Crystal structure and solution conformation of S,S′-bis(Boc-Cys-Ala-OMe): Intramolecular antiparallel β-sheet conformation of an acyclic cystine peptide
✍ Scribed by P. Antony Raj; S. D. Soni; N. Ramasubbu; K. K. Bhandary; M. J. Levine
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1990
- Tongue
- English
- Weight
- 794 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
The conformation of the acyclic biscystine peptide S,S'-bis (Boc-Cys-Ala-OMe) has been studied in the solid state by x-ray diffraction, and in solution by 'H-and "C-nmr, ir, and CD methods. The peptide molecule has a twofold rotation symmetry and adopts an intramolecular antiparallel @-sheet structure in the solid state. The two antiparaliel extended strands are stabilized by two hydrogen bonds between the Boc CO and Aia NH groups [N---O2.964(3)A,O*..HN2.11 (3)A,andNH...0angle162(3)0].Thedisulfide bridge has a right-handed conformation with the torsion angle CdSsSCB = 95.8 ( 2) " . In solution the presence of a twofold rotation symmetry in the molecule is evident from the 'H-and I3C-nmr spectra. 'H-nmr studies, using solvent and temperature dependencies of N H chemical shifts, paramagnetic radical induced line broadening, and rate of deuteriumhydrogen exchange effects on NH resonances, suggest that Ala NH is solvent shielded and intramolecularly hydrogen bonded in CDC13 and in ( CD3 )2S0. Nuclear Overhauser effects observed between Cys C"H and Ala NH protons and ir studies provide evidence of the occurrence of antiparallel B-sheet structure in these solvents. The CD spectra of the peptide in organic solvents are characteristic of those observed for cystine peptides that have been shown to adopt antiparallel @-sheet structures.