title: Cyanobacteriochrome CcaS is the green light receptor that induces the expression of phycobilisome linker protein.
abstract: Cyanobacteriochromes are a newly recognized group of photoreceptors that are distinct relatives of phytochromes but are found only in cyanobacteria. A putative cyanobacteriochrome, CcaS, is known to chromatically regulate the expression of the phycobilisome linker gene (cpcG2) in Synechocystis sp. PCC 6803. In this study, we isolated the chromophore-binding domain of CcaS from Synechocystis as well as from phycocyanobilin-producing Escherichia coli. Both preparations showed the same reversible photoconversion between a green-absorbing form (Pg, lambda(max) = 535 nm) and a red-absorbing form (Pr, lambda(max) = 672 nm). Mass spectrometry and denaturation analyses suggested that Pg and Pr bind phycocyanobilin in a double-bond configuration of C15-Z and C15-E, respectively. Autophosphorylation activity of the histidine kinase domain in nearly full-length CcaS was up-regulated by preirradiation with green light. Similarly, phosphotransfer to the cognate response regulator, CcaR, was higher in Pr than in Pg. From these results, we conclude that CcaS phosphorylates CcaR under green light and induces expression of cpcG2, leading to accumulation of CpcG2-phycobilisome as a chromatic acclimation system. CcaS is the first recognized green light receptor in the expanded phytochrome superfamily, which includes phytochromes and cyanobacteriochromes.
authors.affiliation: Department of Life Sciences (Biology), University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
authors.forename: Yuu
authors.initials: Y
authors.lastname: Hirose
authors.forename: Takashi
authors.initials: T
authors.lastname: Shimada
authors.forename: Rei
authors.initials: R
authors.lastname: Narikawa
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Katayama
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D000458:Cyanobacteria / Q000737:chemistry*; D029968:Escherichia coli Proteins; D005786:Gene Expression Regulation / Q000528:radiation effects; D008027:Light; D008969:Molecular Sequence Data; D010766:Phosphorylation; D020283:Photoreceptors, Microbial / Q000235:genetics* / Q000502:physiology*; D052980:Phycobilins / Q000378:metabolism; D045524:Phycobilisomes; D010798:Phycocyanin / Q000378:metabolism; D017434:Protein Structure, Tertiary; D046939:Synechocystis / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D020283:Photoreceptors, Microbial; D052980:Phycobilins; D045524:Phycobilisomes; D010798:Phycocyanin; C011069:phycocyanobilin