Directional transport of protons across an energy transducing membrane-proton pumping-is ubiquitous in biology. Bacteriorhodopsin (bR) is a light-driven proton pump that is activated by a buried all-trans retinal chromophore being photoisomerized to a 13-cis conformation. The mechanism by which photoisomerization initiates directional proton transport against a proton concentration gradient has been studied by a myriad of biochemical, biophysical, and structural techniques. X-ray free electron lasers (XFELs) have created new opportunities to probe the structural dynamics of bR at room temperature on timescales from femtoseconds to milliseconds using time-resolved serial femtosecond crystallography (TR-SFX). Wereview these recent developments and highlight where XFEL studies reveal new details concerning the structural mechanism of retinal photoisomerization and proton pumping. We also discuss the extent to which these insights were anticipated by earlier intermediate trapping studies using synchrotron radiation. TR-SFX will open up the field for dynamical studies of other proteins that are not naturally light-sensitive.

中文翻译：

---

细菌视紫红质：使用X射线激光和同步辐射显示的结构见解。

跨能量转换膜-质子泵送的质子定向运输在生物学中无处不在。细菌视紫红质（bR）是一种光驱动的质子泵，其由被掩埋的全反式视网膜发色团激活，并被光异构化为13-顺式构象。已经通过多种生化，生物物理和结构技术研究了光致异构化引发质子对质子浓度梯度的定向质子运输的机理。X射线自由电子激光器（XFEL）创造了新的机会，可以使用时间分辨的串联飞秒晶体学（TR-SFX）在室温下从飞秒到毫秒的时间范围内探测bR的结构动力学。我们回顾了这些最新进展，并重点介绍了XFEL研究在何处揭示了有关视网膜光异构化和质子泵浦的结构机理的新细节。我们还将讨论使用同步加速器辐射进行的较早的中间捕获研究对这些见解的预期程度。TR-SFX将为动态研究非天然光敏感的其他蛋白质开辟领域。