Probing the role of the C-H···O hydrogen bond stabilized polypeptide chain reversal at the c-terminus of designed peptide helices. Structural characterization of three decapeptides

Aravinda, Subrayashastry ; Shamala, Narayanaswamy ; Bandyopadhyay, Abhishek ; Balaram, Padmanabhan (2003) Probing the role of the C-H···O hydrogen bond stabilized polypeptide chain reversal at the c-terminus of designed peptide helices. Structural characterization of three decapeptides Journal of the American Chemical Society, 125 (49). pp. 15065-15075. ISSN 0002-7863

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Official URL: http://pubs.acs.org/doi/abs/10.1021/ja0372762

Related URL: http://dx.doi.org/10.1021/ja0372762

Abstract

The structural characterization in crystals of three designed decapeptides containing a double d-segment at the C-terminus is described. The crystal structures of the peptides Boc-Leu-Aib-Val-Xxx-Leu-Aib-Val-DAla-DLeu-Aib-OMe, (Xxx = Gly 2, DAla 3, Aib 4) have been determined and compared with those reported earlier for peptide 1 (Xxx = Ala) and the all l analogue Boc-Leu-Aib-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-OMe, which yielded a perfect right-handed α-helical structure. Peptides 1 and 2 reveal a right-handed helical segment spanning residues 1 to 7, ending in a Schellman motif with DAla(8) functioning as the terminating residue. Polypeptide chain reversal occurs at residue 9, a novel feature that appears to be the consequence of a C-H···O hydrogen bond between residue 4 CαH and residue 9 CO groups. The structures of peptides 3 and 4, which lack the pro R hydrogen at the Cα atom of residue 4, are dramatically different. Peptide 3 adopts a right-handed helical conformation over the 1 to 7 segment. Residues 8 and 9 adopt αL conformations forming a C-terminus type I′ β-turn, corresponding to an incipient left-handed twist of the polypeptide chain. In peptide 4, helix termination occurs at Aib(6), with residues 6 to 9 forming a left-handed helix, resulting in a structure that accommodates direct fusion of two helical segments of opposite twist. Peptides 3 and 4 provide examples of chiral residues occurring in the less favored sense of helical twist; DAla(4) in peptide 3 adopts an αR conformation, while LVal(7) in 4 adopts an αL conformation. The structural comparison of the decapeptides reported here provides evidence for the role of specific C-H···O hydrogen bonds in stabilizing chain reversals at helix termini, which may be relevant in aligning contiguous helical and strand segments in polypeptide structures.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
ID Code:4599
Deposited On:18 Oct 2010 07:24
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