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Hydroxyproline and proline play key roles for collagen stability. [4] They permit the sharp twisting of the collagen helix. [ 5 ] 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.
In 1954, Ramachandran & Kartha (13, 14) advanced a structure for the collagen triple helix on the basis of fiber diffraction data. It consists of a triple helix made of the repetitious amino acid sequence glycine-X-Y, where X and Y are frequently proline or hydroxyproline. [2] [3] Collagen folded into a triple helix is known as tropocollagen.
Due to the ring formation connected to the beta carbon, the ψ and φ angles about the peptide bond have fewer allowable degrees of rotation. As a result, it is often found in "turns" of proteins as its free entropy (ΔS) is not as comparatively large to other amino acids and thus in a folded form vs. unfolded form, the change in entropy is ...
In protein, hydroxyproline is incorporated into protein by hydroxylation of proline. Pipecolic acid, a heavier analog of proline, is found in efrapeptin. Sarcosine is a N-methylized glycine so its methyl group is used in many biochemical reactions. Azetidine-2-carboxylic acid, which is a smaller homolog of proline in plants.
Proline: P Pro Pro contains an unusual ring to the N-end amine group, which forces the CO-NH amide sequence into a fixed conformation. It can disrupt protein folding structures like α helix or β sheet, forcing the desired kink in the protein chain. Common in collagen, it often undergoes a post-translational modification to hydroxyproline ...
Hydroxylation occurs at the γ-C atom, forming hydroxyproline (Hyp), which stabilizes the secondary structure of collagen due to the strong electronegative effects of oxygen. [9] Proline hydroxylation is also a vital component of hypoxia response via hypoxia inducible factors. In some cases, proline may be hydroxylated instead on its β-C atom.
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proline. Secondary amino acids, amino acids containing a secondary amine group are sometimes named imino acids, [2] [3] though this usage is obsolescent. [1] The only proteinogenic amino acid of this type is proline, although the related non-proteinogenic amino acids hydroxyproline [4] [5] [6] and pipecolic acid [7] have often been included in studies of this class of compounds.