title: Phototransformation of the red light sensor cyanobacterial phytochrome 2 from Synechocystis species depends on its tongue motifs.
abstract: Phytochromes are photoreceptors using a bilin tetrapyrrole as chromophore, which switch in canonical phytochromes between red (Pr) and far red (Pfr) light-absorbing states. Cph2 from Synechocystis sp., a noncanonical phytochrome, harbors besides a cyanobacteriochrome domain a second photosensory module, a Pr/Pfr-interconverting GAF-GAF bidomain (SynCph2(1-2)). As in the canonical phytochromes, a unique motif of the second GAF domain, the tongue region, seals the bilin-binding site in the GAF1 domain from solvent access. Time-resolved spectroscopy of the SynCph2(1-2) module shows four intermediates during Pr → Pfr phototransformation and three intermediates during Pfr → Pr back-conversion. A mutation in the tongue's conserved PRXSF motif, S385A, affects the formation of late intermediate R3 and of a Pfr-like state but not the back-conversion to Pr via a lumi-F-like state. In contrast, a mutation in the likewise conserved WXE motif, W389A, changes the photocycle at intermediate R2 and causes an alternative red light-adapted state. Here, back-conversion to Pr proceeds via intermediates differing from SynCph2(1-2). Replacement of this tryptophan that is ∼15 Å distant from the chromophore by another aromatic amino acid, W389F, restores native Pr → Pfr phototransformation. These results indicate large scale conformational changes within the tongue region of GAF2 during the final processes of phototransformation. We propose that in early intermediates only the chromophore and its nearest surroundings are altered, whereas late changes during R2 formation depend on the distant WXE motifs of the tongue region. Ser-385 within the PRXSF motif affects only late intermediate R3, when refolding of the tongue and docking to the GAF1 domain are almost completed.
authors.affiliation: From the Departments of Chemistry and Biology, Philipps-University, D-35032 Marburg and.
authors.forename: Katrin
authors.initials: K
authors.lastname: Anders
authors.affiliation: the Max-Planck Institute for Chemical Energy Conversion, D-45470 Mülheim a. d. Ruhr, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Gutt
authors.affiliation: the Max-Planck Institute for Chemical Energy Conversion, D-45470 Mülheim a. d. Ruhr, Germany wolfgang.gaertner@cec.mpg.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gärtner
authors.affiliation: From the Departments of Chemistry and Biology, Philipps-University, D-35032 Marburg and essen@chemie.uni-marburg.de.
authors.forename: Lars-Oliver
authors.initials: LO
authors.lastname: Essen
mesh_terms: D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001654:Bile Pigments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D008027:Light; D009154:Mutation; D020283:Photoreceptors, Microbial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010834:Phytochrome / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D012694:Serine / Q000737:chemistry; D046939:Synechocystis / Q000737:chemistry* / Q000378:metabolism; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D001654:Bile Pigments; C413622:Cph2 protein, bacteria; D020283:Photoreceptors, Microbial; D010834:Phytochrome; D012694:Serine; D014364:Tryptophan
keywords: Bacterial Signal Transduction; Bilin Chromophore; Cyanobacterial Phytochrome; Photo Intermediates; Photoreceptor; Protein Motif; Signaling; Time-resolved Spectroscopy; Tryptophan; Tryptophan Switch