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

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          Abstract

          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 H2 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 H2-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 H2 signal transmission. A mutant deleted for a C-terminal peptide of 55 amino acids in HoxB lost its H2-sensing ability but still catalysed H2 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. H2 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 H2-sensing complex with respect to its regulatory function is discussed.

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          Purification and properties of soluble hydrogenase from Alcaligenes eutrophus H 16

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            The Alcaligenes eutrophus H16 hoxX gene participates in hydrogenase regulation.

            Nucleotide sequence analysis revealed a 1,791-bp open reading frame in the hox gene cluster of the gram-negative chemolithotroph Alcaligenes eutrophus H16. In order to investigate the biological role of this open reading frame, we generated an in-frame deletion allele via a gene replacement strategy. The resulting mutant grew significantly more slowly than the wild type under lithoautotrophic conditions (6.1 versus 4.2 h doubling time). A reduction in the level of the soluble NAD-reducing hydrogenase (60% of the wild-type activity) was shown to be the cause of the slow lithoautotrophic growth. We used plasmid-borne gene fusions to monitor the expression of the operons encoding the soluble and membrane-bound hydrogenases. The expression of both operons was lower in the mutant than in the wild-type strain. These results suggest that the newly identified gene, designated hoxX, encodes a regulatory component which, in conjunction with the transcriptional activator HoxA, controls hydrogenase synthesis.
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              The membrane-bound hydrogenase of Alcaligenes eutrophus. I. Solubilization, purification, and biochemical properties

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                Author and article information

                Journal
                Mol. Microbiol.
                Molecular microbiology
                0950-382X
                0950-382X
                Mar 2004
                : 51
                : 6
                Affiliations
                [1 ] Institut für Biologie/Mikrobiologie, Humboldt-Universität zu Berlin, Chausseestr 117, 10115 Berlin, Germany.
                Article
                3933
                10.1111/j.1365-2958.2003.03933.x
                15009894
                e9036263-b308-432f-bb98-d866889fd7ad
                History

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