Hydroxyproline (Hyp)

4-Hydroxyproline, or hydroxyproline (C5H9O3N), is an uncommon amino acid, abbreviated as HYP, e.g., in Protein Data Bank.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-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.

Hydroxyproline is produced by hydroxylation of the amino acid proline by the enzyme prolyl hydroxylase following protein synthesis (as a post-translational modification).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. It helps provide stability to the triple-helical structure of collagen by forming hydrogen bonds.