Characterization of transcriptional regulation of Shewanella frigidimarina Fe(III)-induced flavocytochrome c reveals a novel iron-responsive gene regulation system.

The bacterium Shewanella frigidimarina can grow anaerobically by utilizing Fe(III) as a respiratory electron acceptor. This results in the synthesis of a number of periplasmic c-type cytochromes, which are absent when the organism is grown in the absence of added Fe(III). One cytochrome, IfcA, is synthesized when Fe(III) is present as the sole respiratory electron acceptor or when it is present in combination with oxygen, fumarate, or nitrate. The ifcA gene was thus selected for a study of iron-responsive gene regulation of respiratory proteins in S. frigidimarina. The monocistronic ifcA gene clusters with two other monocistronic genes, ifcO, encoding a putative outer membrane porin, and ifcR, encoding a putative transcriptional regulator of the LysR superfamily. Analysis of transcription of all three genes under a range of growth conditions in the wild type and an ifcR insertion mutant and analysis of a strain that constitutively expresses ifcR revealed that iron regulation is exerted at the level of ifcR transcription. In the presence of Fe(III) IfcR is synthesized and acts positively to regulate expression of ifcO and ifcA. Control of Fe(III) respiration by this novel regulatory system differs markedly from Fur-mediated regulation of iron assimilation, in which Fur serves as an Fe(II)-activated repressor

Structure of hydrogenase maturation protein HypF with reaction intermediates shows two active sites

[NiFe]-hydrogenases are multimeric proteins. The large subunit contains the NiFe(CN) 2CO bimetallic active center and the small subunit contains Fe-S clusters. Biosynthesis and assembly of the NiFe(CN) 2CO active center requires six Hyp accessory proteins. The synthesis of the CN - ligands is catalyzed by the combined actions of HypF and HypE using carbamoylphosphate as a substrate. We report the structure of Escherichia coli HypF(92-750) lacking the N-terminal acylphosphatase domain. HypF(92-750) comprises the novel Zn-finger domain, the nucleotide-binding YrdC-like domain, and the Kae1-like universal domain, also binding a nucleotide and a Zn 2+ ion. The two nucleotide-binding sites are sequestered in an internal cavity, facing each other and separated by 3c14 . The YrdC-like domain converts carbamoyl moiety to a carbamoyl adenylate intermediate, which is channeled to the Kae1-like domain. Mutations within either nucleotide-binding site compromise hydrogenase maturation but do not affect the carbamoylphosphate phosphatase activity. \ua9 2011 Elsevier Ltd All rights reserved.Peer reviewed: YesNRC publication: Ye