CONFORMATIONAL VARIABILITY OF GLY-GLY SEGMENTS IN PEPTIDES - A COMPARISON OF THE CRYSTAL STRUCTURES OF AN ACYCLIC PENTAPEPTIDE AND AN OCTAPEPTIDE

摘要

The crystal structure of an acyclic pentapeptide, Boc-Gly-Gly-Leu-Aib-Val-OMe, reveals an extended conformation for the Gly-Gly segment, in contrast to the helical conformation determined earlier in the octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe. [I. L. Karle, A. Banerjee, S. Bhattacharjya, and P. Balarum [1996] Biopolymers, Vol. 38, pp. 515-526). The pentapeptide crystallizes in space group P2(1) with one molecule in the asymmetric unit. The cell parameters are: a=10.979(2) Angstrom, b=9.625(2) Angstrom, c=14.141(2) Angstrom, and beta=96.93(1)degrees, R=6.7% for 2501 reflections (I>3 sigma(I)). The Gly-Gly segment is extended (phi(1)=-92 degrees, psi(1)=-133 degrees, phi(2)-170 degrees), while the Leu-Aib segment adopts a type II beta-turn conformation (phi(3)=-61 degrees, psi(3)=130 degrees, phi(4)=71 degrees, psi(4)=6 degrees). The observed conformation for the pentapeptide permits rationalization of a structural transition observed for the octapeptide in solution. An analysis of Gly-Gly segments in peptide crystal structures shows a preference for either beta-turn or extended conformations. (C) 1997 John Wiley & Sons, Inc. [References: 16]