• Journal of Life Science
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• v.16 no.3 s.76
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• pp.485-492
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• 2006

The PrrBA two-component system is one of the major regulatory systems that control expression of photosynthesis genes in response to changes in oxygen tension in the anoxygenic photosynthetic bacterium, Rhodobacter sphaeroides. The system consists of the PrrB histidine kinase and the PrrA response regulator. The N-terminal transmembrane domain of PrrB serves as a signal-sensing domain and comprises six transmembrane helices forming three periplasmic loops and two cytoplasmic loops. The $3^{rd}$ and $4^{th}$ transmembrane helices and the $2^{nd}$ periplasmic loop were suggested to play a crucial role in redox-sensory function. In this study we demonstrated that mutations of Asp-90, Gln-93, Leu-94, Leu-98, and Asn-106 in the $2^{nd}$ periplasmic loop and its neighboring region led to severe defects in PrrB sensory function, indicating that these amino acids might be related to the redox-sensing function of PrrB. The mutant forms (D90E, D90N, and D90A) of PrrB were heterologously overexpressed in Escherichia coli, purified by means of affinity chromatography and their autokinase activities were comparatively assessed. The D90N form of PrrB was shown to possess higher autokinase activity than the wild-type form of PrrB, whereas the D90E form of PrrB displayed lower autokinase activity than the wild-type form of PrrB. The D90A mutation led to the loss of PrrB autokinase activity.

• Journal of Life Science
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• v.19 no.7
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• pp.852-858
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• 2009

The homeostasis of the pyridine nucleotide pool [NAD(P)H and NAD(P)$^+$] is maintained in Rhodobacter sphaeroides mutant strains defective in the cytochrome bci complex or the cytochrome c oxidases in terms of its concentration and redox state. Aerobic derepression of the puf operon, which is under the control of the PrrBA two-component system, in the CBB3 mutant strain of R. sphaeroides was shown to be not the result of changes in the redox state of the pyridine nucleotides and the ubiquinone/ubiquinol pool. Using the bc$_1$ complex knock-out mutant strain of R. sphaeroides, we clearly demonstrated that the inhibitory effect of cbb$_3$, oxidase on spectral complex formation is not caused indirectly by the redox change of the ubiquinone/ubiquinol pool.

• Journal of Life Science
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• v.16 no.4
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• pp.632-639
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• 2006

Here we examined the expression patterns and regulation of seven photosynthesis (PS) genes (puf, puc, puhA, bchC, bchE, bchF, and bchI) in the anoxygenic photosynthetic bacterium, Rhodobacter sphaeroides, based on lacZ reporter gene assay. Expression of the tested PS genes, except puhA and bchI, were strongly induced in R. sphaeroides grown under anaerobic conditions relative to that under aerobic conditions. The puhA and bchI genes appear to form the operons together with bchFNBHLM-RSP0290 and crtA, respectively. Expression of the puf, puc, and bchCXYZ operons in R. sphaeroides grown photosynthetically was proportional to the incident light intensity, whereas that of bchFNBHLM(RSP0290-puhA) was inversely related to light intensity. Expression of bchEJG was lowest under medium-light photosynthetic conditions $(10\;W/m^2)$ and highest under high light conditions $(100\;W/m^2)$. The regulation of PS genes by the three major regulatory systems involved in oxygen- and light-sensing in R. sphaeroides is as following: puf and bchC are regulated by both the PpsR repressor and the PrrBA two-component system. The puc operon is under control of PpsR, FnrL, and PrrBA system. Expression of bchE is controlled by FnrL and PrrBA two-component system, whereas bchF is regulated exclusively by PpsR. It was demonstrated that the PpsR repressor is responsible for high-light repression of bchF and that FnrL might be involved in perceiving the cellular redox state in addition to sensing $O_2$ itself.

• Journal of Microbiology
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• v.44 no.3
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• pp.284-292
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• 2006

The cbb3 cytochrome c oxidase has the dual function as a terminal oxidase and oxygen sensor in the photosynthetic bacterium, Rhodobacter sphaeroides. The cbb3 oxidase forms a signal transduction pathway together with the PrrBA two-component system that controls photosynthesis gene expression in response to changes in oxygen tension in the environment. Under aerobic conditions the cbb3 oxidase generates an inhibitory signal, which shifts the equilibrium of PrrB kinase/phosphatase activities towards the phosphatase mode. Photosynthesis genes are thereby turned off under aerobic conditions. The catalytic subunit (CcoN) of the R. sphaeroides cbb3 oxidase contains five histidine residues (H2l4, B233, H303, H320, and H444) that are conserved in all CcoN subunits of the cbb3 oxidase, but not in the catalytic subunits of other members of copper-heme superfamily oxidases. H214A mutation of CcoN affected neither catalytic activity nor sensory (signaling) function of the cbb3 oxidase, whereas H320A mutation led to almost complete loss of both catalytic activity and sensory function of the cbb3 oxidase. H233V and H444A mutations brought about the partial loss of catalytic activity and sensory function of the cbb3 oxidase. Interestingly, the H303A mutant form of the cbb3 oxidase retains the catalytic function as a cytochrome c oxidase as compared to the wild-type oxidase, while it is defective in signaling function as an oxygen sensor. H303 appears to be implicated in either signal sensing or generation of the inhibitory signal to the PrrBA two-component system.

• Journal of Environmental Science International
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• v.21 no.9
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• pp.1139-1147
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• 2012

To find out the growth conditions for the maximum activity of nitrogenase which catalyzes nitrogen fixation in Rhodobacter sphaeroides, the promoter activities of nifA and nifH were analyzed and the results indicated that expression of both nifA and nifH was increased in response to deprivation of both O2 concentration and nitrogen source. The nifA mutant was constructed by deleting the gene to investigate the effect of NifA, the transcriptional regulator, on the nifH and nifA expression in R. sphaeroides. Analysis of expression of nif genes using the nifA::lacZ and nifH::lacZ fusions in the nifA mutant revealed that NifA acts as a positive activator for nifH and an autoregulator in its own expression. The promoter activities of nifA and nifH in the prrA mutant grown under anaerobic and ${NH_4}^+$-free conditions were derepressed, comparing with those of the wild-type grown under the same conditions, indicating that the prrA product acts as a positive regulator in expression of nifA and nifH.