Signal transduction to the Azotobacter vinelandii NIFL-NIFA regulatory system is influenced directly by interaction with 2-oxoglutarate and the PII regulatory protein.
PII-like signal transduction proteins, which respond to the nitrogen status via covalent modification and signal the carbon status through the binding of 2-oxoglutarate, have been implicated in the regulation of nitrogen fixation in several diazotrophs. The NIFL-NIFA two-component regulatory system, which integrates metabolic signals to fine-tune regulation of nitrogenase synthesis in Azotobacter vinelandii, is a potential target for PII-mediated signal transduction. Here we demonstrate that the inhibitory activity of the A.vinelandii NIFL protein is stimulated by interaction with the non-uridylylated form of PII-like regulatory proteins. We also observe that the NIFL-NIFA system is directly responsive to 2-oxoglutarate. We propose that the PII protein signals the nitrogen status by interaction with the NIFL-NIFA system under conditions of nitrogen excess, and that the inhibitory activity of NIFL is relieved by elevated levels of 2-oxoglutarate when PII is uridylylated under conditions of nitrogen limitation. Our observations suggest a model for signal transduction to the NIFL-NIFA system in response to carbon and nitrogen status which is clearly distinct from that suggested from studies on other diazotrophs.
Little
R
R
Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK.
Reyes-Ramirez
F
F
Zhang
Y
Y
van Heeswijk
W C
WC
Dixon
R
R
D000227:Adenine Nucleotides / Q000494:pharmacology; D016948:Azotobacter vinelandii / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D005798:Genes, Bacterial; D007656:Ketoglutaric Acids / Q000378:metabolism* / Q000494:pharmacology; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism; D010084:Oxidation-Reduction; D051922:PII Nitrogen Regulatory Proteins; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D000227:Adenine Nucleotides; D001426:Bacterial Proteins; D002352:Carrier Proteins; C113488:GlnK protein, Azorhizobium caulinodans; D007656:Ketoglutaric Acids; C061338:NifA protein, Bacteria; D051922:PII Nitrogen Regulatory Proteins; D014157:Transcription Factors; C084296:nifL protein, Bacteria; C404143:PIID regulatory protein, Bacteria; D002244:Carbon; D009584:Nitrogen