CONFORMATION CONTROL OF MODEL PEPTIDES BY METAL-IONS - A NEW-TYPE OF TURN STRUCTURE POUND IN [(BOC-CYS-PRO-LEU-CYS-GLY-ALA)HG]

The structure of [(Boc-Cys(1)-Pro-Leu-Cys(4)-Gly-Ala-OMe)Hg], 1, in DM F(-d(7)) and DMSO(-d(6)) solutions was studied by X-ray absorption fin e structure (XAFS), rotating frame nuclear Overhauser effect spectrosc opy (ROESY), distance geometry (DG), molecular dynamics (MD), and rest rained molecular dynamics (RMD). The XAFS study clarified that the ino rganic center of compound 1 adopts a linear coordination with r(HG-S) = 2.33 Angstrom. The NMR experiment revealed 33 atom approximate dista nces for the H-1-H-1 pairs of the main chain loop, including the side chains of the cysteinyl residues (ROESY). By a complementary use of DG , plain MD, and RMD for distance information from NMR as well as XAFS, we established that compound 1 adopts a new type of hybridized turn s tructure. The compound has two hydrogen bonds, Cys(1) S-Leu H-N and Pr o CO-Cys(4) H-N, among which the former is common to the core sites in proteins, Cys(i)-X-Y-Cys(i+3)/M(2+) (Zn2+, Fe2+), whereas the latter is common to the mirror image of the gamma turn structure in proteins.