Binding of Nickel(II) and Copper(II) to the N-Terminal Sequence of Human Protamine HP2

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Abstract
A potentiometric and spectroscopic (UV/vis and CD) study of Cu(II) and Ni(II) binding to the N-terminal pentadecapeptide of human protamine HP2 (HP21-15) was performed. The results indicate that the N-terminal tripeptide motif Arg-Thr-His is the exclusive binding site for both metal ions at a metal to HP21-15 molar ratio not higher than 1. The very high value of protonation-corrected stability constant (log *K) for Ni(II)-HP21-15 complex, −19.29, indicates that HP2 has the potential to sequester Ni(II) from other peptide and protein carriers, including albumin. The same is likely for Cu(II) (log *K = −13.13). The CD spectra of Cu(II) and Ni(II) complexes of HP21-15 indicate that the N-terminal metal binding affects the overall conformation of the peptide that, in turn, may alter interaction of HP2 with DNA. These results imply HP2 as a likely target for the toxic metals Ni(II) and Cu(II).

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