NDLI: Posttranslational control of transcription factor FixK2, a key regulator for the Bradyrhizobium japonicum

Content Provider	PubMed Central
Author	Mesa, Socorro Reutimann, Luzia Fischer, Hans-martin Hennecke, Hauke
Abstract	Rhizobial FixK-like proteins play essential roles in activating genes for endosymbiotic life in legume root nodules, such as genes for micro-oxic respiration. In the facultative soybean symbiont, Bradyrhizobium japonicum, the FixK2 protein is the key player in a complex regulatory network. The fixK 2 gene itself is activated by the 2-component regulatory system FixLJ in response to a moderate decrease of the oxygen tension, and the FixK2 protein distributes and amplifies this response to the level of approximately 200 target genes. Unlike other members of the cAMP receptor protein family, to which FixK2 belongs, the FixK2 protein does not appear to be modulated by small effector molecules. Here, we show that a critical, single cysteine residue (C183) near the DNA-binding domain of FixK2 confers sensitivity to oxidizing agents and reactive oxygen species. Oxidation-dependent inactivation occurs not only in vitro, as shown with cell-free transcription assays, but also in vivo, as shown by microarray-assisted transcriptome analysis of the FixK2 regulon. The oxidation mechanism may involve a reversible dimerization by intermolecular disulfide-bridge formation and a direct, irreversible oxidation at the cysteine thiol, depending on the oxidizing agent. Mutational exchange of C183 to alanine renders FixK2 resistant to oxidation, yet allows full activity, shown again both in vitro and in vivo. We hypothesize that posttranslational modification by reactive oxygen species is a means to counterbalance the cellular pool of active FixK2, which would otherwise fill unrestrictedly through FixLJ-dependent synthesis.
Related Links	http://dx.doi.org/10.1073/pnas.0908097106
Ending Page	21865
Page Count	6
Starting Page	21860
File Format	PDF
ISSN	00278424
e-ISSN	10916490
Journal	Proceedings of the National Academy of Sciences of the United States of America
Issue Number	51
Volume Number	106
Language	English
Publisher	National Academy of Sciences
Publisher Date	2009-12-22
Access Restriction	Open
Rights Holder	National Academy of Sciences
Subject Keyword	General Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Multidisciplinary

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