FLEXIBILITY IN PEPTIDE MOLECULES AND RESTRAINTS IMPOSED BY HYDROGEN-BONDS, THE AIB RESIDUE, AND CORE INSERTS

The first segments of this article review some of the early crystal st ructure determinations of beta-bends, gamma-bends, large conformationa l changes in cyclic peptides upon complexation with metal ions, and bo th the stability and drastic change in conformation as a function of t he solvent used for growing crystals. More recent structure analyses h ave concerned helical peptides containing the Aib and/or Dpg residues and associated conformational problems such as 3(10)-/alpha-helix tran sitions, helix aberrations, reversals, severe curving of the helix, un folding, and hydration of backbone. Ion channels occurring in three cr ystal forms of zervamicin and possible ion transport and gating mechan isms are described. Finally, hydrogen bonding patterns are presented i n supramolecular assemblies of retropeptides with core inserts consist ing of oxalyl, adipoyl, suberoyl and polymethylene moieties. (C) 1996 John Wiley & Sons, Inc.