SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION, AND METAL-ION INTERACTION OF A NEW ALPHA-HELICAL PEPTIDE

A 15-mer model peptide was synthesised by the solid phase method. The solution structure of this peptide was investigated by circular dichro ism (CD) and NMR spectroscopy. CD results indicated that the peptide a dopts a helical conformation in the presence of 2,2,2-trifluoroethanol (TFE) and its helicity is influenced by pH. NMR studies, carried out in H2O/TFE (1:1), allowed the sequence-specific assignment of the prot on resonances to be made, in addition to a more precise location of th e helical structure in the peptide sequence. The ability of different divalent metal ions (Cu2+, Ni2+) to induce an alpha-helix was also inv estigated in aqueous solution by means of CD spectroscopy; the results obtained indicate that Ni2+ is able to promote the a-helical conforma tion at neutral pH. In contrast, the CD spectrum of the Cu2+-peptide c omplex does not show any indication of a helical conformation. The rea sons for this behaviour are proposed on the basis of ESR and UV/Vis da ta.