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+.
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