Electrostatics guide chromophore twist Photoisomerization—the twisting of bonds in a molecule in response to absorption of light—is exploited in biology to sense light and can influence the photophysical properties of fluorescent proteins used in imaging applications. Romei et al. studied this behavior by introducing unnatural amino acids into the photoswitchable green fluorescent protein Dronpa2, thus systematically altering the electronic properties of the chromophore (see the Perspective by Hu et al.). Crystal structures and spectroscopic analyses of a series of these variants support a model in which the electrostatic interactions between the chromophore and its environment influence the barrier heights for twisting around different bonds during photoisomerization. These insights may guide future design of photoswitchable proteins with desired properties. Science, this issue p. 76; see also p. 26 Chromophore charge-transfer character and protein electrostatics bias photoisomerization pathways. Rotation around a specific bond after photoexcitation is central to vision and emerging opportunities in optogenetics, super-resolution microscopy, and photoactive molecular devices. Competing roles for steric and electrostatic effects that govern bond-specific photoisomerization have been widely discussed, the latter originating from chromophore charge transfer upon excitation. We systematically altered the electrostatic properties of the green fluorescent protein chromophore in a photoswitchable variant, Dronpa2, using amber suppression to introduce electron-donating and electron-withdrawing groups to the phenolate ring. Through analysis of the absorption (color), fluorescence quantum yield, and energy barriers to ground- and excited-state isomerization, we evaluate the contributions of sterics and electrostatics quantitatively and demonstrate how electrostatic effects bias the pathway of chromophore photoisomerization, leading to a generalized framework to guide protein design.

中文翻译：

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蛋白质光异构化途径的静电控制

静电引导发色团扭曲 光异构化——分子中的键响应于光的吸收而扭曲——在生物学中被利用来感知光，并且可以影响成像应用中使用的荧光蛋白的光物理特性。罗梅等人。通过将非天然氨基酸引入可光控绿色荧光蛋白 Dronpa2 来研究这种行为，从而系统地改变生色团的电子特性（参见 Hu 等人的观点）。一系列这些变体的晶体结构和光谱分析支持一个模型，其中发色团与其环境之间的静电相互作用会影响光异构化过程中围绕不同键扭曲的势垒高度。这些见解可能会指导具有所需特性的光开关蛋白质的未来设计。科学，这个问题 p。76; 另见第。26 发色团电荷转移特性和蛋白质静电偏置光异构化途径。光激发后围绕特定键的旋转是视觉和光遗传学、超分辨率显微镜和光敏分子器件中出现的机会的核心。控制特定键的光异构化的空间和静电效应的竞争作用已被广泛讨论，后者源自激发时的生色团电荷转移。我们系统地改变了光开关变体 Dronpa2 中绿色荧光蛋白发色团的静电特性，使用琥珀抑制将给电子和吸电子基团引入苯酚环。通过对基态和激发态异构化的吸收（颜色）、荧光量子产率和能量势垒的分析，我们定量评估了空间和静电的贡献，并证明了静电效应如何偏置发色团光异构化的途径，从而得到一个广义的指导蛋白质设计的框架。