title: Light-induced conformational changes of LOV1 (light oxygen voltage-sensing domain 1) and LOV2 relative to the kinase domain and regulation of kinase activity in Chlamydomonas phototropin.
abstract: Phototropin (phot), a blue light (BL) receptor in plants, has two photoreceptive domains named LOV1 and LOV2 as well as a Ser/Thr kinase domain (KD) and acts as a BL-regulated protein kinase. A LOV domain harbors a flavin mononucleotide that undergoes a cyclic photoreaction upon BL excitation via a signaling state in which the inhibition of the kinase activity by LOV2 is negated. To understand the molecular mechanism underlying the BL-dependent activation of the kinase, the photochemistry, kinase activity, and molecular structure were studied with the phot of Chlamydomonas reinhardtii. Full-length and LOV2-KD samples of C. reinhardtii phot showed cyclic photoreaction characteristics with the activation of LOV- and BL-dependent kinase. Truncation of LOV1 decreased the photosensitivity of the kinase activation, which was well explained by the fact that the signaling state lasted for a shorter period of time compared with that of the phot. Small angle x-ray scattering revealed monomeric forms of the proteins in solution and detected BL-dependent conformational changes, suggesting an extension of the global molecular shapes of both samples. Constructed molecular model of full-length phot based on the small angle x-ray scattering data proved the arrangement of LOV1, LOV2, and KD for the first time that showed a tandem arrangement both in the dark and under BL irradiation. The models suggest that LOV1 alters its position relative to LOV2-KD under BL irradiation. This finding demonstrates that LOV1 may interact with LOV2 and modify the photosensitivity of the kinase activation through alteration of the duration of the signaling state in LOV2.
authors.affiliation: From the Department of Biological Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Okajima
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Aihara
authors.forename: Yuki
authors.initials: Y
authors.lastname: Takayama
authors.forename: Mihoko
authors.initials: M
authors.lastname: Nakajima
authors.forename: Sachiko
authors.initials: S
authors.lastname: Kashojiya
authors.forename: Takaaki
authors.initials: T
authors.lastname: Hikima
authors.forename: Tomotaka
authors.initials: T
authors.lastname: Oroguchi
authors.forename: Amane
authors.initials: A
authors.lastname: Kobayashi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sekiguchi
authors.forename: Masaki
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Tomomi
authors.initials: T
authors.lastname: Suzuki
authors.forename: Akira
authors.initials: A
authors.lastname: Nagatani
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakasako
authors.forename: Satoru
authors.initials: S
authors.lastname: Tokutomi
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics; D008027:Light; D008958:Models, Molecular; D056949:Phototropins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D015398:Signal Transduction / Q000502:physiology / Q000528:radiation effects*; D014961:X-Ray Diffraction
chemical_list: D056949:Phototropins; D011494:Protein Kinases
keywords: Phosphorylation; Photoreceptors; Plant Biochemistry; Serine Threonine Protein Kinase; Spectroscopy; X-ray Scattering