H elicobacter pylori periplasmic receptor CeuE ( HP 1561) modulates its nickel affinity via organic metallophores

Summary In G ram‐negative bacteria, nickel uptake is guaranteed by multiple and complex systems that operate at the membrane and periplasmic level. H elicobacter pylori employs other yet uncharacterized systems to import the nickel required for the maturation of key enzymes, such as urease and hydrogenase. H . pylori CeuE protein ( HP 1561), previously annotated as the periplasmic component of an ATP ‐binding cassette ( ABC )‐type transporter apparatus responsible of haem/siderophores or other F e( III )‐complexes uptake, has been recently proposed to be on the contrary involved in nickel/cobalt acquisition. In this work, the crystal structure of H . pylori CeuE has been determined at 1.65 Å resolution using the single anomalous dispersion ( SAD ) method. It comprises two structurally similar globular domains, each consisting of a central five‐stranded β‐sheet surrounded by α‐helices, an arrangement commonly classified as a R ossmann‐like fold. Structurally, H . pylori CeuE belongs to the class III periplasmic substrate‐binding protein. Both crystallographic data and fluorescence binding assays allow to exclude a role of the protein in the transport of V itamin B 12, enterobactin, haem and isolated Ni 2+ ions. On the contrary, the crystal structure and plasmon resonance studies about CeuE / N i‐( l ‐ His ) 2 complex indicate that in H . pylori nickel transport is supported by CeuE protein and requires the presence of a natural nickelophore, analogously to what has been recently demonstrated for NikA from E scherichia coli .