title: A haem cofactor is required for redox and light signalling by the AppA protein of Rhodobacter sphaeroides.
abstract: The AppA protein of Rhodobacter sphaeroides is unique in its ability to sense and transmit redox signals as well as light signals. By functioning as antagonist to the PpsR transcriptional repressor, it regulates the expression of photosynthesis genes in response to these environmental stimuli. Here we show binding of the cofactor haem to a domain in the C-terminal part of AppA and redox activity of bound haem. This is supported by the findings that: (i) the C-terminal domain of AppA (AppADeltaN) binds to haemin agarose, (ii) AppADeltaN isolated from Escherichia coli shows absorbance at 411 nm and absorbances at 424 nm and 556 nm after reduction with dithionite and (iii) AppADeltaN can be reconstituted with haem in vitro. Expression of AppA variants in R. sphaeroides reveals that the haem binding domain is important for normal expression levels of photosynthesis genes and for normal light regulation in the presence of oxygen. The haem cofactor affects the interaction of the C-terminal part of AppA to PpsR but also its interaction to the N-terminal light sensing AppA-BLUF domain. Based on this we present a model for the transmission of light and redox signals by AppA.
authors.affiliation: Institut für Mikrobiologie und Molekularbiologie, University of Giessen, D-35392 Giessen, Germany.
authors.forename: Yuchen
authors.initials: Y
authors.lastname: Han
authors.forename: Martin H F
authors.initials: MH
authors.lastname: Meyer
authors.forename: Michael
authors.initials: M
authors.lastname: Keusgen
authors.forename: Gabriele
authors.initials: G
authors.lastname: Klug
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D003067:Coenzymes / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D004926:Escherichia coli / Q000235:genetics; D005420:Flavoproteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D006418:Heme / Q000378:metabolism* / Q000494:pharmacology*; D006427:Hemin / Q000378:metabolism; D008027:Light; D008954:Models, Biological; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification; D012097:Repressor Proteins / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017384:Sequence Deletion; D015398:Signal Transduction; D013057:Spectrum Analysis
chemical_list: C116785:AppA protein, Rhodobacter sphaeroides; D001426:Bacterial Proteins; D003067:Coenzymes; D004268:DNA-Binding Proteins; D005420:Flavoproteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D006418:Heme; D006427:Hemin