Conformational analysis of small disulfide loops. Spectroscopic and theoretical studies on a synthetic cyclic tetrapeptide containing cystine
- 1 October 1982
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 21 (22) , 5502-5509
- https://doi.org/10.1021/bi00265a019
Abstract
The conformational analysis of the synthetic peptide .**GRAPHIC**. [Boc = butyloxycarbonyl] was carried out, as a model for small disulfide loops, in biologically active polypeptides. 1H NMR studies (270 MHz) establish that the Val(3) and Cys(4) NH groups are solvent shielded, while 13C studies establish an all-trans peptide backbone. Circular dichroism and Raman spectroscopy provide evidence for a right-handed twist of the s.s. bond. Analysis of the vicinal (J.alpha..beta.) coupling constants for the 2 Cys residues establishes that .chi.1 .apprx. .+-. 60.degree. for Cys(4), while some flexibility is suggested at Cys(1). Conformational energy calculations, imposing intramolecular H-bonding constraints, favor a .beta.-turn (type I) structure with Pro(2)-Val(3) as the corner residues. Theoretical and spectroscopic results are consistent with the presence of a transannular 4 .fwdarw. 1 H-bond between Cys(1) CO and Cys(4) NH groups, with the Val NH being sterically shielded from the solvent environment.This publication has 19 references indexed in Scilit:
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