Interaction of Ni(II) and Cu(II) with a metal binding sequence of histone H4: AKRHRK, a model of the H4 tail

摘要

Chromatin proteins are believed to represent reactive sites for nickel binding. The unique structure of the N-terminal tail of histone H4 contains sites for post-translational modification close to a histidine residue capable of anchoring binding sites for metal ions. We have analyzed as a minimal model for the H4 tail, the blocked peptide CH_3CO-AKRHRK-CONH_2 for nickel and copper binding. Ultraviolet-visible, circular dichroism, electron paramagnetic resonance and nuclear magnetic resonance spectroscopic analysis showed that histidine acts as an anchoring metal binding site. A 1N complex is formed between pH = 5-7 and 4-6 for Ni(II) and Cu(II), respectively, while at a higher pH a series of 4N complexes are formed. Above pH 8, the 2N high-spin octahedral resulted in a 4N low-spin planar Ni(II) complex. The stability constants of the Cu(II) (3N, 4N) and Ni(II) (4N) complexes with the peptide model of the H4 were distinctly higher than those for similar blocked peptide with a histidine in the fourth position. Significant shifts in the αproton region in the ~1H NMR spectrum of the 4N Ni-complex showed that the conformation of the peptide had been dramatically affected following Ni(II) complexation.