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Cystine peptides: The intramolecular antiparallel β‐sheet conformation of a 20‐membered cyclic peptide disulfide
Author(s) -
Kishore R.,
Raghothama S.,
Balaram P.
Publication year - 1987
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360260608
Subject(s) - antiparallel (mathematics) , chemistry , intramolecular force , hydrogen bond , peptide , cyclic peptide , disulfide bond , beta sheet , stereochemistry , crystallography , cystine , molecule , cysteine , organic chemistry , biochemistry , enzyme , physics , quantum mechanics , magnetic field
A 20‐membered cyclic peptide disulfidehas been synthesized as a conformational model for disulfide loops of limited ring size. 1 H‐nmr studies at 270 MHz establish the presence of three intramolecular hydrogen bonds involving the Leu, Val, and methylamide NH groups in CDCl 3 . Evidence for peptide aggregation in CDCl 3 is also presented. A structural transition involving loosening of the hydrogen bond formed by the Val NH group is observed upon the measured addition of (CD 3 ) 2 SO to CDCl 3 . Hydrogen‐bonding studies, together with unusually low field positions of the Cys(1) and Cys(6) C α H resonances and high J HNC α Hvalues provide support for an intramolecular antiparallel β‐sheet conformation, facilitated by a chain reversal at the Aib‐Ala segment. Extensive nuclear Overhauser effect studies provide compelling evidence for the proposed conformation and also establish a type I′ β‐turn at the Aib‐Ala residues, the site of the chain reversal.