Many organisms sense light using rhodopsins, photoreceptive proteins containing a retinal chromophore. Here we report the discovery, structure and biophysical characterization of bestrhodopsins, a microbial rhodopsin subfamily from marine unicellular algae, in which one rhodopsin domain of eight transmembrane helices or, more often, two such domains in tandem, are C-terminally fused to a bestrophin channel. Cryo-EM analysis of a rhodopsin-rhodopsin-bestrophin fusion revealed that it forms a pentameric megacomplex (~700 kDa) with five rhodopsin pseudodimers surrounding the channel in the center. Bestrhodopsins are metastable and undergo photoconversion between red- and green-absorbing or green- and UVA-absorbing forms in the different variants. The retinal chromophore, in a unique binding pocket, photoisomerizes from all-trans to 11-cis form. Heterologously expressed bestrhodopsin behaves as a light-modulated anion channel.

许多生物体使用视紫红质来感知光，视紫红质是一种含有视网膜发色团的感光蛋白。在这里，我们报告了 bestrhodopsins 的发现、结构和生物物理特性，这是一种来自海洋单细胞藻类的微生物视紫红质亚家族，其中八个跨膜螺旋的一个视紫红质结构域，或者更常见的是两个这样的串联结构域，在 C 端与 bestrophin 融合渠道。对视紫红质-视紫红质-bestrophin 融合物的冷冻电镜分析显示，它形成了一个五聚体巨型复合物（~700 kDa），中心通道周围有五个视紫红质假二聚体。视紫红质是亚稳态的，并且在不同变体中经历红色和绿色吸收或绿色和 UVA 吸收形式之间的光转换。视网膜发色团，在一个独特的结合口袋里，从所有的光异构化反式到 11-顺式形式。异源表达的视紫红质表现为光调制阴离子通道。