title: Stereochemical constraints in peptide design: analysis of the influence of a disulfide bridge and an alpha-aminoisobutyryl residue on the conformation of a hexapeptide.
abstract: The competing effects of a disulfide bridge and an alpha-aminoisobutyryl residue (Aib) in determining the conformation of a hexapeptide have been investigated, by comparing the cyclic disulfide [sequence: see text] and the acylic peptide Boc-Cys (SBzl)-Val-Aib-Ala-Leu-Cys (SBzl)-NHMe (2). Previously published nmr and crystallographic studies [R. Kishore, S. Raghothama, and P. Balaram (1987) Biopolymers, Vol. 26, pp. 873-891; I. L. Karle, R. Kishore, S. Raghothama, & P. Balaram, (1988) Journal of the American Chemical Society Vol. 110, pp. 1958-1963] have established an antiparallel beta-hairpin structure for 1 with a central Aib-Ala beta-turn. A comparison of nmr data for 1 and 2 in chloroform and dimethylsulfoxide reveals that the acyclic peptide is conformationally labile. Evidence for a 3(10)-helical conformation in CDCl3 is obtained from sensitivity of NH chemical shifts to temperature and solvent perturbation and low JHNC alpha H values. Studies in solvent mixtures establish a conformational transition on going from CDCl3 to (CD3)2SO. The changes in NH nmr parameters, together with the observation of several interresidue C alpha i H-Ni+1H nuclear Overhauser effects support a conformation having a central beta-turn with extended arms in (CD3)2SO. A single Aib residue appears to stabilize a helix in apolar solvents, for the acyclic hexapeptide, while the disulfide bridge serves to lock the beta-hairpin conformation.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore.
authors.forename: K
authors.initials: K
authors.lastname: Uma
authors.forename: R
authors.initials: R
authors.lastname: Kishore
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D000621:Aminoisobutyric Acids / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013237:Stereoisomerism
chemical_list: D000621:Aminoisobutyric Acids; D004220:Disulfides; D009842:Oligopeptides; D010456:Peptides, Cyclic; C100049:2-aminoisobutyric acid