title: Solid state and solution conformations of a helical peptide with a central Gly-Gly segment.
abstract: The influence of amino acids with contrasting conformational tendencies on the stereochemistry of oligopeptides has been investigated using an octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe, which contains two helix-promoting Aib residues and a central helix-destabilizing Gly-Gly segment. Single crystal x-ray diffraction studies reveal that a 3(10)-helix is formed up to the penultimate Aib residue, at which point there is a helix reversal in the backbone, reminiscent of a C-terminal 6-->1 hydrogen bond. The curious feature in the crystal is the solvation of the possible 6-->1 bond by a CH3OH molecule, where the OH is inserted between O(3) and N(8) and participates in hydrogen bonds with both. The cell parameters are as follows: space group P2(1)2(1)2(1), a = 10.649 (4) A, b = 15.694 (5) A, c = 30.181 (8) A, R = 6.7% for 3427 data (magnitude of F0 > 3 sigma F) observed to 0.9 A. Nuclear magnetic resonance studies in CDCl3 using NH group solvent accessibility and nuclear Overhauser effects as probes are consistent with a 3(10)-helical conformation. In contrast, in (CD3)2SO, unfolding of the central segment results in a multiple beta-turn structure, with beta-turn conformations populated at residues 1-2, 3-4, and 6-7. CD studies in methanol-2,2,2-trifluoroethanol (TFE) mixtures also provide evidence for a solvent-dependent structural transition. Helical conformations are populated in TFE, while type II beta-turn structures are favored in methanol.
authors.affiliation: Laboratory for the Structure of Matter, Naval Research Laboratory, Washington, DC 20375-5000, USA.
authors.forename: I L
authors.initials: IL
authors.lastname: Karle
authors.forename: A
authors.initials: A
authors.lastname: Banerjee
authors.forename: S
authors.initials: S
authors.lastname: Bhattacharjya
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012996:Solutions; D014961:X-Ray Diffraction
chemical_list: D009842:Oligopeptides; D012996:Solutions