Hydroxyproline

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ImageFile = Hydroxyproline structure.svg
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IUPACName = (2S,4R)-4-hydroxypyrrolidine-
2-carboxylic acid
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Section1 = Chembox Identifiers
CASNo = 51-35-4
PubChem = 825
SMILES = OC1CNC(C1)C(O)=O
MeSHName = Hydroxyproline
Section2 = Chembox Properties
Formula = C₅H₉NO₃
MolarMass = 131.13
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4-Hydroxyproline, or hydroxyproline (C₅H₉O₃N), is an uncommon amino acid, abbreviated as HYP, e.g., in Protein Data Bank.

tructure

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 wallsNakajima, T. and Volcani, B.E. (1969). 3,4-Dihydroxyproline: a new amino acid in diatom cell walls. Science, 164, 1400-1401. PMID 5783709] 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.Alexopoulos, C.J., Mims C.W. and Blackwell, M.(1996). "Introductory Mycology", 4th ed., p. 687-688. (New York: John Wiley & Sons). ISBN 0-471-52229-5.]

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.Nelson, D. L. and Cox, M. M. (2005) Lehninger's Principles of Biochemistry, 4th Edition, W. H. Freeman and Company, New York.] They permit the sharp twisting of the collagen helix.Brinckmann, J., Notbohm, H. and Müller, P.K. (2005) Collagen, Topics in Current Chemistry 247, Springer, Berlin.] 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.Bella, J., Eaton, M., Brodsky, B. and Berman, H.M. (1994). Science 266, 75-81. PMID 7695699] 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.Kotch F.W., Guzei I.A. and Raines R.T. (2008). Stabilization of the collagen triple helix by O-methylation of hydroxyproline residues. Journal of the American Chemical Society, 130, 2952-2953. PMID 18271593]

Hydroxyproline is found in few proteins other than collagen. The only other mammalian protein which includes hydroxyproline is elastin.Ward, A. G. and Courts, A. (1977) The Science and Technology of Gelatin, Academic Press, New York.] 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.

ee also

* Imino acid
*Hydroxylysine

External links

* [https://simtk.org/home/hydroxyproline Molecular mechanics parameters]

References

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