The PpaA/AerR Regulators of Photosynthesis Gene Expression from Anoxygenic Phototrophic Proteobacteria Contain Heme-Binding SCHIC Domains

Moskvin, Oleg V.; Gilles-Gonzalez, Marie Alda; Gomelsky, Mark

doi:10.1128/jb.00736-10

Cited by 17 publications

(20 citation statements)

References 23 publications

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“…PpaA from R. sphaeroides was previously reported to be a hemebinding protein (31). However, our analysis shows that R. sphaeroides PpaA selectively and effectively binds OH-Cbl over both heme and other forms of cobalamin that contain a more tightly bound upper ligand.…”

Section: Discussioncontrasting

confidence: 42%

“…3), indicating that a fraction of heme may be coordinating with His146. This histidine, however, is not essential for heme binding, as was hypothesized by Moskvin et al (31), as some heme binding still occurs in the H146A mutant form. The G149E mutant form, which mimics the sequence found in the heme-binding AppA SCHIC domain, exhibits more pronounced heme binding, as evidence by an increase in the 412-nm heme peak over that observed with wild-type PpaA (Fig.…”

Section: R Sphaeroides Ppaa Binds Hydroxylcobalaminmentioning

confidence: 69%

“…A previous study by Moskvin et al (31) suggested that PpaA from R. sphaeroides is a heme-binding protein that is unable to bind cobalamin. However, in their experiments, they used a truncated variant of PpaA that contained just a region with homology Hydroxycobalamin was added to cell lysate at a final concentration of 25 M. Wild-type PpaA copurifies with cobalamin, while truncated (L248Stop) or single-residue mutant proteins all lost the ability to bind hydroxycobalamin.…”

Section: R Sphaeroides Ppaa Binds Hydroxylcobalaminmentioning

confidence: 99%

“…Phylogenetic analysis indicates that the B 12 -binding domain in PpaA/AerR homologs exhibit a notable evolutionary distance from that of B 12 -dependent enzymes, leading to the hypothesis that this family no longer binds cobalamin but instead may bind heme (30). Indeed, a study on a truncated B 12 -binding domain from R. sphaeroides PpaA showed a preference for the binding of heme over cobalamin like that of the related light-regulated antirepressor AppA (31). However, recently work by Cheng and coworkers showed that full-length AerR from R. capsulatus is, in fact, a bona fide cobalamin-binding protein that can be readily purified with tightly bound hydroxylcobalamin (29).…”

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confidence: 99%

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Members of the PpaA/AerR Antirepressor Family Bind Cobalamin

Vermeulen

Bauer

2015

J Bacteriol

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PpaA from Rhodobacter sphaeroides is a member of a family of proteins that are thought to function as antirepressors of PpsR, a widely disseminated repressor of photosystem genes in purple photosynthetic bacteria. PpaA family members exhibit sequence similarity to a previously defined SCHIC (sensor containing heme instead of cobalamin) domain; however, the tetrapyrrolebinding specificity of PpaA family members has been unclear, as R. sphaeroides PpaA has been reported to bind heme while the Rhodobacter capsulatus homolog has been reported to bind cobalamin. In this study, we reinvestigated tetrapyrrole binding of PpaA from R. sphaeroides and show that it is not a heme-binding protein but is instead a cobalamin-binding protein. We also use bacterial two-hybrid analysis to show that PpaA is able to interact with PpsR and activate the expression of photosynthesis genes in vivo. Mutations in PpaA that cause loss of cobalamin binding also disrupt PpaA antirepressor activity in vivo. We also tested a number of PpaA homologs from other purple bacterial species and found that cobalamin binding is a conserved feature among members of this family of proteins. IMPORTANCECobalamin (vitamin B 12 ) has only recently been recognized as a cofactor that affects gene expression by interacting in a lightdependent manner with transcription factors. A group of related antirepressors known as the AppA/PpaA/AerR family are known to control the expression of photosynthesis genes in part by interacting with either heme or cobalamin. The specificity of which tetrapyrroles that members of this family interact with has, however, remained cloudy. In this study, we address the tetrapyrrole-binding specificity of the PpaA/AerR subgroup and establish that it preferentially binds cobalamin over heme.

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Section: Discussioncontrasting

confidence: 42%

Section: R Sphaeroides Ppaa Binds Hydroxylcobalaminmentioning

confidence: 69%

Section: R Sphaeroides Ppaa Binds Hydroxylcobalaminmentioning

confidence: 99%

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confidence: 99%

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Members of the PpaA/AerR Antirepressor Family Bind Cobalamin

Vermeulen

Bauer

2015

J Bacteriol

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“…Also, no effect was seen with hemin ( Fig. S2C), which has been reported to bind to some proteins involved in redox-light sensing that have a B 12 -binding motif (28)(29)(30). By contrast, AdoB 12 enhanced DNA binding by CTt1 and, even more dramatically, by CTt2: a single, well defined, low-mobility retarded complex was now formed, with little or no free probe detected (Fig.…”

Section: Resultsmentioning

confidence: 94%

Light-dependent gene regulation by a coenzyme B ₁₂ -based photoreceptor

Ortiz-Guerrero

Polanco

Murillo

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

157

247

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Cobalamin (B 12 ) typically functions as an enzyme cofactor but can also regulate gene expression via RNA-based riboswitches. B 12 -directed gene regulatory mechanisms via protein factors have, however, remained elusive. Recently, we reported down-regulation of a light-inducible promoter in the bacterium Myxococcus xanthus by two paralogous transcriptional repressors, of which one, CarH, but not the other, CarA, absolutely requires B 12 for activity even though both have a canonical B 12 -binding motif. Unanswered were what underlies this striking difference, what is the specific cobalamin used, and how it acts. Here, we show that coenzyme B 12 (5′-deoxyadenosylcobalamin, AdoB 12 ), specifically dictates CarH function in the dark and on exposure to light. In the dark, AdoB 12 -binding to the autonomous domain containing the B 12 -binding motif foments repressor oligomerization, enhances operator binding, and blocks transcription. Light, at various wavelengths at which AdoB 12 absorbs, dismantles active repressor oligomers by photolysing the bound AdoB 12 and weakens repressor-operator binding to allow transcription. By contrast, AdoB 12 alters neither CarA oligomerization nor operator binding, thus accounting for its B 12 -independent activity. Our findings unveil a functional facet of AdoB 12 whereby it serves as the chromophore of a unique photoreceptor protein class acting in light-dependent gene regulation. The prevalence of similar proteins of unknown function in microbial genomes suggests that this distinct B 12 -based molecular mechanism for photoregulation may be widespread in bacteria.carotenogenesis | Thermus thermophilus | antirepressor | MerR | TtCarH

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