title: Crystal structure and solution conformation of S,S'-bis(Boc-Cys-Ala-OMe): intramolecular antiparallel beta-sheet conformation of an acyclic cystine peptide.
abstract: 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 1H- and 13C-nmr, ir, and CD methods. The peptide molecule has a twofold rotation symmetry and adopts an intramolecular antiparallel beta-sheet structure in the solid state. The two antiparallel extended strands are stabilized by two hydrogen bonds between the Boc CO and Ala NH groups [N...O 2.964 (3) A, O...HN 2.11 (3) A, and NH...O angle 162 (3) degrees]. The disulfide bridge has a right-handed conformation with the torsion angle C beta SSC beta = 95.8 (2) degrees. In solution the presence of a twofold rotation symmetry in the molecule is evident from the 1H- and 13C-nmr spectra. 1H-nmr studies, using solvent and temperature dependencies of NH chemical shifts, paramagnetic radical induced line broadening, and rate of deuterium-hydrogen exchange effects on NH resonances, suggest that Ala NH is solvent shielded and intramolecularly hydrogen bonded in CDCl3 and in (CD3)2SO. Nuclear Overhauser effects observed between Cys C alpha H and Ala NH protons and ir studies provide evidence of the occurrence of antiparallel beta-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 beta-sheet structures.
authors.affiliation: Department of Oral Biology, School of Dental Medicine, State University of New York, Buffalo 14214.
authors.forename: P A
authors.initials: PA
authors.lastname: Raj
authors.forename: S D
authors.initials: SD
authors.lastname: Soni
authors.forename: N
authors.initials: N
authors.lastname: Ramasubbu
authors.forename: K K
authors.initials: KK
authors.lastname: Bhandary
authors.forename: M J
authors.initials: MJ
authors.lastname: Levine
mesh_terms: D003553:Cystine / Q000737:chemistry; D004151:Dipeptides / Q000737:chemistry*; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D012996:Solutions
chemical_list: D004151:Dipeptides; D010455:Peptides; D012996:Solutions; C066313:S,S'-bis(tert-butyloxycarbonyl-cysteinylalanine methyl ester); D003553:Cystine