Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the diazotroph Klebsiella pneumoniae the flavoprotein NifL inhibits the activity of the nif-specific transcriptional activator NifA in response to molecular oxygen and combined nitrogen. Sequestration of reduced NifL to the cytoplasmic membrane under anaerobic and nitrogen-limited conditions impairs inhibition of cytoplasmic NifA by NifL. To analyze whether NifL is reduced by electrons directly derived from the reduced menaquinone pool, we studied NifL reduction using artificial membrane systems containing purified components of the anaerobic respiratory chain of Wolinella succinogenes. In this in vitro assay using proteoliposomes containing purified formate dehydrogenase and purified menaquinone (MK(6)) or 8-methylmenaquinone (MMK(6)) from W. succinogenes, reduction of purified NifL was achieved by formate oxidation. Furthermore, the respective reduction rates, which were determined using equal amounts of NifL, have been shown to be directly dependent on the concentration of both formate dehydrogenase and menaquinones incorporated into the proteoliposomes, demonstrating a direct electron transfer from menaquinone to NifL. When purified hydrogenase and MK(6) from W. succinogenes were inserted into the proteoliposomes, NifL was reduced with nearly the same rate by hydrogen oxidation. In both cases reduced NifL was found to be highly associated to the proteoliposomes, which is in accordance with our previous findings in vivo. On the bases of these experiments, we propose that the redox state of the menaquinone pool is the redox signal for nif regulation in K. pneumoniae by directly transferring electrons onto NifL under anaerobic conditions.
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PMID:Biochemical studies of Klebsiella pneumoniae NifL reduction using reconstituted partial anaerobic respiratory chains of Wolinella succinogenes. 1732 51

Escherichia coli growing under anaerobic conditions produce H(2) and CO(2) by the enzymatic cleavage of formate that is produced from pyruvate at the end of glycolysis. Selenium is an integral part of formate dehydrogenase H (FDH H), which catalyses the first step in the formate hydrogen lyase (FHL) system. The genes of FHL system are transcribed only under anaerobic conditions, in the presence of a sigma 54-dependent transcriptional activator FhlA that binds formate as an effector molecule. Although the formate addition to the nutrient media has been an established procedure for inducing high FDH H activity, we have identified a low-salt nutrient medium containing <0.1% NaCl enabled constitutive, high expression of FDH H even without formate and d-glucose added to the medium. The novel conditions allowed us to study the effects of disrupting genes like trxB (thioredoxin reductase) or gor (glutathione reductase) on the production of FDH H activity and also reductive assimilation of selenite ( SeO 3(2-)) into the selenoprotein. Despite the widely accepted hypothesis that selenite is reduced by glutathione reductase-dependent system, it was demonstrated that trxB gene was essential for FDH H production and for labelling the FDH H polypeptide with 75Se-selenite. Our present study reports for the first time the physiological involvement of thioredoxin reductase in the reductive assimilation of selenite in E. coli.
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PMID:Selenite assimilation into formate dehydrogenase H depends on thioredoxin reductase in Escherichia coli. 1818 86

Escherichia coli produces H(2) from formate via the formate hydrogenlyase (FHL) complex during mixed acid fermentation; the FHL complex consists of formate dehydrogenase H (encoded by fdhF) for forming 2H(+), 2e(-), and CO(2) from formate and hydrogenase 3 (encoded by hycGE) for synthesizing H(2) from 2H(+) and 2e(-). FHL protein production is activated by the sigma(54) transcriptional activator FhlA, which activates transcription of fdhF and the hyc, hyp, and hydN-hypF operons. Here, through random mutagenesis using error-prone PCR over the whole gene, as well as over the fhlA region encoding the first 388 amino acids of the 692-amino-acid protein, we evolved FhlA to increase H(2) production. The amino acid replacements in FhlA133 (Q11H, L14V, Y177F, K245R, M288K, and I342F) increased hydrogen production ninefold, and the replacements in FhlA1157 (M6T, S35T, L113P, S146C, and E363K) increased hydrogen production fourfold. Saturation mutagenesis at the codons corresponding to the amino acid replacements in FhlA133 and at position E363 identified the importance of position L14 and of E363 for the increased activity; FhlA with replacements L14G and E363G increased hydrogen production (fourfold and sixfold, respectively) compared to FhlA. Whole-transcriptome and promoter reporter constructs revealed that the mechanism by which the FhlA133 changes increase hydrogen production is by increasing transcription of all of the genes activated by FhlA (the FHL complex). With FhlA133, transcription of P(fdhF) and P(hyc) is less sensitive to formate regulation, and with FhlA363 (E363G), P(hyc) transcription increases but P(hyp) transcription decreases and hydrogen production is less affected by the repressor HycA.
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PMID:Protein engineering of the transcriptional activator FhlA To enhance hydrogen production in Escherichia coli. 1958 79


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