Interactions between paralogous bacterial enhancer‐binding proteins enable metal‐dependent regulation of alternative nitrogenases in Azotobacter vinelandii. Issue 1 (29th June 2022)

• Record Type: Journal Article
• Authors: Appia‐Ayme, Corinne; Little, Richard; Chandra, Govind; de Oliveira Martins, Carlo; Bueno Batista, Marcelo; Dixon, Ray
• Is Part Of: Molecular microbiology. Volume 118:Issue 1/2(2022)
• Page Start: 105
• Page End: 124
• Publication Date: 2022-06-29
• Subjects: alternative nitrogenases -- bacterial enhancer‐binding proteins -- biological nitrogen fixation -- transcriptional regulation -- vanadium; Molecular microbiology -- Periodicals; 572.829
• DOI: 10.1111/mmi.14955
• Languages: English
• ISSNs: 0950-382X

Abstract

Abstract: All diazotrophic bacteria and archaea isolated so far utilise a nitrogenase enzyme‐containing molybdenum in the active site co‐factor to fix atmospheric dinitrogen to ammonia. However, in addition to the Mo‐dependent nitrogenase, some nitrogen‐fixing prokaryotes also express genetically distinct alternative nitrogenase isoenzymes, namely the V‐dependent and Fe‐only nitrogenases, respectively. Nitrogenase isoenzymes are expressed hierarchically according to metal availability and catalytic efficiency. In proteobacteria, this hierarchy is maintained via stringent transcriptional regulation of gene clusters by dedicated bacterial enhancer‐binding proteins (bEBPs). The model diazotroph Azotobacter vinelandii contains two paralogs of the vanadium nitrogenase activator VnfA (henceforth, VnfA1), designated VnfA2 and VnfA3, with unknown functions. Here we demonstrate that the VnfA1 and VnfA3 bEBPs bind to the same target promoters in the Azotobacter vinelandii genome and co‐activate a subset of genes in the absence of V, including the structural genes for the Fe‐only nitrogenase. Co‐activation is inhibited by the presence of V and is dependent on an accessory protein VnfZ that is co‐expressed with VnfA3. Our studies uncover a plethora of interactions between bEBPs required for nitrogen fixation, revealing the unprecedented potential for fine‐tuning the expression of alternative nitrogenases in response to metal availability. Abstract : In addition to using the conventional molybdenum nitrogenase to fix atmospheric nitrogen, some diazotrophic bacteria encode alternative nitrogenase isoenzymes, named the vanadium‐dependent and iron‐only nitrogenases respectively. Here we uncover a complex metal‐dependent regulatory network, which controls hierarchical expression of the alternative nitrogenases in Azotobacter vinelandii, through interactions between bacterial enhancer proteins that fine‐tune regulation of gene expression.