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Accommodation of a D-Phe Residue into a Right-Handed 310-Helix: Structure of Boc-D-Phe- ( Aib)4-Gly-L-Leu-(Aib)2-OMe, an Analogue of the Amino Terminal Segment of Antiamoebins and Emerimicins

Karle, IL and Flippen-Anderson, JL and Uma, K and Balaram, P (1993) Accommodation of a D-Phe Residue into a Right-Handed 310-Helix: Structure of Boc-D-Phe- ( Aib)4-Gly-L-Leu-(Aib)2-OMe, an Analogue of the Amino Terminal Segment of Antiamoebins and Emerimicins. In: Biopolymers, 33 (3). pp. 401-407.

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Abstract

The crystal structure of the nonapeptide Boc-D-Phe-Aib-Aib-Aib-Aib-Gly-Leu-Aib-Aib-OMe (I), which is an analogue of the N-terminal sequence of antiamoebins and emerimicins, establishes a completely 310-helical conformation with seven successive intramolecular 4 - 1 hydrogen bonds. The average phi, psi values for residues 1-8 are –59 deg and –32 deg, respectively. Crystal parameters are C47H77N9O12, space group P1, a = 10.636(4) Å, b = 11.239(4) Å, c = 12.227(6) Å, alpha = 101.17(4) deg Å , beta = 97.22(4) deg, gamma = 89.80(3) deg, Z = 1, R = 5.95% for 3018 data with [Fo] > 3a(F), resolution 0.93 Å. The use of the torsion angle k = C ( i - l ) N ( i ) Calpha( i)Cbeta( i) , where k = 68" for D-Phe and k = 164' for L-Leu, confirms the opposite configurations of these residues. The phi, psi values of –62 deg and –32 deg at D-Phe are unusual, since this region is characteristic of residues with L configurations. Peptide I possesses only two chiral residues of opposing configuration. The observed right-handed 310-helical structure suggests that helix sense has probably been determined by the stereochemical preferences of the Leu residue.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to John Wiley & Sons, Inc.
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 07 Dec 2004
Last Modified: 19 Sep 2010 04:17
URI: http://eprints.iisc.ernet.in/id/eprint/2403

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