Collateral existence of folded and extended conformations of the beta-Ala moiety in a model peptide.

Kumar Thakur, A and Venugopalan, P and Kishore, Raghuvansh (2000) Collateral existence of folded and extended conformations of the beta-Ala moiety in a model peptide. Biochemical and biophysical research communications, 273 (2). pp. 492-8. ISSN 0006-291X

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Abstract

The single-crystal X-ray diffraction analysis of a nonchiral beta-Ala-containing model peptide, Boc-beta-Ala-Aib-OCH(3) 1 (beta-Ala, 3-aminopropionic acid; Aib, alpha-aminoisobutyric acid), establishes the coexistence of distinctly different backbone conformations in two crystallographically independent molecules, A and B, in the asymmetric unit. Interestingly, the central mu torsion angle around the -C(beta)-C(alpha)- bond of the conformationally flexible beta-Ala residue appears to be critical in dictating the overall distinct structural features, i.e., in molecule A it adopts a folded gauche conformation: mu = -71.0 degrees, whereas it favors an extended trans conformation, mu = 161.2 degrees, in molecule B. As expected, the stereochemically constrained Aib residue preferred an energetically favorable folded backbone conformation, the torsion angles being phi = 46.2 degrees and psi = 48.3 degrees for molecule A and phi = -43.6 degrees and psi = -45.5 degrees for molecule B, lying in the left-handed and right-handed helical regions of the Ramachandran map, respectively. Considering the signs as well as the magnitudes of the backbone torsional angles, molecule A typically folds into a pseudo type III' beta-turn-like structure while molecule B prefers an overall extended conformation. Entrapping the two dramatically distinct conformational characteristics in the crystalline state clearly suggests that the gauche and the trans effects of the beta-Ala moieties are indeed energetically accessible to a short linear peptide and receive strong experimental support. The analyses permitted us to emphasize that in addition to conformational constraints of the neighboring residue, the chemical nature of the side-chain acyclic substituents and the "local environments" collectively seem to influence the stabilization of the folding-unfolding behavior of the two methylene units (-CONH-CH(2)-CH(2)-CONH-) in 1.

Item Type: Article
Additional Information: Copyright of this article belongs to Elsevier Science.
Uncontrolled Keywords: β-Ala peptide; peptide design; X-ray diffraction analysis; folded–unfolded β-Ala moities
Subjects: Q Science > QD Chemistry
Depositing User: Dr. K.P.S.Sengar
Date Deposited: 04 Jan 2012 15:01
Last Modified: 08 Jan 2015 09:50
URI: http://crdd.osdd.net/open/id/eprint/315

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