Fine‐tuning modulation of oxidation-mediated posttranslational control of Bradyrhizobium diazoefficiens FixK2 transcription factor

Sergio Parejo Trevino, Juan J. Cabrera Rodriguez, Andrea Jimenez-Levia, Laura Tomas-Gallardo, Eulogio J. Bedmar, Andrew J. Gates, Socorro Mesa

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FixK2 is a CRP/FNR‐type transcription factor that plays a central role in a sophisticated regulatory network for the anoxic, microoxic and symbiotic lifestyles of the soybean endosymbiont Bradyrhizobium diazoefficiens. Apart of the balanced expression of the fixK2 gene under microoxic conditions (induced by the two‐component regulatory system FixLJ and negatively auto‐repressed), FixK2 activity is posttranslationally controlled by proteolysis, and by oxidation of a singular cysteine residue (C183) near its DNA‐binding domain. To simulate permanent oxidation of FixK2, we replaced C183 for aspartic acid. Purified C183D FixK2 protein showed both low DNA binding and in vitro transcriptional activation from the promoter of the fixNOQP operon, required for respiration under symbiosis. However, in a B. diazoefficiens strain coding for C183D FixK2, expression of a fixNOQP’‐‘lacZ fusion was similar to that in the wild type, when both strains were grown microoxically. The C183D FixK2 encoding strain also showed a wild‐type phenotype in symbiosis with soybeans, and increased fixK2 gene expression levels and FixK2 protein abundance in cells. These two latter observations together with a global transcriptional profile of the microoxically cultured C183D FixK2 encoding strain suggest the existence of a finely tuned regulatory strategy to counterbalance the oxidation‐mediated inactivation of FixK2 in vivo.
Original languageEnglish
Article number5117
JournalInternational Journal of Molecular Sciences
Issue number9
Early online date4 May 2022
Publication statusPublished - May 2022


  • CRP/FNR proteins
  • in vitro transcription
  • microarrays
  • microoxia
  • protein–DNA interaction
  • rhizobia
  • symbiosis

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