7/2-Helical model for collagen - Evidence from model peptides

摘要

After about fifty years since the prediction of a triple-helical structure, there are still two models for collagen with different helical symmetry. One is the Rich and Crick model in which three strands form a left-handed 10/3-helix with an axial repeat of 28.6A. The other is the Okuyama model in which three strands form a left- handed 7/2-helix with an axial repeat of 20A. High-resolution structures of collagen model peptides (Pro-Pro-Gly)10 and (Pro-Hyp-Gly)10 strongly support the latter model. The comparison of water molecules found in these strutures, together with the water bridges involving the hydroxyl group of Hyp, indicated that water molecules do not contribute to the extra stability of the triple-helix as has been considered for many years. This observation agreed well with a recent finding that the extra stability of collagen with Hyp at the Y-position is due to the inductive effects rather than water bridges involving hydroxyl groups .