Simultaneous analyses of the rates of photoinduced charge separation and recombination between the excited flavin and tryptophans in some flavoproteins: Molecular dynamics simulation
Simultaneous analyses of the rates of photoinduced charge separation and recombination between the excited flavin and tryptophans in some flavoproteins: Molecular dynamics simulation
复制标题
DOI：
10.1063/5.0014718
复制
发表时间：
2020-10-01
期刊：
影响因子：
1.6
通讯作者：
Chosrowjan, Haik
中科院分区：
文献类型：
--
作者：
Lugsanangarm, Kiattisak;Tamaoki, Haruhiko;Chosrowjan, Haik
超快瞬态吸收（TA）光谱是研究植物光合和黄素光感受器系统光诱导电子转移（ET）机制的最有力的实验工具之一。然而，还没有关于其定量机制的工作报告。据报道，在中链酰基辅酶A脱氢酶（MCAD）中，从色氨酸（Trps）到激发的异咯嗪（Iso*）的电荷分离（CS）和从所产生的离子对到处于基态的色氨酸和Iso的电荷重组（CR）的表观速率为0.25 ps和3.2 ps，在黄素单甘肽结合蛋白（FMN-bp）中为0.15 ps和6.6 ps，通过超快TA方法获得。首次用ET理论和分子动力学模拟得到的结构同时分析了CS和CR过程的衰变。MCAD和FMN-bp分别形成四聚体和二聚体。数值计算了单个供体的CS和CR率以及各种相关物理量。发现MCAD中4种Trp中Trp 166的CS和CR率最快，FMN-bp中2种Trp中Trp 106的CS和CR率最快。MCAD的CS率的对数与受体-供体距离（Rc）呈抛物线关系，CR率的对数与Rc呈线性关系。根据指数前因子理论，阐明了MCAD和FMN-bp的CS率比CR率快的原因。本方法有助于理解植物光感受器生物学功能起始阶段的确切机制。
Ultrafast transient absorption (TA) spectroscopy has been one of the most powerful experimental tools to study the mechanism of photoinduced electron transfer (ET) as in photosynthetic and flavin photoreceptor systems in plants. However, no work has been reported on their quantitative mechanisms. Apparent rates of charge separation (CS) from tryptophans (Trps) to the excited isoalloxazine (Iso*) and charge recombination (CR) from the produced ion pairs to Trps and Iso in the ground states are reported to be 0.25 ps and 3.2 ps in medium-chain acyl-CoA dehydrogenase (MCAD), and 0.15 ps and 6.6 ps in flavin mononucleotide binding protein (FMN-bp), obtained by an ultrafast TA method. The decays of the CS and CR processes were for the first time simultaneously analyzed with an ET theory and structures obtained by molecular dynamics simulation. MCAD and FMN-bp form a tetramer and dimer, respectively. The CS and CR rates of an individual donor and various related physical quantities were numerically obtained. It was found that both CS and CR rates were fastest from Trp166 among four Trps in MCAD and those from Trp106 among two Trps in FMN-bp. Logarithmic CS rates in MCAD were dependent on the donor-acceptor distance (Rc) with parabolic functions, while those of CR rates linearly decreased with Rc. Reasons why CS rates were faster than CR rates in both MCAD and FMN-bp were elucidated in terms of pre-exponential factors in the theory. The present method could be useful to understand the precise mechanisms of initial steps of biological functions of photoreceptors in plants.