Glycine collagen structure

Figure 2.20. Models of collagen structure. (A) Model of three parallel left-handed helixes of collagen showing the location of Coc (C) for chains A, B, and C. Note all glycines are found in C-l position because this is the only amino acid residue that can be accommodated at the center of the triple helix. Later studies by Ramachan-dran and co-workers indicated that the three chains are wrapped around each other (B) in a right-handed superhelix. The axial rise per residue is 0.29 nm, and the axial displacement of different Coc atoms is shown in parentheses in angstroms.

Collagen Collagen is an extracellular structural protein 1052 amino acid residues. Collagen has an minsnal amino acid composidon it is about one-third glycine and is rich in proline. Note diat it also lacks Cys and Trp and is deficient in aromadc amino acid residues in general. 

Fig. 4. Helical structure of collagen, typical amino acid sequence within a collagen strand, and exchangeable versus non-exchangeable hydrogen atoms in an individual leucine molecule (Gly - glycine. Pro - Proline, Leu - leucine. Hyp - hydroxyproline.

The many (possibly more than 30) types of collagens found in human connective tissues have substantially the same chemical structure consisting mainly of glycine with smaller amounts of proline and some lysine and alanine. In addition, there are two unusual amino acids, hydroxyproline and hydroxylysine, neither of which has a corresponding base-triplet or codon within the genetic code. There is therefore, extensive post-translational modification of the protein by hydroxylation and also by glycosylation reactions. 

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