Potentiometric and spectroscopic studies on the copper(ii) complexes of rat amylin fragments. The anchoring ability of specific non-coordinating side chains

Copper( ii ) complexes of peptides modelling the sequence of the 17-22 residues of rat amylin have been studied by potentiometric, UV-Vis, CD and ESR spectroscopic methods. The peptides were synthesized in N-terminally free forms, NH 2 -VRSSNN-NH 2 , NH 2 -VRSSAA-NH 2 , NH 2 -VRAANN-NH 2 , NH 2 -VRSS-NH 2 , NH 2 -SSNN-NH 2 , NH 2 -SSNA-NH 2 and NH 2 -AANN-NH 2 , providing a possibility for the comparison of the metal binding abilities of the amino terminus and the -SSNN- domain. The amino terminus was the primary ligating site in all cases and the formation of only mononuclear complexes was obtained for the tetrapeptides. The thermodynamic stability of the (NH 2 , N − , N − ) coordinated complexes was, however, enhanced by the asparaginyl moiety in the case of NH 2 -SSNN-NH 2 , NH 2 -SSNA-NH 2 and NH 2 -AANN-NH 2 . Among the hexapeptides the formation of dinuclear complexes was characteristic for NH 2 -VRSSNN-NH 2 demonstrating the anchoring ability of the -SSNN- (SerSerAsnAsn) domain. The complexes of the heptapeptide NH 2 -GGHSSNN-NH 2 were also studied and the data supported the above mentioned anchoring ability of the -SSNN- site. The studies of rat amylin fragments and their mutants demonstrate the anchoring ability of -SerSerAsnAsn- domain.