Carl Bauer Laboratory: Regulating The Bacterial Photosystem In Response To Changes In Oxygen Tension

Regulating The Bacterial Photosystem In Response To Changes In Oxygen Tension

The RegA-RegB global regulatory cascade

Much of our efforts on the regulation of the bacterial photosystem have been centered on the two component regulators RegB-RegA from Rhodobacter capsulatus. RegB is a membrane-bound redox responding spanning sensor kinase and RegA is a DNA binding response regulator.

After identifying these components as major regulators of the photosystem, we subsequently established that the RegB-RegA cascade functions as major regulators of numerous physiological processes in R. capsulatus. For example, we have demonstrated that RegB-RegA controls synthesis of the photosystem, components of the respiratory chain including various cytochromes, ubiquinone etc, the hydrogenase complex, components of the carbon and nitrogen fixation pathways and various dehydrogenases. These studies involved both gene expression analyses in mutant cell lines as well as DNA binding studies on various promoters with isolated RegA (reviewed in Elsen et al., 2004)

Our recent efforts on the RegB-RegA system have been centered on biochemical analysis of redox sensing by RegB. One recent published study has demonstrated that RegB interacts with the quinone pool (Swem et al, 2006). Currently, we are investigating how binding of oxidized quinones inhibits autphosphorylation activity of RegB.

Fig. 2, Various systems that are regulated by the RegB-RegA cascade. Fig. 3 The membrane-spanning region of RegB is indicated by boxes, with the quinone binding loop indicated in red/black. The red residues are fully conserved among > 20 RegB homologs that are present in other species. Mutational analysis of these residues leads to constitutive autophosphorylation activity.

The CrtJ response

In addition to RegB-RegA, R. capsulatus also contains a second redox responsive regulatory system known as CrtJ. CrtJ functions as a repressor of bacteriochlorophyll, carotenoid light harvesting and cytochrome gene expression (Fig. 4).

Fig. 4. Regulation of photosystem gene expression by the aerobic repressor CrtJ.

Fig. 5. Redox responsive binding by the aerobic repressor CrtJ is stimulated when redox active Cys are oxidized.

Mutational and biochemical studies with isolated CrtJ have demonstrated that this protein contains a redox active Cys that affects its DNA binding activity (Masuda et al.,2002, Masuda and Bauer 2005) . When the redox active Cys is oxidized, it stimulates binding of CrtJ to target promoters and when reduced it inhibits binding.

Currently we are undertaking genetic and biochemical analysis of the role of CrtJ in controlling heme expression (Smart, Willet and Bauer 2005)

Relevant References:

Recent reviews

Elsen, S., L. Swem, D. Swem, & C. E. Bauer. 2004. RegB/RegA, a highly conserved redox-responding global regulatory system. Microbio. and Mol. Biol. Rev. 68, 263-279

Bauer, C. E. 2004. Regulation of photosystem synthesis in Rhodobacter capsulatus. Photosynth. Res . 80, 353-360

Redox papers

Swem, L. R., X. Gong, C.-A. Yu & C. E Bauer. 2005. RegB controls a diverse array of metabolic processes by monitoring the redox state of the ubiquinone pool. J. Biol. Chem . 281, 6768 - 6775.

Smart, J. L., Willet, J., & C. E. Bauer. 2004 . Identification of multiple regulators controlling heme biosynthesis in Rhodobacter capsulatus J. Mol. Biol . 342, 1171-1186

Swem, L., B. J. Kraft, D. L. Swem, A. T. Setterdahl, S. J. Masuda, D. B. Knaff , J. M. Zaleski & C, E, Bauer. 2003. Signal Transduction By The Global Regulator RegB Is Mediated By A Redox Active Cysteine. EMBO J . 22, 4699-4780

Masuda, S., Dong, C., D. Swem, A. T. Setterdahl, D. B. Knaff , & C. E. Bauer . 2002. Aerobic repression of photosystem synthesis through formation of an intramolecular disulfide bond in CrtJ. Proc. Natl. Acad. Sci.. USA 99, 7078-7083

Masuda, S. & C. E. Bauer. 2002. AppA is a blue-light photoreceptor that anti-represses photosynthesis gene expression in Rhodobacter sphaeroides Cell 110, 613-623. (Featured on cover)