Nakasone Yusuke, Ono Taka-aki, Ishii Asako, Masuda Shinji, Terazima Masahide
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan.
J Am Chem Soc. 2007 Jun 6;129(22):7028-35. doi: 10.1021/ja065682q. Epub 2007 May 10.
The photochemical reaction dynamics of YcgF, a BLUF protein, were investigated by the pulsed laser-induced transient grating (TG) technique. The TG signal showed three reaction time constants: 2.7 micros, 13 micros, and 2 ms. The fastest was tentatively attributed to relaxation of the excited triplet state of the chromophore, flavin adenine dinucleotide (FAD), and the others represented conformational changes of the protein. The TG signal provided clear evidence that the diffusion coefficient (D) of the photoproduct (3.8x10(-11) m2 s-1) was significantly less than that of the reactant (8.3x10(-11) m2 s-1), with a time constant of 2 ms at a protein concentration of 700 microM. Interestingly, the rate constant increased in proportion to the concentration of the protein, indicating that protein dimerization was one of the main reactions occurring after photoexcitation. The significant reduction in D indicates that a conformational change leading to an increase in interactions with water molecules occurs upon formation of the signaling state. The 13 mus dynamics was attributed to the conformational change that induced transient dimerization. This conformational change might be an essential process for the creation of the signaling state. A detailed scheme for the photochemical reaction of YcgF is proposed.
通过脉冲激光诱导瞬态光栅（TG）技术研究了蓝光感应类黄素蛋白（BLUF蛋白）YcgF的光化学反应动力学。TG信号显示出三个反应时间常数：2.7微秒、13微秒和2毫秒。最快的时间常数初步归因于发色团黄素腺嘌呤二核苷酸（FAD）激发三重态的弛豫，其他时间常数则代表蛋白质的构象变化。TG信号提供了明确的证据，表明在蛋白质浓度为700微摩尔时，光产物的扩散系数（D）（3.8×10⁻¹¹平方米·秒⁻¹）明显小于反应物的扩散系数（8.3×10⁻¹¹平方米·秒⁻¹），时间常数为2毫秒。有趣的是，速率常数与蛋白质浓度成正比增加，表明蛋白质二聚化是光激发后发生的主要反应之一。D的显著降低表明，在信号状态形成时，会发生构象变化，导致与水分子的相互作用增加。13微秒的动力学归因于诱导瞬态二聚化的构象变化。这种构象变化可能是形成信号状态的一个重要过程。本文提出了YcgF光化学反应的详细方案。
