Stereochemistry of the pyrrolidine rings in the collagen structure

Abstract

In the collagen triple-helical structure, large side groups occuring at location 3 in the repeating triplet sequences (Gly-R_z-R_z)n are appreciably constrained if a proline residue occurs as R₂ in a neighbouring chain. The severity of the steric hindrance depends on the geometry of the prolyl ring. In this paper we propose two different puckerings for the proline ring, the first one being energetically favorable for most types of residue sequences commonly found in collegen while the second is preferable when an amino acid residue with a large side group occurs at location 3 in a neighbouring chain. The puckering of the pyrrolidine ring of hydroxyproline, as proposed earlier, is quite favorable from energy as well as stereochemical considerations.