title: Cyanobacterial phytochrome-like PixJ1 holoprotein shows novel reversible photoconversion between blue- and green-absorbing forms.
abstract: The gene, pixJ1 (formerly pisJ1), is predicted to encode a phytochrome-like photoreceptor that is essential for positive phototaxis in the unicellular cyanobacterium Synechocystis sp. PCC 6803 [Yoshihara et al. (2000) Plant Cell Physiol. 41: 1299]. The PixJ1 protein was overexpressed as a fusion with a poly-histidine tag (His-PixJ1) and isolated from Synechocystis cells. A zinc-fluorescence assay suggested that a linear tetrapyrrole was covalently attached to the His-PixJ1 protein as a chromophore. His-PixJ1 showed novel photoreversible conversion between a blue light-absorbing form (Pb, lambdaAmax=425-435 nm) and a green light-absorbing form (Pg, lambdaAmax=535 nm). Dark incubation led Pg to revert to Pb, indicative of stability of the Pb form in darkness. Red or far-red light irradiation, which is effective for photochemical conversion of the known phytochromes, produced no change in the spectra of Pb and Pg forms. Site-directed mutagenesis revealed that a Cys-His motif in the second GAF domain of PixJ1 is responsible for binding of the chromophore. Possible chromophore species are discussed with regard to the novel photoconversion spectrum.
authors.affiliation: Department of Life Sciences (Biology), University of Tokyo, Komaba 3-8-1, Meguro, Tokyo, 153-8902 Japan.
authors.forename: Shizue
authors.initials: S
authors.lastname: Yoshihara
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Katayama
authors.forename: Xiaoxing
authors.initials: X
authors.lastname: Geng
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D003624:Darkness; D016680:Genome, Bacterial; D008027:Light; D020283:Photoreceptors, Microbial / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D010834:Phytochrome / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology / Q000528:radiation effects; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*; D045725:Tetrapyrroles / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; D045322:Photosynthetic Reaction Center Complex Proteins; D045725:Tetrapyrroles; D010834:Phytochrome