Collagen

Collagen is the major component of the connective tissue of most animals and the most abundant vertebrate protein, consistuting about 25% to 35% of the total protein in mammals. There are at least 15 different types of collagen preteins. Native collagen is a molecule consisting of three chains having left-handed helices coiled around each other to form a right-handed supercoil. The collagen supercoil is stabilized by interchain hydrogen bonding and by the opposing twist of the helices and the supercoil.There are no intrachain hydrogen bonds in the collagen helix.

A typical collagen molecule is a rod 300 nm long and 1.5nm in diameter. Collagen helices typically contain glycine residues in every third position. Characteristic of collagen is the repeating sequence -Gly-X-Y- , where X is often proline and Y is often 4-hydroxyproline (Hyp). For each -Gly-X-Y- triplet, one intermolecular hydrogen bond forms between the amide hydrogen atom of a glycine in one chain and the carboonyl oxygen atom of residue X in an adjacent chain.