Effect of ATP and 2-oxoglutarate on the in vitro interaction between the NifA GAF domain and the GlnB protein of Azospirillum brasilense

• Main Author: Sotomaior,P.
• Publication Date: 2012
• Other Authors: Araújo,L.M., Nishikawa,C.Y., Huergo,L.F., Monteiro,R.A., Pedrosa,F.O., Chubatsu,L.S., Souza,E.M.
• Format: Article
• Language: eng
• Source: Brazilian Journal of Medical and Biological Research
• Download full: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2012001200005
• topic: Azospirillum brasilense; NifA protein; GlnB protein; GAF domain; Nitrogen fixation

Azospirillum brasilense is a diazotroph that associates with important agricultural crops and thus has potential to be a nitrogen biofertilizer. The A. brasilense transcription regulator NifA, which seems to be constitutively expressed, activates the transcription of nitrogen fixation genes. It has been suggested that the nitrogen status-signaling protein GlnB regulates NifA activity by direct interaction with the NifA N-terminal GAF domain, preventing the inhibitory effect of this domain under conditions of nitrogen fixation. In the present study, we show that an N-terminal truncated form of NifA no longer required GlnB for activity and lost regulation by ammonium. On the other hand, in trans co-expression of the N-terminal GAF domain inhibited the N-truncated protein in response to fixed nitrogen levels. We also used pull-down assays to show in vitro interaction between the purified N-terminal GAF domain of NifA and the GlnB protein. The results showed that A. brasilense GlnB interacts directly with the NifA N-terminal domain and this interaction is dependent on the presence of ATP and 2-oxoglutarate.