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Effects of Hydrogen-Bond Deletion on Peptide Helices: Structural Characterization of Depsipeptides Containing Lactic Acid

Karle, Isabella L and Das, Chittaranjan and Balaram, P (2001) Effects of Hydrogen-Bond Deletion on Peptide Helices: Structural Characterization of Depsipeptides Containing Lactic Acid. In: Biopolymers, 59 (4). pp. 276-289.

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Abstract

The insertion of alpha-hydroxy acids into peptide chains provides a convenient means for investigating the effects of hydrogen bond deletion on polypeptide secondary structures. The crystal structures of three oligopeptides containing L-lactic acid (Lac) residue have been determined. Peptide 1, Boc-Val-Ala-Leu-Aib - Val-Lac-Leu-Aib-Val-Ala-Leu-OMe (Boc: tert-butyloxycarbonyl; Aib: alpha- aminoisobutyric acid; OMe: methyl ester), and peptide 2, Boc-Val-Ala-Leu-Aib - Val-Lac-Leu-Aib-Val-Leu-OMe, adopt completely helical conformations in the crystalline state with the Lac(6) residue comfortably accommodated in the center of a helix. The distance between the O atoms of Leu(3) CO group and the Lac(6) O (ester) in both the structures is 3.1-3.3 Å. The NMR and CD studies of peptide 1 and its all-amide analogue 4, Boc-Val-Ala-Leu-Aib - Val-Ala-Leu-Aib-Val-Ala-Leu-OMe, provide firm evidence for a continuous helical conformation in solution in both the cases. In a 14-residue peptide 3, Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-Val-Ala-Leu-Aib-Val-Lac-Leu-OMe, residues Val(1)-Leu(10) adopt a helical conformation. Aib(11) is the site of chiral reversal resulting in helix termination by formation of a Schellman motif. Residues 12-14 adopt nonhelical conformations. The loss of the hydrogen bond near the C-terminus appears to facilitate the chiral reversal at Aib(11).

Item Type: Journal Article
Additional Information: Copyright for this article belongs to John Wiley & Sons, Inc
Keywords: 14-residue peptides;Helix reversal;Helix termination;Lac contained in helical backbone;X-ray crystal structures
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 24 Aug 2004
Last Modified: 19 Sep 2010 04:14
URI: http://eprints.iisc.ernet.in/id/eprint/1319

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