Phosphorylation, dephosphorylation and DNA-binding of the Bradyrhizobium japonicum RegSR two-component regulatory proteins.
Under low oxygen conditions, induction of many genes required for nitrogen fixation in Bradyrhizobium japonicum depends on the redox-responsive transcriptional activator NifA which is encoded in the fixR-nifA operon. Basal expression of this operon depends on the response regulator RegR and a DNA element located around position -68 in the fixR-nifA promoter region. To investigate the functional properties of RegR and the interaction with its putative cognate kinase, RegS, we overproduced and affinity-purified RegR and a truncated soluble variant of RegS (RegS(C)), both as N-terminally His(6)-tagged proteins. RegS(C) autophosphorylated when incubated with [gamma-(32)P]ATP, and it catalyzed the transfer of the phosphoryl label to RegR. The phosphorylated form of RegS(C) exhibited phosphatase activity on RegR-phosphate. Chemical stability tests and site-specific mutagenesis identified amino acids H219 and D63 of RegS and RegR, respectively, as the phosphorylated residues. Competition experiments with isolated domains demonstrated that the N-terminal but not the C-terminal domain of RegR interacts with RegS(C). Band-shift experiments revealed that phosphorylated RegR had at least eightfold enhanced DNA-binding activity compared with dephosphorylated RegR or the mutant protein RegR-D63N, which cannot be phosphorylated. In conclusion, the RegSR proteins of B. japonicum exhibit functional properties in vitro that are typical of two-component regulatory systems.
Mikrobiologisches Institut, Eidgenössische Technische Hochschule, Zürich, Switzerland.
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Emmerich
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Panglungtshang
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Strehler
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Hennecke
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Fischer
D001426:Bacterial Proteins; D020369:Bradyrhizobium / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000737:chemistry; D008954:Models, Biological; D016296:Mutagenesis; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000737:chemistry; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; C113722:RegR protein, bacteria; D014157:Transcription Factors