An NMR Study on Nickel Binding to Cap43 Protein

Cap43 has been reported to be specifically induced by nickel compounds in a variety of cell lines. Its function is not yet clear, but Cap43 protein does appear to be inducec in response to an increase in intracellular concentration of Ca2+, caused by nickel ion exposure in cultured human cells. Cap43 is expressed at low levels in normal tissues. However, in a variety of cancers, it is overexpressed in cancer cells. The peculiarity of Cap43 is its mono-histidinic motif consisting of ten amino acids (TRSRHTSEG) repeated three times in the C-terminus. We have analyzed, for Ni(II) binding, the 30-amino acid C-terminal sequence of the protein, TRSRSHTSEG-TRSRTHTSEG-TRSRSHTSEG, by the use of different NMR techniques such as 1D, NOESY, TOCSY and ROESY experiments. From the data thus collected we calculated a model of the structure for the peptide-Ni(II) complex, confirming the characteristic binding of a nickel ion to each 10-amino acid fragment and showing the interesting structural changes the peptide undergoes upon metal coordination.