A Microbial Rhodopsin with a Unique Retinal Composition Shows Both Sensory Rhodopsin II and Bacteriorhodopsin-like Properties
A Microbial Rhodopsin with a Unique Retinal Composition Shows Both Sensory Rhodopsin II and Bacteriorhodopsin-like Properties
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DOI：
10.1074/jbc.m110.190058
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发表时间：
2011-02-25
影响因子：
4.8
通讯作者：
Homma, Michio
中科院分区：
文献类型：
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作者：
Sudo, Yuki;Ihara, Kunio;Homma, Michio
视紫红质具有由7个跨膜α -螺旋包围的视网膜发色团，广泛存在于原核生物和真核生物中，可作为光遗传工具。虽然视紫红质在各种生物中作为不同的光感受器发挥着明显不同的作用，但根据其光能转换和光信号转导这两个基本功能，视紫红质可以进行大致的划分。在微生物中，作为光能转换器的光驱动质子转运体在进化过程中被修改，以产生感觉受体，将信号传递给换能器蛋白以控制运动。在这项研究中，我们克隆并鉴定了两种新发现的微生物紫红质。其中一种具有光化学性质和质子泵活性，类似于众所周知的质子泵细菌视紫红质（BR）。另一种称为中视紫红质（MR），是介于BR和感光感觉视紫红质II （SRII）之间的进化过渡体，具有SRII样的最大吸收，BR样的光循环和独特的视网膜成分。野生型核磁共振不具有光诱导质子泵活动。另一方面，具有两个关键氢键残基的突变体MR与换能器蛋白HtrII的相互作用表面显示出与SRII相似的强大的趋光性反应，表明MR可能具有信号传导能力。这些结果表明，色调和关键苏氨酸残基的插入在感觉视紫红质进化的早期就发生了。MR可能是1型紫红质（微生物）向2型紫红质（动物）进化过程中缺失的一环，因为它是已知的第一个具有与2型紫红质相似的11-顺式视网膜的微生物紫红质。
Rhodopsins possess retinal chromophore surrounded by seven transmembrane alpha-helices, are widespread in prokaryotes and in eukaryotes, and can be utilized as optogenetic tools. Although rhodopsins work as distinctly different photo-receptors in various organisms, they can be roughly divided according to their two basic functions, light-energy conversion and light-signal transduction. In microbes, light-driven proton transporters functioning as light-energy converters have been modified by evolution to produce sensory receptors that relay signals to transducer proteins to control motility. In this study, we cloned and characterized two newly identified microbial rhodopsins from Haloquadratum walsbyi. One of them has photochemical properties and a proton pumping activity similar to the well known proton pump bacteriorhodopsin (BR). The other, named middle rhodopsin (MR), is evolutionarily transitional between BR and the phototactic sensory rhodopsin II (SRII), having an SRII-like absorption maximum, a BR-like photocycle, and a unique retinal composition. The wild-type MR does not have a light-induced proton pumping activity. On the other hand, a mutant MR with two key hydrogen-bonding residues located at the interaction surface with the transducer protein HtrII shows robust phototaxis responses similar to SRII, indicating that MR is potentially capable of the signaling. These results demonstrate that color tuning and insertion of the critical threonine residue occurred early in the evolution of sensory rhodopsins. MR may be a missing link in the evolution from type 1 rhodopsins (microorganisms) to type 2 rhodopsins (animals), because it is the first microbial rhodopsin known to have 11-cis-retinal similar to type 2 rhodopsins.