Interaction of Cap43 Protein Fragments with Ni(II) and Cu(II)

Cap43 protein has been tested for metal binding domains. The protein, specifically induced by nickel compounds in cultured human cells, had a monohistidinic motif consisting of 10 aminoacids repeated consecutively three times in the C-terminus. We have analyzed, for Ni(II) and Cu(II) binding, the ten Ac-TRSRSH(6) TSEG aminoacid fragment, and successively, the two (Ac-TRSRSH(6) TSEG-TRSRSH(16) TSEG) and the three (Ac-TRSRSH(6) TSEG-TRSRSH(16) TSEG-TRSRSH(26) TSEG) repeated decapeptide fragments. A combined spectroscopic (UV-Vis, EPR) and potentiometric study showed that the coordination starts from the imidazole nitrogen atom of the histidine residue that acts as an anchoring site for both the metal ions. By raising the pH, Ni(H) and Cu(II) ions are able to deprotonate successive nitrogen atoms from the backbone, forming N(-) bonds and planar 4N(N(im), 3N(-)) complexes. Depending on the metal to ligand molar ratio, Ni(2)-20aa, Cu(2)-20aa and Ni(3)-30aa species, where each metal ion is coordinated to the hystidine residue of each ten aminoacid fragment, have been obtained.