Solid state and solution conformations of a helical peptide with a central gly-gly segment

✍ Scribed by Isabella L. Karle; Arindam Banerjee; Surajit Bhattacharjya; P. Balaram

• Publisher: Wiley (John Wiley & Sons)
• Year: 1998
• Tongue: English
• Weight: 819 KB
• Volume: 38
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/(sici)1097-0282(199604)38:4<515::aid-bip7>3.0.co;2-w

✦ Synopsis

The influence of amino acids with contrasting con formational tendencies on the stereochemistry qfoligopeptides has been investigated using an octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aih-Val-OMe, which contains two helix-promoting Aib residues and a central helix-de.vtabilizing Gly-Gly segment. Single crystal x-ray diffraction studies reveal that a Slo-helix is formed up to the penultimate Aib residue, at which point there is a helix reversal in the backbone, reminiscent qf a C-terminal6 + I hydrogen bond. The curious feature in the crystal is the solvation of the possible 6 + I bond by a CH30H molecule, where the OH is inserted between 0 ( 3 ) and N ( 8) and participates in hydrogen bonds with both. The cell parameters are as follows: space group P212121r a = 10.649 ( 4 ) A", b = 15.694(5) A', c = 30.181(8) A, R = 6.7% for 3427 data (IFoI > 3aF) observedto 0.9A". Nuclear magnetic resonance studies in CDC13 using NHgroup solvent accessibility and nuclear Overhauser effects as probes are consistent with a 310-helical conformation. In contrast, in (CD3)2S0, unfolding of the central segment results in a multiple P-turn structure, with @-turn conformations populated at residues [1][2][3][4][6][7]2, mixtures also provide evidence for a solvent-dependent structural transition. Helical conformations are populated in TFE, while type II @-turn structures are favored in methanol.