Collagen

The connective tissue protein

Why study tissue proteins?

To understand normal body functions . In development In inflammatory states Aging process.

To identify the cause of various genetic and metabolic disorders related to tissue proteins

In the spread of cancer cells. Several diseases (eg:Osteogenesis imperfecta and a number of types of the

Ehlers-Danlos syndrome) are due to genetic disturbances of the synthesis of collagen.

Components of proteoglycans are affected in the group of genetic disorders known as the mucopolysaccharidoses.

To use and apply them in the medical, industrial, commercial fields. In food products, cosmetic surgery. The gelatin used in food and industry is derived from the partial hydrolysis of

collagen.

The Extracellular Matrix The space outside the cells of a tissue is filled with a composite material

called extracellular matrix(ECM). This ECM is also known as the connective tissue. It is composed of -

a) Gel with interstitial fluid.

b) 3 major classes of biomolecules: Structural proteins: collagen, elastin and Keratin(epidermal tissues) Specialized proteins: e.g. fibrillin, fibronectin, and laminin. Proteoglycans(Mucoproteins) : Conjugated proteins consisting of

Protein + Carbohydrate(5%-95%) Carbohydrate part is in the form of Glycosaminoglycans [GAGs].

Thus, the extracellular matrix (ECM) is a complex structural entity surrounding and supporting cells that are found within mammalian tissues.

The Extra cellular matrix

Collagen Most abundant insoluble fibrous protein in the connective tissue of mammals. Makes up about 25% to 35% of the whole-body protein content. Scleroprotein secreted from the cells called fibroblasts. In greek ‘kolla’ means ‘glue’.Collagen is also called as glue-producer. Distribution of collagen varies in different tissues.

Also found in mucous membranes, nerves,Blood vessels, and organs.

90%

85%

70%4%

bones tendonsskin liver

Collagen fibers in muscle tendons

Functions Of Collagen

It imparts strength, support, shape and elasicity to the tissues. It accounts for 6% of the weight

of strong, tendinous muscles It provides flexibility, support, and

movement to cartilage. It encases and protects delicate

organs like kidneys and spleen. It fills the sclera of the eye in

crystalline form. Teeth(dentin) are made by adding

mineral crystals to collagen. Collagen contributes to proper

alignment of cells for cell proliferation and differentiation.

When exposed in damaged blood vessels, it initiates thrombus formation

Types Of Collagen In humans, there are at least 19

distinct types of collagen made up of 30 distinct polypeptide chains (each encoded by a separate gene).

They are subdivided into a number of classes based primarily on the structures they form

However, 90% of the collagen in the body are of type I, II, III, and IV.

These types determine the physical properties of specific tissues and perform their specialized function.

Structure Of CollagenThe basic structural unit of a

collagen molecule is a triple helix.Triple helical structure may occur

throughout the molecule or only in a part of it.

Structure Of type I mature Collagen: Triple helical structure occurs

throughout the molecule.

This triple helix is composed of 3 polypeptide chains twisted around each other.

Each polypeptide/alpha chain is in turn a left handed helix with 3 amino acids per turn totally containing approximately 1000 amino acids per chain.

Alpha chain Triple Helix

Amino-acids

Each alpha chain has an unusual abundance of 3 amino-acids glycine, proline and hydroxyproline.

Glycine occurs at every third position in the amino acid sequence which can be represented as (Gly-X-Y)n.

X and Y are other amino acids of which proline and hydroxyproline occupy 100 positions each.

Glycine occupies the crowded center of the triple helix as it has a small side chain[ H atom] where as Hydroxyproline and proline point outwards imparting rigidity to the triple helix.

The alpha chains are wound around each other in a right handed super helix to form a rod like molecule 1.4nm wide and 300nm long

[Gly-X-Y]n

The triple helices are stabilized by Hydrogen bonds, covalent cross-links, electrostatic and hydrophobic interactions and van der waals forces.

The covalent cross links within and between the helices are formed by copper dependent enzyme lysyl oxidase between the lysine and hydroxylysine residues.

These triple helical molecules pack together side by side to form elongated fibrils.

Fibrils are displaced longitudinally from each other by 67 nm [one quatter of its length] to form a quarter staggered arrangement.

Fibrils bundle up to form fibers making up tissues.

Cross link formation

Structure of collagen fibers

Biosynthesis of Collagen Collagen synthesis occurs in the fibroblasts, osteoblasts in bone,

chondroblasts in cartilage and odontoblasts in teeth. First synthesized in precursor form of preprocollagen polypeptide chain

in the ribosomes during translation The leader sequence of amino acids[signal peptide] in the

preprocollagen directs it to enter the lumen of E.R In the lumen of E.R, the Signal peptide is cleaved to form procollagen. The proline and lysine amino acids in the procollagen chain undergo

hydroxylation and glycosylation known as post translational modifications.

Disulfide bonds are formed between three procollagen chains which twist around each other to form a triple helix molecule.This step is called registration.

This Procollagen molecule is secreted into the extracellular matrix from the golgi compartment of the E.R.

