Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.13.3 (histidine kinase)
 2,405 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Over the last two decades, the biochemistry and genetics of dimethylsulfoxide (DMSO) and trimethylamine-N-oxide (TMAO) respiration has been characterised, particularly in Escherichia coli marine bacteria of the genus Shewanella and the purple phototrophic bacteria, Rhodobacter sphaeroides and R. capsulatus. All of the enzymes (or catalytic subunits) involved the final step in DMSO and TMAO respiration contain a pterin molybdenum cofactor and are members of the DMSO reductase family of molybdoenzymes. In E. coli, the dimethylsulfoxide reductase (DmsABC) can be purified from membranes as a complex, which exhibits quinol-DMSO oxidoreductase activity. The enzyme is anchored to the membrane via the DmsC subunit and its catalytic subunit DmsA is now considered to face the periplasm. Electron transfer to DmsA involves the DmsB subunit, which is a polyferredoxin related to subunits found in other molybdoenzymes such as nitrate reductase and formate dehydrogenase. A characteristic of the DmsAB-type DMSO reductase is its ability to reduce a variety of S- and N-oxides. E. coli contains a trimethylamine-N-oxide reductase (TorA) that is highly specific for N-oxides. This enzyme is located in the periplasm and is connected to the quinone pool via a membrane-bound penta-haem cytochrome (TorC). DorCA in purple phototrophic bacteria of the genus Rhodobacter is very similar to TorCA with the critical difference that DorA catalyses reduction of both DMSO and TMAO. It is known as a DMSO reductase because the S-oxide is the best substrate. Crystal structures of DorA and TorA have revealed critical differences at the Mo active site that may explain the differences between substrate specificity between the two enzymes. DmsA, TorA and DorA possess a "twin arginine" N-terminal signal sequence consistent with their secretion via the TAT secretory system and not the Sec system. The enzymes are secreted with their bound prosthetic groups: this take place in the cytoplasm and the biogenesis involves a chaperone protein, which is cognate for each enzyme. Expression of the DMSO and TMAO respiratory operons is induced in response to a fall in oxygen tension. dmsABC expression is positively controlled by the oxygen-responsive transcription factor, Fnr and ModE, a transcription factor that binds molybdate. In contrast, torCAD expression is not under Fnr- or ModE-control but is dependent upon a sensor histidine kinase-response regulator pair, TorSR, which activate gene expression under conditions of low oxygen tension in the presence of N- or S-oxide. Regulation of dorCDA expression is similar to that seen for torCAD but it appears that the expression of the sensor histidine kinase-response regulator pair, DorSR is regulated by Fnr and there is an additional tier of regulation involving the ModE-homologue MopB, molybdate and the transcription factor DorX. Analysis of microbial genomes has revealed the presence of dms and tor operons in a wide variety of bacteria and in some archaea and duplicate dms and tor operons have been identified in E. coli. Challenges ahead will include the determination of the significance of the presence of the dms operon in bacterial pathogens and the determination of the significance of DMSO respiration in the global turnover of marine organo-sulfur compounds.
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PMID:Microbial dimethylsulfoxide and trimethylamine-N-oxide respiration. 1622 80

Replicon architecture in bacteria is commonly comprised of one indispensable chromosome and several dispensable plasmids. This view has been enriched by the discovery of additional chromosomes, identified mainly by localization of rRNA and/or tRNA genes, and also by experimental demonstration of their requirement for cell growth. The genome of Rhizobium etli CFN42 is constituted by one chromosome and six large plasmids, ranging in size from 184 to 642 kb. Five of the six plasmids are dispensable for cell viability, but plasmid p42e is unusually stable. One possibility to explain this stability would be that genes on p42e carry out essential functions, thus making it a candidate for a secondary chromosome. To ascertain this, we made an in-depth functional analysis of p42e, employing bioinformatic tools, insertional mutagenesis, and programmed deletions. Nearly 11% of the genes in p42e participate in primary metabolism, involving biosynthetic functions (cobalamin, cardiolipin, cytochrome o, NAD, and thiamine), degradation (asparagine and melibiose), and septum formation (minCDE). Synteny analysis and incompatibility studies revealed highly stable replicons equivalent to p42e in content and gene order in other Rhizobium species. A systematic deletion analysis of p42e allowed the identification of two genes (RHE_PE00001 and RHE_PE00024), encoding, respectively, a hypothetical protein with a probable winged helix-turn-helix motif and a probable two-component sensor histidine kinase/response regulator hybrid protein, which are essential for growth in rich medium. These data support the proposal that p42e and its homologous replicons (pA, pRL11, pRLG202, and pR132502) merit the status of secondary chromosomes.
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PMID:Plasmids with a chromosome-like role in rhizobia. 2121 3

Variation in phenotypic traits that contribute to fitness influences a population's evolutionary response and its impact on ecosystem function following environmental change, yet its amount and nature are rarely known. Here, we investigated variation in nitrogen (N) fixation activity and its genetic basis for a random sample of laboratory strains of the cyanobacterium Mastigocladus laminosus from a N-limited, geothermally influenced stream in Yellowstone National Park. In a linear mixed-effects model, temperature and genetic differences among strains were the most important factors explaining variation in activity. Genome-wide analyses of genetic divergence between groups of strains that varied in N fixation activity revealed that few loci were strongly associated with these phenotypic differences. Notably, a single nonsynonymous polymorphism in the sulfate assimilation gene apsK explained >25% of the variation in activity at high temperature. We further identified a role for allelic variation of multiple terminal cytochrome oxidases for different aspects of N fixation. In addition, genomes of strains that fixed the most N overall contained a nonsense mutation in a histidine kinase gene that is expected to disrupt normal protein function and may result in transcriptional rewiring. This study illustrates how taking complementary approaches to link phenotype and genotype can inform our understanding of microbial population diversity.
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PMID:Genomics of variation in nitrogen fixation activity in a population of the thermophilic cyanobacterium Mastigocladus laminosus. 2750 45