Periplasmic HupE region-Ni2+ interactions: Thermodynamics, binding mode and competition with Cu2+ and Zn2+

The periplasmic fragment of HupE, a nickel transporter, forms complexes with Ni2+, Cu2+ and Zn2+, in which at physiological pH, the coordination sphere consists of the imidazole and amine nitrogens of His1 and the imidazole of His5. Cu2+ is able to displace Ni2+ from its binding site, while Zn2+ cannot.75