The -Cys-Cys- motif in Helicobacter pylori's Hpn and HspA proteins is an essential anchoring site for metal ions

The Hpn and HspA proteins from H. pylori are significant for nickel homeostasis and protect the cells from higher concentrations of external metal ions. Both proteins have a unique histidine-and cysteine-rich domain at the C terminus. The interactions of Ni2+, Bi3+, Zn2+ and Cd2+ ions with C-terminal Ac-CCSTSDSHHQ-NH2 and Ac-EEGCCHGHHE-NH2 fragments from Hpn and the Ac-GSCCHTGNHD-NH2 sequence from HspA were studied by potentiometry, mass spectrometry, circular dichroism and UV-Vis spectroscopy. Ac-CC-NH2 was used as a reference peptide. The studies have shown that nickel ions form planar complexes with a {2S(-), N-} binding mode. The thiol sulfurs of the -Cys-Cys- motif are also the anchoring sites for Bi3+, Zn2+ and Cd2+ ions. The studied protein fragments have the highest affinity for Bi3+ ions. The thermodynamic stability of Ni2+ is much higher then that of Zn2+.