瞬态二维红外光谱与多尺度模拟揭示蓝细菌光敏色素Slr1393-g3中的振动耦合
Transient 2D IR spectroscopy and multiscale simulations reveal vibrational couplings in the Cyanobacteriochrome Slr1393-g3
AI总结：
本文利用瞬态红外和二维红外光谱结合QM/MM多尺度模拟，揭示了蓝细菌光敏色素Slr1393-g3光循环中的新中间体及振动耦合机制。
摘要：
蓝细菌光敏色素是一类双稳态光受体蛋白，具有适用于光遗传学或荧光显微镜等生物技术应用的优良光化学性质。本文研究了Slr1393-g3，一种可在红光吸收型（Pr）和绿光吸收型（Pg）之间可逆光切换的蓝细菌光敏色素。我们应用先进的红外光谱方法，在跨越多个时间数量级的尺度上追踪光循环过程中间体的序列。在从Pg到Pr的转化过程中，我们利用瞬态红外光谱揭示了一个先于Pr形成的新中间体。此外，稳态和瞬态二维红外实验测量了这些中间态期间发色团不同基团与蛋白质之间的振动耦合。非谐量子力学/分子力学（QM/MM）计算预测的光谱与光循环初始态和终态的二维红外实验光谱在接近定量的水平上一致。这些计算有助于红外光谱的指认，并提供了对耦合机制的原子级认识。这为光谱结果的解释奠定了基础，并提示了中间体沿光循环的结构变化。
英文摘要：
Cyanobacteriochromes are bi-stable photoreceptor proteins with desirable photochemical properties for biotechnological applications such as optogenetics or fluorescence microscopy. Here, we investigated Slr1393-g3, a cyanobacteriochrome that reversibly photo-switches between a red-absorbing (Pr) and green-absorbing (Pg) form. We applied advanced IR spectroscopic methods to track the sequence of intermediates during the photocycle over many orders in magnitude in time. In the conversion from Pg to Pr, we have revealed a new intermediate which precedes the Pr formation by using transient IR spectroscopy. In addition, stationary and transient 2D~IR experiments measured the vibrational couplings between different groups of the chromophore and the protein during these intermediate states. Anharmonic QM/MM calculations predict spectra in close-to-quantitative agreement with experimental 2D~IR spectra of the initial and the final state of the photocycle. They facilitate the assignment of the IR spectra and provide an atomistic insight into the coupling mechanism. This serves as a basis for the interpretation of the spectroscopic results and suggests structural changes of the intermediates along the photocycle.
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