Some science behind the scenes
(2S,4R)-4-Hydroxyproline, or L-hydroxyproline (C5H9O3N), is a common non-proteinogenic amino acid. It was discovered in 1902, by Hermann Emil Fischer who isolated hydroxyproline from hydrolyzed gelatine. This should give us a clue as to one of its main roles.
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.
Another very important use for hydroxyproline is in forming elastin. Elastin is just as important as collagen in the human body. Elastin is a highly elastic protein in connective tissue and enables tissues in the body to resume their shape after stretching or contracting. Elastin helps skin to return to its original position when it is poked or pinched. Elastin is also an important load-bearing tissue in the bodies of vertebrates and used in places where mechanical energy is required to be stored.
Hydroxyproline is produced in the body by hydroxylation of the amino acid proline by the enzyme prolyl hydroxylase following protein synthesis (as a post-translational modification).
But it also occurs in plants, as such if this enzyme is deficient in any way, then it is useful to know the plant sources for this essential building block.
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