title: Dual roles of Bradyrhizobium japonicum nickelin protein in nickel storage and GTP-dependent Ni mobilization.
abstract: The hydrogenase accessory protein HypB, or nickelin, has two functions in the N(2)-fixing, H(2)-oxidizing bacterium Bradyrhizobium japonicum. One function of HypB involves the mobilization of nickel into hydrogenase. HypB also carries out a nickel storage/sequestering function in B. japonicum, binding nine nickel ions per monomer. Here we report that the two roles (nickel mobilization and storage) of HypB can be separated in vitro and in vivo using molecular and biochemical approaches. The role of HypB in hydrogenase maturation is completely dependent on its intrinsic GTPase activity; strains which produce a HypB protein that is severely deficient in GTPase activity but that fully retains nickel-sequestering ability cannot produce active hydrogenase even upon prolonged nickel supplementation. A HypB protein that lacks the nickel-binding polyhistidine region near the N terminus lacks only the nickel storage capacity function; it is still able to bind a single nickel ion and also retains complete GTPase activity.
authors.affiliation: Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Olson
authors.forename: R J
authors.initials: RJ
authors.lastname: Maier
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D020369:Bradyrhizobium / Q000201:enzymology* / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D005816:Genetic Complementation Test; D006160:Guanosine Triphosphate / Q000378:metabolism; D006864:Hydrogenase / Q000378:metabolism; D015151:Immunoblotting; D008969:Molecular Sequence Data; D009154:Mutation; D009532:Nickel / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C089637:HypB protein, bacteria; D009532:Nickel; D006160:Guanosine Triphosphate; D006864:Hydrogenase; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins