that resides on the inside surface of each muscle fiber’s plasma membrane (sarcolemma).

This support protein on the inside surface of the sarcolemma in turn links to two other consecutive proteins for a total of three linking proteins.

The final linking protein is attached to the fibrous endomysium of the entire muscle fiber.

Dystrophin supports muscle fiber strength, reduces muscle stiffness, increases sarcolemmal deformability, and compromises the

mechanical stability of costameres and their connections to nearby myofibrils;

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