In collagen, helical collagen , or helix-type , is the main form in the secondary structure. It consists of a triple helix made of glycine sequence of recurrent amino acids - X - Y, where X and Y are often proline or hydroxyproline. Triple helix collagen has 3.3 residues per turn. Each of the three chains is stabilized by steric repulsion due to pyrrolidine proline rings and hydroxyproline residues. Pyrrolidine rings keep from one another's way when the polypeptide chain assumes this extended helical shape, which is much more open than the circular shape of the alpha helix. The three chains are hydrogen bound to one another. The hydrogen bond donor is the NH group of peptide glycine residues. The hydrogen bond acceptor is the CO group of residues on another chain. The OH hydroxyproline group also participates in hydrogen bonding. The emergence of collagen (superhelix) helix is ​​2.9 Æ'... (0.29 nm) per residue.
Video Collagen helix
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Source of the article : Wikipedia
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