BETA-TURNS IN NASCENT PROCOLLAGEN ARE SITES OF POSTTRANSLATIONAL ENZYMATIC HYDROXYLATION OF PROLINE

The selective hydroxylation of proline residues in nascent procollagen chains by prolyl hydroxylase (EC 1.14.11.2) can be understood in terms of the conformational feature of the -Pro-Gly- segments in linear peptides and globular proteins. The folded .beta.-turn conformation in such segments appears to be the conformational requirement for proline hydroxylation. The available data on the hydroxylation of native and synthetic substrates of prolyl hydroxylase are explained on the basis of the extent of .beta.-turn formation in them. Taken in conjunction with the conformational features of the hydroxyproline residue, the results bring out the conformational reason for the posttranslational proline hydroxylation which may lead to the straightening of the .beta.-turn segments into the linear triple-helical conformation.