The H2-sensing complex of Ralstonia eutropha: interaction between a regulatory [NiFe] hydrogenase and a histidine protein kinase.

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摘要：

Two [NiFe] hydrogenases enable the proteobacterium Ralstonia eutropha H16 to grow on molecular hydrogen as the sole energy source. A third [NiFe] hydrogenase (RH) acts as an H 2 sensor in a multiple component signal transduction chain that controls hydrogenase gene transcription. The RH forms a dimeric heterodimer (HoxBC) 2 in which HoxC contains the H 2 -sensing active site and HoxB the electron-transferring components including an organic, not yet identified redox cofactor. This oligomer forms a tight complex with the histidine protein kinase HoxJ. Both the sensor and the kinase were analysed by mutagenesis for functional domains that are instrumental in H 2 signal transmission. A mutant deleted for a C-terminal peptide of 55 amino acids in HoxB lost its H 2 -sensing ability but still catalysed H 2 oxidation. The mutant protein failed to form the dimeric heterodimer and a complex with HoxJ. The organic redox cofactor was no longer detectable in the truncated sensor. H 2 sensing was also abolished by deletion of the PAS domain of HoxJ, indicating that this domain is involved in signal transduction. A truncated version of HoxJ consisting of only the input domain of the kinase was still capable of forming a complex with the RH. Mass determination of the purified HoxJ protein revealed that the kinase forms a homotetramer. The unique oligomeric structure of the H 2 -sensing complex with respect to its regulatory function is discussed.

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关键词：

Hydrogen Nickel Hydrogenase Protein Kinases Bacterial Proteins Signal Transduction Transcription, Genetic Gene Expression Regulation, Bacterial Dimerization Plasmids