title: Novel photosensory two-component system (PixA-NixB-NixC) involved in the regulation of positive and negative phototaxis of cyanobacterium Synechocystis sp. PCC 6803.
abstract: Two wild-type substrains of a motile cyanobacterium Synechocystis sp. PCC 6803 show positive phototaxis toward a light source (PCC-P) and negative phototaxis away from light (PCC-N). In this study, we found that a novel two-component system of photoresponse is involved in the phototactic regulation. Inactivation of slr1212 (pixA), which encodes a photoreceptor histidine kinase, reverted the positive phototaxis of PCC-P to negative phototaxis, and inactivation of the downstream slr1213 (nixB) and slr1214 (nixC), which encode AraC-like transcription factor-type and PatA-type response regulators, respectively, reverted the negative phototaxis of PCC-N to positive phototaxis. Opposite effects of pixA and nixBC disruption implies an unexpected signal transduction pathway in the switching of positive and negative phototaxis. The blue/green-type cyanobacteriochrome GAF domain of PixA was expressed in Synechocystis and phycocyanobilin-producing Escherichia coli. The holoprotein covalently bound a chromophore phycoviolobilin and showed reversible photoconversion between the violet- (Pv, λ(peak) = 396 nm) and green-absorbing (Pg, λ(peak) = 533 nm) forms, although the protein from E. coli partially bound a precursor phycocyanobilin. These results were discussed with regard to an idea that PixA serves as a violet light receptor for switching of positive and negative phototaxis by transcriptional and functional regulation.
authors: Department of Life Sciences (Biology), Graduate School of Art and Sciences, University of Tokyo, Komaba 3-8-1, Meguro, Tokyo, 153-8902 Japan. narikawa@bio.c.u-tokyo.ac.jp
authors: Rei
authors: R
authors: Narikawa
authors: Fumiko
authors: F
authors: Suzuki
authors: Shizue
authors: S
authors: Yoshihara
authors: Sho-ichi
authors: S
authors: Higashi
authors: Masakatsu
authors: M
authors: Watanabe
authors: Masahiko
authors: M
authors: Ikeuchi
mesh_terms: D000042:Absorption / Q000187:drug effects / Q000528:radiation effects; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001681:Biological Assay; D004926:Escherichia coli / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D008027:Light; D055537:Light Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000378:metabolism; D018524:Phototropism / Q000528:radiation effects; D052980:Phycobilins / Q000378:metabolism; D010798:Phycocyanin / Q000378:metabolism; D010802:Phylogeny; D011489:Protein Denaturation / Q000187:drug effects / Q000528:radiation effects; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification; D013057:Spectrum Analysis; D046939:Synechocystis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D014508:Urea / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; C471213:His-His-His-His-His-His; D009842:Oligopeptides; D052980:Phycobilins; D011993:Recombinant Fusion Proteins; D010798:Phycocyanin; C011069:phycocyanobilin; D006639:Histidine; D014508:Urea