Here, the procollagen aminoproteinase and carboxy proteinase enzymes remove extra terminal amino acids from the procollagen molecule to form collagen .

The collagen molecules assemble into fibrils and inturn fibers being stabilized by the covalent cross-links.

Biosynthesis of collagen from Preprocollagen

Synthesis Of Collagen

Abnormalities associated with collagen

Collagen-related diseases arise from genetic defects nutritional deficiencies

They affect the biosynthesis, assembly, postranslational modification, secretion, or other processes involved in normal collagen production.

These include : Ehler Danlos syndrome Alport syndrome Epidermolysis bullosa Osteogenesis Imperfecta Chondrodysplasias [affects cartilage] Scurvy Osteolathyrism

Ehler Danlos Syndrome Ehlers-Danlos Syndrome is a group of inherited connective tissue disorders. CAUSE

abnormalities in the synthesis and metabolism of collagen Mutations in the collagen genes: COL1A1, COL1A2, COL3A1, COL5A1, COL5A2 a deficiency of enzyme lysyl hydroxylase. A deficiency of procollagenN-proteinase, causing formation of abnormal thin,

irregular collagen fibrils EFFECT

Mutations alter the structure, production, or processing of collagen or proteins that interact with collagen

WeakenS connective tissue in the skin, bones, blood vessels, and organs causing- Skin hyperextensibility Joint dislocations Tissue fragility Poor wound healing.

Ehler-Danlos Syndrome

• Hyperextensibility of skin

• Hypermobility of joints

Alport Syndrome Alport syndrome is a genetic disorder

characterized by glomerulonephritis, endstage kidney disease, and hearing loss. It also affects the eyes. The presence of blood in the

urine[hematuria] is almost always found in this condition.

CAUSE Mutations in COL4A3,COL4A4,COL4A5

collagen biosynthesis genes. These prevent the production or

assembly of the type IV collagen network in the basement membranes.

kidneys are scarred and unable to filter waste products resulting in hematuria and renal disease.

Alport syndrome affecting eyes

Epidermolysis Bullosa• Epidermolysis bullosa refers to a group of

inherited disorders that involve the formation of blisters following trivial trauma.

• CAUSE mutations in COL7A1, affecting the

structure of type VII collagen. Type VII collagen forms delicate fibrils

that anchor the basal lamina to collagen fibrils in the dermis.

These anchoring fibrils are reduced in this form of the disease, causing friction and blistering.

• EFFECT Blistering and painful sores like third

degree burns

Blister formation

Osteogenesis Imperfecta Osteogenesis imperfecta or Brittle Bone Disease is a

genetic bone disorder due to decrease dcollagen formation.

CAUSE Mutations in the COL1A1 andCOL1A2 genes

coding for procollagen chains. Replacement of glycine by another bulkier amino

acid resulting in decreased collagen or improper procollagen structure forming abnormal fibers.

Mutations also cause ‘procollagen suicide ‘ All these cause brittleness.

EFFECT Thin,t ransclucent, blue scleras. Affected infants may be born with multiple

fractures and not survive. weak muscles, brittle teeth, a curved spine and

hearing loss.

Chondrodysplasias Chondrodysplasias are a mixed

group of hereditary disorders affecting cartilage.

One example is Stickler syndrome, manifested by degeneration of joint cartilage and of the vitreous body of the eye.

CAUSE Mutations in the COL2A1

gene, leading to abnormal forms of type II collagen.

EFFECT shortlimbed dwarfism skeletal deformities.

Osteolathyrism Osteolathyrism is a collagen cross-linking

deficiency caused by dietary over-reliance on the seeds of Lathyrus sativus (kesari dal) in some parts of India.

CAUSE Osteolathyrogenic compounds like Beta-

aminopropionitrile(BAPN) and Beta-oxalyl aminoalanine [BOAA] found in Kesari dhal inhibit enzyme lysyl oxidase required for the formation of cross links in the triple helices

EFFECT weakness and fragility of skin, bones, and

blood vessels Paralysis of the lower extremities

associated with neurolathyrism

Scurvy Scurvy is a disease due to deficiency of

vitamin C It is not a genetic disease. It is related to improper collagen

formation CAUSE

Vitamin C [ascorbic acid ]is required as a cofactor for hydroxylase enzymes during the hydroxylation of proline and lysine in the synthesis of collagen.

Deficiency causes impaired collagen synthesis due to deficiency of hydroxylases.

EFFECT Bleeding of gums Poor wound healing Subcutaneous hemorrhages

Uses Of Collagen Industrial Uses

Collagen is used as temporary thermoplastic glues in musical instruments like violin and guitar .

Recently used as a fertilizer Gelatin derived from the partial hydrolysis of collagen is used in food products

like desserts, jellies. It is also used in pharmaceutical, cosmetic, and photography industries.

Medical uses Mild benefit to rheumatoid arthritis patients. Keeps the valvular leaflets of heart in shape. Helps in the deposition of calcium during aging. Used in cosmetic surgery, for burn patients for reconstruction of bone and a

wide variety of dental, orthopedic and surgical purposes. Main ingredient of cosmetic makeup. Human collagen is used for immunosuppression during transplantation.