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Dual role of HupF in the biosynthesis of [NiFe] hydrogenase in Rhizobium leguminosarum.

ABSTRACT: BACKGROUND: [NiFe] hydrogenases are enzymes that catalyze the oxidation of hydrogen into protons and electrons, to use H? as energy source, or the production of hydrogen through proton reduction, as an escape valve for the excess of reduction equivalents in anaerobic metabolism. Biosynthesis of [NiFe] hydrogenases is a complex process that occurs in the cytoplasm, where a number of auxiliary proteins are required to synthesize and insert the metal cofactors into the enzyme structural units. The endosymbiotic bacterium Rhizobium leguminosarum requires the products of eighteen genes (hupSLCDEFGHIJKhypABFCDEX) to synthesize an active hydrogenase. hupF and hupK genes are found only in hydrogenase clusters from bacteria expressing hydrogenase in the presence of oxygen. RESULTS: HupF is a HypC paralogue with a similar predicted structure, except for the C-terminal domain present only in HupF. Deletion of hupF results in the inability to process the hydrogenase large subunit HupL, and also in reduced stability of this subunit when cells are exposed to high oxygen tensions. A ?hupF mutant was fully complemented for hydrogenase activity by a C-terminal deletion derivative under symbiotic, ultra low-oxygen tensions, but only partial complementation was observed in free living cells under higher oxygen tensions (1% or 3%). Co-purification experiments using StrepTag-labelled HupF derivatives and mass spectrometry analysis indicate the existence of a major complex involving HupL and HupF, and a less abundant HupF-HupK complex. CONCLUSIONS: The results indicate that HupF has a dual role during hydrogenase biosynthesis: it is required for hydrogenase large subunit processing and it also acts as a chaperone to stabilize HupL when hydrogenase is synthesized in the presence of oxygen.

SUBMITTER: Albareda M

PROVIDER: S-EPMC3534401 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Dual role of HupF in the biosynthesis of [NiFe] hydrogenase in Rhizobium leguminosarum.

Albareda Marta M Manyani Hamid H Imperial Juan J Brito Belén B Ruiz-Argüeso Tomás T Böck August A Palacios Jose-Manuel JM

BMC microbiology 20121108

<h4>Background</h4>[NiFe] hydrogenases are enzymes that catalyze the oxidation of hydrogen into protons and electrons, to use H₂ as energy source, or the production of hydrogen through proton reduction, as an escape valve for the excess of reduction equivalents in anaerobic metabolism. Biosynthesis of [NiFe] hydrogenases is a complex process that occurs in the cytoplasm, where a number of auxiliary proteins are required to synthesize and insert the metal cofactors into the enzyme structural unit ...[more]

PMID: 23136881

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Project description:BackgroundA traditional concept in bacterial genetics states that housekeeping genes, those involved in basic metabolic functions needed for maintenance of the cell, are encoded in the chromosome, whereas genes required for dealing with challenging environmental conditions are located in plasmids. Exceptions to this rule have emerged from genomic sequence data of bacteria with multipartite genomes. The genome sequence of R. etli CFN42 predicts the presence of panC and panB genes clustered together on the 642 kb plasmid p42f and a second copy of panB on plasmid p42e. They encode putative pantothenate biosynthesis enzymes (pantoate-β-alanine ligase and 3-methyl-2-oxobutanoate hydroxymethyltransferase, respectively). Due to their ubiquitous distribution and relevance in the central metabolism of the cell, these genes are considered part of the core genome; thus, their occurrence in a plasmid is noteworthy. In this study we investigate the contribution of these genes to pantothenate biosynthesis, examine whether their presence in plasmids is a prevalent characteristic of the Rhizobiales with multipartite genomes, and assess the possibility that the panCB genes may have reached plasmids by horizontal gene transfer.ResultsAnalysis of mutants confirmed that the panC and panB genes located on plasmid p42f are indispensable for the synthesis of pantothenate. A screening of the location of panCB genes among members of the Rhizobiales showed that only R. etli and R. leguminosarum strains carry panCB genes in plasmids. The panCB phylogeny attested a common origin for chromosomal and plasmid-borne panCB sequences, suggesting that the R. etli and R. leguminosarum panCB genes are orthologs rather than xenologs. The panCB genes could not totally restore the ability of a strain cured of plasmid p42f to grow in minimal medium.ConclusionsThis study shows experimental evidence that core panCB genes located in plasmids of R. etli and R. leguminosarum are indispensable for the synthesis of pantothenate. The unusual presence of panCB genes in plasmids of Rhizobiales may be due to an intragenomic transfer from chromosome to plasmid. Plasmid p42f encodes other functions required for growth in minimal medium. Our results support the hypothesis of cooperation among different replicons for basic cellular functions in multipartite rhizobia genomes.

