Hydroxyproline
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2008-06-26T09:12:27Z
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| ImageFile = Hydroxyproline structure.svg
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| IUPACName = (2S,4R)-4-hydroxypyrrolidine-<br>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 = C<sub>5</sub>H<sub>9</sub>NO<sub>3</sub>
| MolarMass = 131.13
| Appearance =
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| Section3 = {{Chembox Hazards
| Solubility =
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'''4-Hydroxyproline''', or hydroxyproline ([[Carbon|C]]<sub>5</sub>[[Hydrogen|H]]<sub>9</sub>[[Oxygen|O]]<sub>3</sub>[[Nitrogen|N]]), is an uncommon [[amino acid]], abbreviated as '''HYP''', e.g., 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 wall]]s<ref name="Nakajima">Nakajima, T. and Volcani, B.E. (1969). 3,4-Dihydroxyproline: a new amino acid in diatom cell walls. Science, 164, 1400-1401. PMID 5783709</ref> and is postulated to have a role in [[silica]] deposition. Hydroxyproline is also found in the walls of [[oomycete]]s, fungus-like protists related to diatoms.<ref name="Alexopoulos 1996">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.</ref>
==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.<ref name=''Nelson''>Nelson, D. L. and Cox, M. M. (2005) Lehninger's Principles of Biochemistry, 4th Edition, W. H. Freeman and Company, New York.</ref> They permit the sharp twisting of the collagen helix.<ref name=''Brinckmann''>Brinckmann, J., Notbohm, H. and Müller, P.K. (2005) Collagen, Topics in Current Chemistry 247, Springer, Berlin.</ref> 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.<ref name=Bella1994>Bella, J., Eaton, M., Brodsky, B. and Berman, H.M. (1994). Science 266, 75-81. PMID 7695699</ref> It was subsequently shown that the increase in stability is primarily through [[stereoelectronic effect]]s and that hydration of the hydroxyproline residues provides little or no additional stability.<ref name=Kotch2008>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</ref>
Hydroxyproline is found in few proteins other than collagen. The only other [[mammalian]] protein which includes hydroxyproline is [[elastin]].<ref name=''Ward''>Ward, A. G. and Courts, A. (1977) The Science and Technology of Gelatin, Academic Press, New York.</ref> 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]].
==See also==
* [[Imino acid]]
*[[Hydroxylysine]]
== External links ==
* [https://simtk.org/home/hydroxyproline Molecular mechanics parameters]
== References ==
<div class="references-small">
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==Additional images==
<gallery>
Image:L-proline-skeletal.png|[[proline]]
</gallery>
[[Category:Cyclic amino acids]]
[[de:Hydroxyprolin]]
[[fr:Hydroxyproline]]
[[ja:ヒドロキシプロリン]]
[[pl:Hydroksyprolina]]