Collagen

It is a type of structural protein which is most abundant protein in the human body . It is found throughout the body . It is the main fibrous component of skin , tendon,bone and cartilage. Normal collagen denatures at 39 c and on boiling they yield gelatin .Vertebrates have 46 genetically distinct polypeptide chains comprising 28 distinct collagen types . it is a secreted protein and therefore occurs outside cells. They are hydrolyzed by pepsin Enzyme. 

Structure -triple helix structure (3.3  aminoacids residues per turn )

• Collagens are made up of 3 polypeptide alpha chains which are left handed and coiled around each other to form a right alpha helix confirmation . 
• Each such helix is around 1.4 nm in diameter and 300 nm in length . The rise of the collagen helix (superhelix) is 2.9 Å (0.29 nm) per residue. 
• Glycine occupies every third position in the repeating amino acid sequence. (Gly-X-Y). X is often proline. Proline makes up about 17% of collagen.
• Collagen contains two uncommon derivative amino acids . These amino acids are found at specific locations relative to glycine and are modified post-translationally by different enzymes, both of which require vitamin-C as a co-factor-
• 1.Hydroxyproline derived from proline .     2. Hydroxylysine derived from lysine.
• Proline and hydroxyproline residues permit sharp twisting of collagen helix.Only glycine residues can be accomodated at tight junctions between chains.

Formation of fibril -

1.After the formation of alpha chain the sequence facilitate binding of ribosomes to the rough ER and direct the alpha chain into the lumen of the RER.

2.This sequence is cleaved and precurser of collagen Pro- alpha chain is formed.
3.Proline and lysine are hydrolysed and modified by glycosylation with glucose or galactose residues.

4.After hydroxylation and glycosylation pro alpha chains are converted to pro -collagen .

5.Pro collagens are translocated to Golgi - apparatus .

6.In the golgi apparatus they are packaged in secretory vesicles or transport vesicles (Exocytosis).

7.Vesicles fuse with the membrane and release the pro- collagen into extracellular space.

8. Procollagen molecules are cleaved by N and C pro collagen peptides.

9.Triple helical structure is released as Tropocollagen .

10.Tropocollagen spontaneously associate with each other and form collagen fibrils .
Thank you for visiting my blog.Please feel free to share your comment on this article ,Please subscribe and share the articles to get more such articles.