NOVEL DISULFIDE-CONSTRAINED PENTAPEPTIDES AS MODELS FOR BETA-VIA TURNS IN PROTEINS

The conformational behavior of cyclic peptides of the amino acid sequence Cys-Phe/Ala-Pro-Ala-Cys has been investigated through the combined use of molecular simulation methods and MMR experiments to find models for beta-Vla turns of proteins, Both oxidized (cyclic) peptides and reduced (linear) forms were investigated, At least 95% of the cyclic peptides show a cis conformation of the Xaa-Pro bond in solution in DMSO or water, whereas all other peptide bonds are tr ans. Furthermore, we observed a hydrogen bond between the NH group of residue Ala(4) and the C = O group of residue Cys(1). Both properties are indicative of beta-VIa turns, After reduction of the disulfide bridge, the all-trans form of the peptide bonds predominates.