ADP‐ribosylation of dinitrogenase reductase in Azospirillum brasilense is regulated by AmtB‐dependent membrane sequestration of DraG

• Published in: Molecular microbiology 2006-01, Vol.59 (1), p.326-337
• Main Authors: Huergo, Luciano F., Souza, Emanuel M., Araujo, Mariana S., Pedrosa, Fábio O., Chubatsu, Leda S., Steffens, Maria B. R., Merrick, Mike
• Format: Article
• Language: English
• Subjects: Adenosine Diphosphate Ribose - metabolism; Ammonia; Azospirillum brasilense; Azospirillum brasilense - cytology; Azospirillum brasilense - enzymology; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biochemistry; Biological and medical sciences; Cation Transport Proteins - genetics; Cation Transport Proteins - metabolism; Cell Membrane - enzymology; Enzymes; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Glutamate-Ammonia Ligase - genetics; Glutamate-Ammonia Ligase - metabolism; Membrane separation; Microbiology; Miscellaneous; Molecular biology; N-Glycosyl Hydrolases - genetics; N-Glycosyl Hydrolases - metabolism; Nitrogen; Oxidoreductases - genetics; Oxidoreductases - metabolism; PII Nitrogen Regulatory Proteins - genetics; PII Nitrogen Regulatory Proteins - metabolism; Protein Processing, Post-Translational; Quaternary Ammonium Compounds - chemistry; Quaternary Ammonium Compounds - metabolism
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2005.04944.x

Summary Nitrogen fixation in some diazotrophic bacteria is regulated by mono‐ADP‐ribosylation of dinitrogenase reductase (NifH) that occurs in response to addition of ammonium to the extracellular medium. This process is mediated by dinitrogenase reductase ADP‐ribosyltransferase (DraT) and reversed by dinitrogenase reductase glycohydrolase (DraG), but the means by which the activities of these enzymes are regulated are unknown. We have investigated the role of the PII proteins (GlnB and GlnZ), the ammonia channel protein AmtB and the cellular localization of DraG in the regulation of the NifH‐modification process in Azospirillum brasilense. GlnB, GlnZ and DraG were all membrane‐associated after an ammonium shock, and both this membrane sequestration and ADP‐ribosylation of NifH were defective in an amtB mutant. We now propose a model in which membrane association of DraG after an ammonium shock creates a physical separation from its cytoplasmic substrate NifH thereby inhibiting ADP‐ribosyl‐removal. Our observations identify a novel role for an ammonia channel (Amt) protein in the regulation of bacterial nitrogen metabolism by mediating membrane sequestration of a protein other than a PII family member. They also suggest a model for control of ADP‐ribosylation that is likely to be applicable to all diazotrophs that exhibit such post‐translational regulation of nitrogenase.