Faculty of Biology, M.V. Lomonosov Moscow State University, Moscow, Russia.
A.N. Bach Institute of Biochemistry, Federal Research Center of Biotechnology of the Russian Academy of Sciences, Moscow, Russia.
Commun Biol. 2021 May 10;4(1):539. doi: 10.1038/s42003-021-02022-3.
Here, we propose a possible photoactivation mechanism of a 35-kDa blue light-triggered photoreceptor, the Orange Carotenoid Protein (OCP), suggesting that the reaction involves the transient formation of a protonated ketocarotenoid (oxocarbenium cation) state. Taking advantage of engineering an OCP variant carrying the Y201W mutation, which shows superior spectroscopic and structural properties, it is shown that the presence of Trp201 augments the impact of one critical H-bond between the ketocarotenoid and the protein. This confers an unprecedented homogeneity of the dark-adapted OCP state and substantially increases the yield of the excited photoproduct S*, which is important for the productive photocycle to proceed. A 1.37 Å crystal structure of OCP Y201W combined with femtosecond time-resolved absorption spectroscopy, kinetic analysis, and deconvolution of the spectral intermediates, as well as extensive quantum chemical calculations incorporating the effect of the local electric field, highlighted the role of charge-transfer states during OCP photoconversion.
在这里，我们提出了一种 35kDa 蓝光触发光受体——橙色类胡萝卜素蛋白 (OCP) 的可能光激活机制，表明该反应涉及到质子化酮类胡萝卜素（氧碳正离子）态的瞬时形成。利用工程改造携带 Y201W 突变的 OCP 变体，该变体显示出优越的光谱和结构特性，表明色氨酸 201 的存在增强了酮类胡萝卜素和蛋白质之间一个关键氢键的影响。这赋予了暗适应 OCP 状态前所未有的均一性，并大大提高了激发光产物 S*的产率，这对于进行有生产力的光循环很重要。OCP Y201W 的 1.37Å 晶体结构结合飞秒时间分辨吸收光谱、动力学分析和光谱中间体的解卷积，以及包含局部电场效应的广泛量子化学计算，突出了电荷转移态在 OCP 光转化过程中的作用。
