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Hydroxyproline and proline play key roles for collagen stability. [4] They permit the sharp twisting of the collagen helix. [ 5 ] In the canonical collagen Xaa-Yaa-Gly triad (where Xaa and Yaa are any amino acid), a proline occupying the Yaa position is hydroxylated to give a Xaa-Hyp-Gly sequence.
Procollagen-proline dioxygenase catalyzes the following reaction: L-proline + alpha-ketoglutaric acid + O 2 → (2S, 4R)-4-hydroxyproline + succinate + CO 2. The mechanism for the reaction is similar to that of other dioxygenases, and occurs in two distinct stages: [3] In the first, a highly reactive Fe(IV)=O species is produced.
Proline or hydroxyproline constitute about 1/6 of the total sequence. With glycine accounting for the 1/3 of the sequence, this means approximately half of the collagen sequence is not glycine, proline or hydroxyproline, a fact often missed due to the distraction of the unusual GX 1 X 2 character of collagen alpha
In 1954, Ramachandran & Kartha (13, 14) advanced a structure for the collagen triple helix on the basis of fiber diffraction data. It consists of a triple helix made of the repetitious amino acid sequence glycine-X-Y, where X and Y are frequently proline or hydroxyproline. [2] [3] Collagen folded into a triple helix is known as tropocollagen.
The cyclic structure of proline's side chain locks the angle φ at approximately −65°. [19] Proline acts as a structural disruptor in the middle of regular secondary structure elements such as alpha helices and beta sheets; however, proline is commonly found as the first residue of an alpha helix and also in the edge strands of beta sheets.
This (Gly-X-Y)n sequence is repeated 343 times in the type III collagen molecule. Proline or hydroxyproline is often found in the X- and Y-position giving the triple helix stability. In addition to being an integral structural component of many organs, type III collagen is also an important regulator of the diameter of type I and II collagen ...
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