Characterization of beta-turn and Asx-turns mimicry in a model peptide: stabilization via C--H . . . O interaction.

Thakur, A K and Kishore, Raghuvansh (2006) Characterization of beta-turn and Asx-turns mimicry in a model peptide: stabilization via C--H . . . O interaction. Biopolymers, 81 (6). pp. 440-9. ISSN 0006-3525

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The chemical synthesis and single-crystal X-ray diffraction analysis of a model peptide, Boc-Thr-Thr-NH2 (1) comprised of proteinogenic residues bearing an amphiphilic Cbeta -stereogenic center, has been described. Interestingly, the analysis of its molecular structure revealed the existence of a distinct conformation that mimics a typical beta-turn and Asx-turns, i.e., the two Thr residues occupy the left- and right-corner positions. The main-chain torsion angles of the N- and C-terminal residues i.e., semiextended: phi = -68.9 degrees , psi = 128.6 degrees ; semifolded: phi = -138.1 degrees , psi = 2.5 degrees conformations, respectively, in conjunction with a gauche- disposition of the obligatory C-terminus Thr CgammaH3 group, characterize the occurrence of the newly described beta-turn- and Asx-turns-like topology. The preferred molecular structure is suggested to be stabilized by an effective nonconventional main-chain to side-chain Ci=O . . . H--Cgamma(i+2)-type intraturn hydrogen bond. Noteworthy, the observed topology of the resulting 10-membered hydrogen-bonded ring is essentially similar to the one perceived for a classical beta-turn and the Asx-turns, stabilized by a conventional intraturn hydrogen bond. Considering the signs as well as magnitudes of the backbone torsion angles and the orientation of the central peptide bond, the overall mimicked topology resembles the type II beta-turn or type II Asx-turns. An analysis of Xaa-Thr sequences in high-resolution X-ray elucidated protein structures revealed the novel topology prevalence in functional proteins (unpublished). In view of indubitable structural as well as functional importance of nonconventional interactions in bioorganic and biomacromolecules, we intend to highlight the participation of Thr CgammaH in the creation of a short-range C=O . . . H--Cgamma -type interaction in peptides and proteins.

Item Type: Article
Additional Information: Copyright of this article belongs to Wiley.
Uncontrolled Keywords: �-turn; Asx-turns; mimicry; peptide–protein interaction; chemical synthesis; X-ray diffraction INTRODUCTION In recent years, the design and construction of backbone secondary structural mimicry and novel nonrepetitive secondary structural motifs, frequently observed in proteins and peptides, have emerged as important targets diffraction
Subjects: Q Science > QD Chemistry
Depositing User: Dr. K.P.S.Sengar
Date Deposited: 09 Jan 2012 04:24
Last Modified: 08 Jan 2015 09:46

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