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Expanding the Peptide beta-Turn in alpha gamma Hybrid Sequences: 12 Atom Hydrogen Bonded Helical and Hairpin Turns

Chatterjee, Sunanda and Vasudev, Prema G and Raghothama, Srinivasarao and Ramakrishnan, Chandrasekharan and Shamala, Narayanaswamy and Balaram, Padmanabhan (2009) Expanding the Peptide beta-Turn in alpha gamma Hybrid Sequences: 12 Atom Hydrogen Bonded Helical and Hairpin Turns. In: Journal of the American Chemical Society, 131 (16). pp. 5956-5965.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/ja900618h

Abstract

Hybrid peptide segments containing contiguous alpha and gamma amino acid residues can form C-12 hydrogen bonded turns which may be considered as backbone expanded analogues of C-10 beta-turns) found in alpha alpha segments. Exploration of the regular hydrogen bonded conformations accessible for hybrid alpha gamma sequences is facilitated by the use of a stereochemically constrained gamma amino acid residue gabapentin (1-aminomethylcyclohexaneacetic acid, Gpn), in which the two torsion angles about C-gamma-C-beta (theta(1)) and C-beta-C-alpha (theta(2)) are predominantly restricted to gauche conformations. The crystal structures of the octapeptides Boc-Gpn-Aib-Gpn-Aib-Gpn-Aib-Gpn-Aib-OMe (1) and Boc-Leu-Phe-Val-Aib-Gpn-Leu-Phe-Val-OMe (2) reveal two distinct conformations for the Aib-Gpn segment. Peptide 1 forms a continuous helix over the Aib(2)-Aib(6) segment, while the peptide 2 forms beta-hairpin structure stabilized by four cross-strand hydrogen bonds with the Aib-Gpn segment forming a nonhelical C-12 turn. The robustness of the helix in peptide 1 in solution is demonstrated by NMR methods. Peptide 2 is conformationally fragile in solution with evidence of beta-hairpin conformations being obtained in methanol. Theoretical calculations permit delineation of the various C-12 hydrogen bonded structures which are energetically feasible in alpha gamma and gamma alpha sequences.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Division of Chemical Sciences > NMR Research Centre (Formerly SIF)
Division of Physical & Mathematical Sciences > Physics
Date Deposited: 08 Mar 2010 10:14
Last Modified: 19 Sep 2010 05:56
URI: http://eprints.iisc.ernet.in/id/eprint/26018

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