Everything about Hydroxyproline totally explained
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4-Hydroxyproline, or hydroxyproline (
C5H9O3N), is an uncommon
amino acid, abbreviated as
HYP, for example, in
Protein Data Bank.
Structure
Hydroxyproline differs from
proline by the presence of a hydroxyl (OH) group attached to the C (gamma) atom.
Other hydroxyprolines also exist in nature, notably
2,3-cis-3,4-trans-3,4-dihydroxyproline which occurs in
diatom cell walls and is postulated to have a role in
silica deposition. Hydroxyproline is also found in the walls of
oomycetes, fungus-like protists related to diatoms.
Production and function
Hydroxyproline is produced by
hydroxylation of the amino acid
proline by the enzyme
prolyl hydroxylase following protein synthesis (as a
post-translational modification). The enzyme catalysed reaction takes place in the lumen of the endoplasmic reticulum.
Hydroxyproline is a major component of the
protein collagen. Hydroxyproline and proline play key roles for collagen stability. They permit the sharp twisting of the collagen helix. 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. This modification of the proline residue increases the stability of the collagen triple helix. It was initially proposed that the stabilization was due to water molecules forming a hydrogen bonding network linking the prolyl hydroxyl groups and the main-chain carbonyl groups. It was subsequently shown that the increase in stability is primarily through stereoelectronic effects and that hydration of the hydroxyproline residues provides little or no additional stability.
Hydroxyproline is found in few proteins other than collagen. The only other
mammalian protein which includes hydroxyproline is
elastin. For this reason, hydroxyproline content has been used as an indicator to determine
collagen and/or
gelatin amount.
Clinical significance
Proline hydroxylation requires
ascorbic acid. The most obvious, first effects (gum and hair problems) of absence of
ascorbic acid in humans come from the resulting defect in
hydroxylation of
proline residues of
collagen, with reduced
stability of the collagen molecule causing
scurvy.
Further Information
Get more info on 'Hydroxyproline'.
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