Photocyclic behavior of rhodopsin induced by an atypical isomerization mechanism
Photocyclic behavior of rhodopsin induced by an atypical isomerization mechanism
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DOI：
10.1073/pnas.1617446114
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发表时间：
2017-03-28
影响因子：
11.1
通讯作者：
Palczewski, Krzysztof
中科院分区：
文献类型：
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作者：
Gulati, Sahil;Jastrzebska, Beata;Palczewski, Krzysztof
脊椎动物视紫红质 (Rh) 含有 11-顺式视黄醛作为发色团，可将光能转化为视觉信号。吸收光后，11-顺式视黄醛异构化为全反式视黄醛，构成一种单向反应，激活转导蛋白 (G(t))，随后释放发色团。在这里，我们报道了牛Rh，用六碳环视网膜发色团再生，该发色团具有锁定在其顺式构象的C-11 = C-12双键（Rh6mr），采用非典型异构化机制，将11-顺式转化为11,13-二顺式构型，以延长G（t）激活时间。时间依赖性紫外可见光谱、高效液相色谱和分子力学分析揭示了 11,13-二顺式构型在较慢的时间尺度上发生非典型热重异构化，这使得 Rh6mr 能够以类似于微生物 Rhs 的光循环方式发挥作用。凭借这种光循环行为，Rh6mr 反复招募并激活 Gt 以响应光刺激，使其成为基于视网膜类似物结合脊椎动物 Rhs 的光遗传学工具的绝佳候选者。总体而言，这些全面的结构功能研究揭示了通过 11-cis-to-11,13-dicis 异构化激活 Rh 的独特光循环机制。
Vertebrate rhodopsin (Rh) contains 11-cis-retinal as a chromophore to convert light energy into visual signals. On absorption of light, 11-cis-retinal is isomerized to all-trans-retinal, constituting a one-way reaction that activates transducin (G(t)) followed by chromophore release. Here we report that bovine Rh, regenerated instead with a six-carbon-ring retinal chromophore featuring a C-11=C-12 double bond locked in its cis conformation (Rh6mr), employs an atypical isomerization mechanism by converting 11-cis to an 11,13-dicis configuration for prolonged G(t) activation. Time-dependent UV-vis spectroscopy, HPLC, and molecular mechanics analyses revealed an atypical thermal reisomerization of the 11,13-dicis to the 11-cis configuration on a slow timescale, which enables Rh6mr to function in a photocyclic manner similar to that of microbial Rhs. With this photocyclic behavior, Rh6mr repeatedly recruits and activates Gt in response to light stimuli, making it an excellent candidate for optogenetic tools based on retinal analog-bound vertebrate Rhs. Overall, these comprehensive structure-function studies unveil a unique photocyclic mechanism of Rh activation by an 11-cis-to-11,13-dicis isomerization.