title: Time-resolved detection of conformational changes in oat phytochrome A: time-dependent diffusion.
abstract: Conformational changes in oat phytochrome A (phy) in solution after photoexcitation of the red-absorbing form (Pr) were studied in time-domain by the pulsed laser-induced transient grating technique. It was found that the diffusion coefficient (D) of far-red-absorbing form (Pfr) of large phy (1.3 x 10(-11) m(2) s(-1)) is markedly reduced compared with that of Pr (5.8 x 10(-11) m(2) s(-1)). This large reduction indicates that the conformation of Pfr is significantly changed from that of Pr, so that the intermolecular interaction with water molecules increases. This change completes within 1 ms after the photoexcitation. On the other hand, D of Pr of intact phy (4.1 x 10(-11) m(2) s(-1)) first decreases upon photoexcitation to 0.89 x 10(-11) m(2) s(-1) within 1 ms and then gradually increases with a time constant of 100 ms to the value of Pfr, 1.7 x 10(-11) m(2) s(-1). This slower phase suggests that the conformation of the N-terminal region changes with 100 ms to decrease the intermolecular interaction with water after a global change in the large phy region. The increase of D was interpreted in terms of alpha-helix formation in the Pfr form from the random coil structure in the Pr form.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Eitoku
authors.forename: Xristo
authors.initials: X
authors.lastname: Zarate
authors.forename: Gennady V
authors.initials: GV
authors.lastname: Kozhukh
authors.forename: Jeong-Il
authors.initials: JI
authors.lastname: Kim
authors.forename: Pill-Soon
authors.initials: PS
authors.lastname: Song
authors.forename: Masahide
authors.initials: M
authors.lastname: Terazima
mesh_terms: D018554:Avena / Q000737:chemistry* / Q000528:radiation effects; D004058:Diffusion; D004307:Dose-Response Relationship, Radiation; D008027:Light; D051942:Phytochrome A / Q000737:chemistry* / Q000528:radiation effects*; D011487:Protein Conformation / Q000528:radiation effects; D011829:Radiation Dosage
chemical_list: D051942:Phytochrome A