Bacterial genes involved in incorporation of nickel into a hydrogenase enzyme.

Abstract

Nickel is an essential component of all H2-uptake hydrogenases. A (7) but also affects hydrogenase synthesis in wild-type strains of the bacterium (8). From use of inhibitors of 63Ni uptake in B. japonicum JH, it has been suggested that the bulk of nickel is transported via a magnesium transport system (9). A nickel metabolism locus has been identified within the hydrogenase gene cluster of B. japonicum (10). A mutation within this locus resulted in strains that require higher levels of nickel than the wild type for hydrogenase activity, and that produce an (apo)hydrogenase deficient in nickel content (10,11). The mutant strain is not deficient in nickel transport (10). In this study, we have isolated a fragment of DNA which complements the nickelmetabolism locus-deleted mutant strain. Here we report the cloning, sequence,t and characterization of the role of these nickel-metabolism genes from B. japonicum. Complementation and mutant analyses indicate that each ofthe three genes (hupNOP) is needed for complete nickel incorporation into the hydrogenase enzyme. hupO and hupP lack homology to known genes. Of particular comparison interest is the product of hupN, which has a predicted 56% identity to the previously described HoxN (high-affinity nickel-specific transport protein) of A. eutrophus (3). MATERIALS AND METHODS

Membrane Topology of the NixA Nickel Transporter of Helicobacter pylori : Two Nickel Transport-Specific Motifs within Transmembrane Helices II and III

“…63 Ni 2ϩ uptake and urease activity (39) and the reduction of Ni 2ϩ uptake and urease activity seen in isogenic nixA mutants (3). NixA is representative of a small family of high-affinity Ni 2ϩ transporters (4,10,12,19,27,29,30,39,50) which have not been extensively studied and whose structures and functions are not well understood.…”

“…Alignment of the 331-amino-acid NixA sequence with three homologous single-component Ni 2ϩ transporters, HoxN of Alcaligenes eutrophus (50), HupN of Bradyrhizobium japonicum (19), and UreH of thermophilic Bacillus sp. strain TB-90 (30), as well as hydropathy and charge dispersion (49), suggested a preliminary model in which NixA is an integral cytoplasmic membrane protein composed of seven transmembrane domains with the amino terminus located in the periplasm (39).…”

Metal Transport in the Rhizobium-Legume Symbiosis

“…NiCoTs expression in E. coli identifi ed ion preferences ranging from strict selectivity for nickel to a strong preference for cobalt through unbiased transport of both ions (Eitinger et al 2005). B. japonicum HupN was the fi rst member identifi ed in rhizobia (Fu et al 1994). The corresponding gene is located adjacent to a DNA region encoding the nickel-containing enzyme hydrogenase.…”

“…The corresponding gene is located adjacent to a DNA region encoding the nickel-containing enzyme hydrogenase. Analysis of mutants affected in this gene revealed a signifi cant Ni-dependent decrease in hydrogenase activity in free-living cells (Fu et al 1994 . Genes encoding members of this group of transporters in other bacteria are sometimes preceded by sequences for cobalamin riboswitch RNA regulatory elements, suggesting that they might transport this cobalt compound rather than nickel (Schauer et al 2008).…”

Genes Encoding Specific Nickel Transport Systems Flank the Chromosomal Urease Locus of Pathogenic Yersiniae

“…HoxN is an integral protein containing eight membrane-spanning segments (13). Members of this family have been identified in a number of bacteria, including Helicobacter pylori (22), Bradyrhizobium japonicum (14), and Mycobacterium tuberculosis (6), as well as in the fission yeast, Schizosaccharomyces pombe (11). Mutations in either specific transport system lead to a dramatic reduction in bacterial nickel uptake and, consequently, to decreased activity of the relevant nickel-requiring urease and hydrogenase enzymes (12,17,24).…”