Integration of nitrogen, carbon and redox status by the Azotobacter vinelandii NifL-NifA regulatory complex

摘要

The Azotobacter vinelandii NifL-NifA two-component regulatory system integrates metabolic signals for redox, carbon and nitrogen status to fine tune regulation of nitrogenase synthesis (Dixon 1998). The NifL protein utilizes discrete mechanisms to perceive these signals leading to the formation of a protein-protein complex which inhibits NifA activity. The binding of adenosine nucleotides to NifL plays a key role in transducing environmental signals to form the inhibitory protein complex (Eydmann et al. 1995; Money et al. 1999). We have recently demonstrated that an additional ligand, 2-oxoglutarate, allosterically modulates the activity of the complex to antagonize the influence of adenosine nucleotides on NifL activity (Little et al. 2000). Redox signaling is mediated by the N-terminal FAD-containing PAS domain in NifL (Soderback et al. 1998) and the nitrogen status is sensed via interaction with the non-modified form of the PII-like signal transduction protein (Av GlnK) (Little et al. 2000) encoded by A. vinelandii glnK gene (Meletzus et al. 1998).