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

Abstract

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⁺.