title: Transient conformational fluctuation of TePixD during a reaction.
abstract: Knowledge of the dynamical behavior of proteins, and in particular their conformational fluctuations, is essential to understanding the mechanisms underlying their reactions. Here, transient enhancement of the isothermal partial molar compressibility, which is directly related to the conformational fluctuation, during a chemical reaction of a blue light sensor protein from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 (TePixD, Tll0078) was investigated in a time-resolved manner. The UV-Vis absorption spectrum of TePixD did not change with the application of high pressure. Conversely, the transient grating signal intensities representing the volume change depended significantly on the pressure. This result implies that the compressibility changes during the reaction. From the pressure dependence of the amplitude, the compressibility change of two short-lived intermediate (I1 and I2) states were determined to be +(5.6 ± 0.6) × 10(-2) cm(3) ⋅ mol(-1) ⋅ MPa(-1) for I1 and +(6.6 ± 0.7) × 10(-2) cm(3) ⋅ mol(-1) ⋅ MPa(-1) for I2. This result showed that the structural fluctuation of intermediates was enhanced during the reaction. To clarify the relationship between the fluctuation and the reaction, the compressibility of multiply excited TePixD was investigated. The isothermal compressibility of I1 and I2 intermediates of TePixD showed a monotonic decrease with increasing excitation laser power, and this tendency correlated with the reactivity of the protein. This result indicates that the TePixD decamer cannot react when its structural fluctuation is small. We concluded that the enhanced compressibility is an important factor for triggering the reaction of TePixD. To our knowledge, this is the first report showing enhanced fluctuations of intermediate species during a protein reaction, supporting the importance of fluctuations.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan;
authors.forename: Kunisato
authors.initials: K
authors.lastname: Kuroi
authors.affiliation: Department of Life Sciences (Biology), Graduate School of Arts and Sciences, University of Tokyo, Meguro, Tokyo 153-8902, Japan; and Research Institute for Advanced Science and Technology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Okajima
authors.affiliation: Department of Life Sciences (Biology), Graduate School of Arts and Sciences, University of Tokyo, Meguro, Tokyo 153-8902, Japan; and.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
authors.affiliation: Research Institute for Advanced Science and Technology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Tokutomi
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan; mterazima@kuchem.kyoto-u.ac.jp.
authors.forename: Masahide
authors.initials: M
authors.lastname: Terazima
mesh_terms: D065966:Absorption, Physicochemical; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism*; D007834:Lasers; D055668:Photochemical Processes; D011312:Pressure; D011487:Protein Conformation
chemical_list: D001426:Bacterial Proteins