Hydroxyproline

Hydroxyproline
IUPAC name	(2S,4R)-4-hydroxypyrrolidine- 2-carboxylic acid
Identifiers
CAS number	51-35-4
PubChem	825
MeSH	Hydroxyproline
SMILES	OC1CNC(C1)C(O)=O
Properties
Molecular formula	C5H9NO3
Molar mass	131.13 g·mol−1
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

(2S,4R)-4-Hydroxyproline, or L-hydroxyproline (C₅H₉O₃N), is a common proteinogenic 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, the most notable ones being 2,3-cis-, 3,4-trans-, and 3,4-dihydroxyproline, which occurs in diatom cell walls^[1] 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.^[2]

Betain structure of (2S,4R)-4-hydroxyproline (left) and (2R,4S)-4-hydroxyproline (right)

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.^[3] They permit the sharp twisting of the collagen helix.^[4] 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.^[5] 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.^[6]

Hydroxyproline is found in few proteins other than collagen. The only other mammalian protein that includes hydroxyproline is elastin.^[7] 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 (vitamin C). 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

• Molecular mechanics parameters

References

Additional images

proline