Role of GlnB and GlnK in ammonium control of both nitrogenase systems in the phototrophic bacterium Rhodobacter capsulatus.
In most bacteria, nitrogen metabolism is tightly regulated and P(II) proteins play a pivotal role in the regulatory processes. Rhodobacter capsulatus possesses two genes (glnB and glnK) encoding P(II)-like proteins. The glnB gene forms part of a glnB-glnA operon and the glnK gene is located immediately upstream of amtB, encoding a (methyl-) ammonium transporter. Expression of glnK is activated by NtrC under nitrogen-limiting conditions. The synthesis and activity of the molybdenum and iron nitrogenases of R. capsulatus are regulated by ammonium on at least three levels, including the transcriptional activation of nifA1, nifA2 and anfA by NtrC, the regulation of NifA and AnfA activity by two different NtrC-independent mechanisms, and the post-translational control of the activity of both nitrogenases by reversible ADP-ribosylation of NifH and AnfH as well as by ADP-ribosylation independent switch-off. Mutational analysis revealed that both P(II)-like proteins are involved in the ammonium regulation of the two nitrogenase systems. A mutation in glnB results in the constitutive expression of nifA and anfA. In addition, the post-translational ammonium inhibition of NifA activity is completely abolished in a glnB-glnK double mutant. However, AnfA activity was still suppressed by ammonium in the glnB-glnK double mutant. Furthermore, the P(II)-like proteins are involved in ammonium control of nitrogenase activity via ADP-ribosylation and the switch-off response. Remarkably, in the glnB-glnK double mutant, all three levels of the ammonium regulation of the molybdenum (but not of the alternative) nitrogenase are completely circumvented, resulting in the synthesis of active molybdenum nitrogenase even in the presence of high concentrations of ammonium.
Drepper
Thomas
T
Ruhr-Universität Bochum, Lehrstuhl für Biologie der Mikroorganismen, D-44780 Bochum, Germany.
Groß
Silke
S
Ruhr-Universität Bochum, Lehrstuhl für Biologie der Mikroorganismen, D-44780 Bochum, Germany.
Yakunin
Alexander F
AF
Université de Montréal, Département de microbiologie et immunologie, CP 6128, succursale Centre-ville, Montréal, Québec, Canada H3C 3J7.
Hallenbeck
Patrick C
PC
Université de Montréal, Département de microbiologie et immunologie, CP 6128, succursale Centre-ville, Montréal, Québec, Canada H3C 3J7.
Masepohl
Bernd
B
Ruhr-Universität Bochum, Lehrstuhl für Biologie der Mikroorganismen, D-44780 Bochum, Germany.
Klipp
Werner
W
Ruhr-Universität Bochum, Lehrstuhl für Biologie der Mikroorganismen, D-44780 Bochum, Germany.
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008954:Models, Biological; D008982:Molybdenum / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009154:Mutation; D009591:Nitrogenase / Q000235:genetics / Q000378:metabolism*; D051922:PII Nitrogen Regulatory Proteins; D011499:Protein Processing, Post-Translational; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D004269:DNA, Bacterial; C113488:GlnK protein, Azorhizobium caulinodans; C061338:NifA protein, Bacteria; D051922:PII Nitrogen Regulatory Proteins; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; C404143:PIID regulatory protein, Bacteria; D008982:Molybdenum; D009591:Nitrogenase