Rhizobium leguminosarum HupE is a highly-specific diffusion facilitator for nickel uptake

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Albareda, Marta | Rodrigue, Agnès | Brito, Belén | Ruiz-Argüeso, Tomás | Imperial, Juan | Mandrand-Berthelot, Marie-Andrée | Palacios, Jose

Edité par CCSD ; Royal Society of Chemistry -

International audience. Bacteria require nickel transporters for the synthesis of Ni-containing metalloenzymes in natural, low nickel habitats. In this work we carry out functional and topological characterization of Rhizobium leguminosarum HupE, a nickel permease required for the provision of this element for [NiFe] hydrogenase synthesis. Expression studies in the Escherichia coli nikABCDE mutant strain HYD723 revealed that HupE is a medium-affinity permease (apparent K m 227 AE 21 nM; V max 49 AE 21 pmol Ni 2+ min À1 mg À1 bacterial dry weight) that functions as an energy-independent diffusion facilitator for the uptake of Ni(II) ions. This Ni 2+ transport is not inhibited by similar cations such as Mn 2+ , Zn 2+ , or Co 2+ , but is blocked by Cu 2+. Analysis of site-directed HupE mutants allowed the identification of several residues (H36, D42, H43, F69, E90, H130, and E133) that are essential for HupE-mediated Ni uptake in E. coli cells. By using translational fusions to reporter genes we demonstrated the presence of five transmembrane domains with a periplasmic N-terminal domain and a C-terminal domain buried in the lipid bilayer. The periplasmic N-terminal domain contributes to stability and functionality of the protein.

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