Ni(II) and Cu(II) binding with a 14-aminoacid sequence of Cap43 protein, TRSRSHTSEGTRSR

The tetradecapeptide containing the 10 aminoacid repeated sequence on the C -terminus of the Ni(II)-induced Cap43 protein, was analyzed for Ni(II) and Cu(II) binding. A combined pH-metric and spectroscopic UV-VIS, EPR, CD and NMR study of Ni(II) and Cu(II) binding to the blocked CH3CO-Thr-Arg-Ser-Arg -Ser-His-Thr-Ser-Glu-Gly-Thr-Arg-Ser-Arg-NH2 (Ac-TRSRSHTSEGTRSR-Am) peptide , modeling a part of the C-terminal sequence of the Cap43 protein, revealed the formation of octahedral complexes involving imidazole nitrogen of hist idine, at pH 5.5 and pH 7 for Cu(II) and Ni(II), respectively; a major squa re planar 4N-Ni(II) complex (about 100% at pH 9, log K* = -28.16) involving imidazole nitrogen of histidine and three deprotonated amide nitrogens of the backbone of the peptide was revealed; a 3N-Cu(II) complex (maximum abou t 70% at pH 7, log K* = -13.91) and a series of 4N-Cu(II) complexes startin g at pH 5.5 (maximum about 90% at pH 8.7. log K* = -21.39 for CuH-3L), were revealed. This work supports the existence of a metal binding site at the COOH-terminal part of the Cap43 peptide. (C) 2001 Elsevier Science B.V. All rights reserved.