PDF(Pubmed)
Abstract：
Discovered over 50 years ago, bacteriorhodopsin is the first recognized and most widely studied microbial retinal protein. Serving as a light-activated proton pump, it represents the archetypal ion-pumping system. Here we compare the photochemical dynamics of bacteriorhodopsin light and dark-adapted forms with that of the first metastable photocycle intermediate known as \"K\". We observe that following thermal double isomerization of retinal in the dark from bio-active all-trans 15-anti to 13-cis, 15-syn, photochemistry proceeds even faster than the ~0.5 ps decay of the former, exhibiting ballistic wave packet curve crossing to the ground state. In contrast, photoexcitation of K containing a 13-cis, 15-anti chromophore leads to markedly multi-exponential excited state decay including much slower stages. QM/MM calculations, aimed to interpret these results, highlight the crucial role of protonation, showing that the classic quadrupole counterion model poorly reproduces spectral data and dynamics. Single protonation of ASP212 rectifies discrepancies and predicts triple ground state structural heterogeneity aligning with experimental observations. These findings prompt a reevaluation of counter ion protonation in bacteriorhodopsin and contribute to the broader understanding of its photochemical dynamics.
摘要：
发现于50多年前,细菌视紫红质是第一个公认和研究最广泛的微生物视网膜蛋白。用作光激活质子泵，它代表了典型的离子抽运系统。在这里，我们比较了细菌视紫红质光和暗适应形式的光化学动力学与第一个亚稳态光循环中间体“K”的光化学动力学。我们观察到，在黑暗中视黄醛从生物活性全反式15-抗到13-顺式的热双异构化之后，15-syn,光化学的进展甚至比前者的~0.5ps衰减更快，表现出与基态相交的弹道波包曲线。相比之下,包含13-cis的K的光激发，15-反发色团导致明显的多指数激发态衰减，包括慢得多的阶段。QM/MM计算，为了解释这些结果，强调质子化的关键作用，表明经典的四极反离子模型再现光谱数据和动力学效果不佳。ASP212的单质子化纠正了差异，并根据实验观察结果预测了三重基态结构异质性。这些发现促使人们重新评估细菌视紫红质中的反离子质子化作用，并有助于对其光化学动力学的更广泛理解。
