Conformation Control of Model Peptides by Metal Ions. A New Type of Turn Structure Found in [(Boc–Cys–Pro–Leu–Cys–Gly–Ala)Hg

Abstract

Abstract The structure of [(Boc–Cys1–Pro–Leu–Cys4–Gly–Ala–OMe)Hg], 1, in DMF(-d7) and DMSO(-d6) solutions was studied by X-ray absorption fine structure (XAFS), rotating frame nuclear Overhauser effect spectroscopy (ROESY), distance geometry (DG), molecular dynamics (MD), and restrained molecular dynamics (RMD). The XAFS study clarified that the inorganic center of compound 1 adopts a linear coordination with r(HG–S) = 2.33 Å. The NMR experiment revealed 33 atom approximate distances for the 1H-1H 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 structure. The compound has two hydrogen bonds, Cys1 S-Leu HN and Pro CO-Cys4 HN, among which the former is common to the core sites in proteins, Cysi–X–Y–Cysi+3/M2+ (Zn2+, Fe2+), whereas the latter is common to the mirror image of the γ turn structure in proteins.