Selective interaction of Hpn-like protein with nickel, zinc and bismuth in vitro and in cells by FRET

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• We constructed fluorescent metal sensor proteins for FRET analysis.
• Ni(II)-, Zn(II)- and Bi(III)-binding to Hpnl selectively was monitored.
• Intracellular binding of Hpnl towards Ni(II) and Zn(II) was shown.
• Interaction between Hpnl and Bi(III) in cells was validated by GE-ICPMS.
• C-terminal Glu-rich motif participated possibly in Bi(III)-binding to Hpnl in vivo.

Hpn-like (Hpnl) is a unique histidine- and glutamine-rich protein found only in Helicobacter pylori and plays a role on nickel homeostasis. We constructed the fluorescent sensor proteins CYHpnl and CYHpnl_1-48 (C-terminal glutamine-rich region truncated) using enhanced cyan and yellow fluorescent proteins (eCFP and eYFP) as the donor–acceptor pair to monitor the interactions of Hpnl with metal ions and to elucidate the role of conserved Glu-rich sequence in Hpnl by fluorescence resonance energy transfer (FRET). CYHpnl and CYHpnl_1-48 exhibited largest responses towards Ni(II) and Zn(II) over other metals studied and the binding of Bi(III) to CYHpnl was observed in the presence of an excess amount of Bi(III) ions (Kd = 115 ± 4.8 μM). Moreover, both CYHpnl and CYHpnl_1-48 showed positive FRET responses towards the binding to Ni(II) and Zn(II) in Escherichia coli cells overexpressing CYHpnl and CYHpnl_1-48, whereas a decrease in FRET upon Bi(III)-binding in E. coli cells overexpressing the latter. Our study provides clear evidence on Hpnl binding to nickel in cells, and intracellular interaction of Hpnl with Bi(III) could disrupt the protein function, thus probably contributing to the efficacy of Bi(III) drugs against H. pylori.

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