title: Cyanobacterial-type, heteropentameric, NAD+-reducing NiFe hydrogenase in the purple sulfur photosynthetic bacterium Thiocapsa roseopersicina.
abstract: Structural genes coding for two membrane-associated NiFe hydrogenases in the phototrophic purple sulfur bacterium Thiocapsa roseopersicina (hupSL and hynSL) have recently been isolated and characterized. Deletion of both hydrogenase structural genes did not eliminate hydrogenase activity in the cells, and considerable hydrogenase activity was detected in the soluble fraction. The enzyme responsible for this activity was partially purified, and the gene cluster coding for a cytoplasmic, NAD+-reducing NiFe hydrogenase was identified and sequenced. The deduced gene products exhibited the highest similarity to the corresponding subunits of the cyanobacterial bidirectional soluble hydrogenases (HoxEFUYH). The five genes were localized on a single transcript according to reverse transcription-PCR experiments. A sigma54-type promoter preceded the gene cluster, suggesting that there was inducible expression of the operon. The Hox hydrogenase was proven to function as a truly bidirectional hydrogenase; it produced H2 under nitrogenase-repressed conditions, and it recycled the hydrogen produced by the nitrogenase in cells fixing N2. In-frame deletion of the hoxE gene eliminated hydrogen evolution derived from the Hox enzyme in vivo, although it had no effect on the hydrogenase activity in vitro. This suggests that HoxE has a hydrogenase-related role; it likely participates in the electron transfer processes. This is the first example of the presence of a cyanobacterial-type, NAD+-reducing hydrogenase in a phototrophic bacterium that is not a cyanobacterium. The potential physiological implications are discussed.
authors.affiliation: Institute of Biophysics, Biological Research Center, Hungarian Academy of Sciences, University of Szeged, H-6726 Szeged, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Rákhely
authors.forename: Akos T
authors.initials: AT
authors.lastname: Kovács
authors.forename: Gergely
authors.initials: G
authors.lastname: Maróti
authors.forename: Barna D
authors.initials: BD
authors.lastname: Fodor
authors.forename: Gyula
authors.initials: G
authors.lastname: Csanádi
authors.forename: Dóra
authors.initials: D
authors.lastname: Latinovics
authors.forename: Kornél L
authors.initials: KL
authors.lastname: Kovács
mesh_terms: D001483:Base Sequence; D017353:Gene Deletion; D005798:Genes, Bacterial; D006859:Hydrogen / Q000378:metabolism; D006864:Hydrogenase / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D010788:Photosynthesis; D012995:Solubility; D020616:Thiocapsa roseopersicina / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
chemical_list: D009243:NAD; D006859:Hydrogen; C043296:nickel-iron hydrogenase; D006864:Hydrogenase