Journal Article

Cyanobacterial Phytochrome-like PixJ1 Holoprotein Shows Novel Reversible Photoconversion Between Blue- and Green-absorbing Forms

Shizue Yoshihara, Mitsunori Katayama, Xiaoxing Geng and Masahiko Ikeuchi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 12, pages 1729-1737
Published in print December 2004 | ISSN: 0032-0781
Published online December 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch214
Cyanobacterial Phytochrome-like PixJ1 Holoprotein Shows Novel Reversible Photoconversion Between Blue- and Green-absorbing Forms

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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, λAmax = 425–435 nm) and a green light-absorbing form (Pg, λAmax = 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.

Keywords: Keywords: Cyanobacterium — Motility —Photoreceptor — Phototaxis — Phytochrome — Signal transduction.; Abbreviations: BV, biliverdin; PCB, phycocyanobilin; PΦB, phytochromobilin.

Journal Article.  6714 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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