Project description:Rhizobium leguminosarum bv. viciae UPM791 contains a second copy of the fnrN gene, which encodes a redox-sensitive transcriptional activator functionally homologous to Escherichia coli Fnr. This second copy (fnrN2) is located in the symbiotic plasmid, while fnrN1 is in the chromosome. Isolation and sequencing of the fnrN2 gene revealed that the deduced amino acid sequence of FnrN2 is 87.5% identical to the sequence of FnrN1, including a conserved cysteine-rich motif characteristic of Fnr-like proteins. Individual R. leguminosarum fnrN1 and fnrN2 mutants exhibited a Fix+ phenotype and near wild-type levels of nitrogenase and hydrogenase activities in pea (Pisum sativum L.) nodules. In contrast, an fnrN1 fnrN2 double mutant formed ineffective nodules lacking both nitrogenase and hydrogenase activities. Unlike the wild-type strain and single fnrN1 or fnrN2 mutants, the fnrN1 fnrN2 double mutant was unable to induce micro-oxic or bacteroid activation of the hypBFCDEX operon, which encodes proteins essential for hydrogenase synthesis. In the search for symbiotic genes that could be controlled by FnrN, a fixNOQP operon, putatively encoding a micro-oxically induced, bacteroid-specific cbb3-type terminal cytochrome oxidase, was isolated from strain UPM791 and partially sequenced. The fixNOQP operon was present in a single copy located in the symbiotic plasmid, and an anaerobox was identified in the fixN promoter region. Consistent with this, a fixNOQP'-lacZ fusion was shown to be highly induced in micro-oxic cells of the wild-type strain. A high level of micro-oxic induction was also observed in single fnrN1 and fnrN2 mutants, but no detectable induction was observed in the fnrN1 fnrN2 double mutant. The lack of expression of fixNOQP in the fnrN1 fnrN2 double mutant is likely to cause the observed Fix- phenotype. These data demonstrate that, contrary to the situation in other rhizobia, FnrN controls both hydrogenase and nitrogenase activities of R. leguminosarum bv. viciae UPM791 in the nodule and suggest that this strain lacks a functional fixK gene.

Project description:BACKGROUND:Photosynthetic microorganisms that directly channel solar energy to the production of molecular hydrogen are a potential future biofuel system. Building such a system requires installation of a hydrogenase in the photosynthetic organism that is both tolerant to oxygen and capable of hydrogen production. Toward this end, we have identified the [NiFe] hydrogenase from the marine bacterium Alteromonas macleodii "Deep ecotype" that is able to be heterologously expressed in cyanobacteria and has tolerance to partial oxygen. The A. macleodii enzyme shares sequence similarity with the uptake hydrogenases that favor hydrogen uptake activity over hydrogen evolution. To improve hydrogen evolution from the A. macleodii hydrogenase, we examined the three Fe-S clusters found in the small subunit of many [NiFe] uptake hydrogenases that presumably act as a molecular wire to guide electrons to or from the active site of the enzyme. Studies by others altering the medial cluster of a Desulfovibrio fructosovorans hydrogenase from 3Fe-4S to 4Fe-4S resulted in two-fold improved hydrogen evolution activity. RESULTS:We adopted a strategy of screening for improved hydrogenase constructs using an Escherichia coli expression system before testing in slower growing cyanobacteria. From the A. macleodii enzyme, we created a mutation in the gene encoding the hydrogenase small subunit that in other systems is known to convert the 3Fe-4S medial cluster to 4Fe-4S. The medial cluster substitution did not improve the hydrogen evolution activity of our hydrogenase. However, modifying both the medial cluster and the ligation of the distal Fe-S cluster improved in vitro hydrogen evolution activity relative to the wild type hydrogenase by three- to four-fold. Other properties of the enzyme including thermostability and tolerance to partial oxygen did not appear to be affected by the substitutions. CONCLUSIONS:Our results show that substitution of amino acids altering the ligation of Fe-S clusters in the A. macleodii [NiFe] uptake hydrogenase resulted in increased hydrogen evolution activity. This activity can be recapitulated in multiple host systems and with purified protein. These results validate the approach of using an E. coli-cyanobacteria shuttle system for enzyme expression and improvement.

Dataset Information

Dual role of HupF in the biosynthesis of [NiFe] hydrogenase in Rhizobium leguminosarum.

Publications

Dual role of HupF in the biosynthesis of [NiFe] hydrogenase in Rhizobium leguminosarum.

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