Specific binding of Zn2+, Cd2+ and Ni2+ ions by a cyclic four-cysteinyl peptide

Abstract

The metal binding abilities of the GCASCDNCRACKK cyclic peptide towards Zn²⁺, Cd²⁺ and Ni²⁺ ions were studied by potentiometric and spectroscopic methods. The aim of this work was to understand the impact of cyclization on the peptide binding mode and the stability of the formed metal complexes when compared to its linear Ac-GCASCDNCRACKK-NH₂ analogue. The obtained results clearly indicate that in the case of Cd²⁺ and Ni²⁺ complexes, the cyclization of the coordinating peptide distinctly increases the complex stability in the whole pH range studied. Surprisingly, different results were obtained for Zn²⁺ complexes. The peptide cyclization seems to prevent the binding of all four available cysteinyl residues to the Zn²⁺ ion, resulting in the reduced stability of the respective complexes.