Retinal Conformation and Dynamics in Activation of Rhodopsin Illuminated by Solid-state 2H NMR Spectroscopy
Retinal Conformation and Dynamics in Activation of Rhodopsin Illuminated by Solid-state 2H NMR Spectroscopy
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DOI：
10.1111/j.1751-1097.2008.00510.x
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发表时间：
2009-03-01
影响因子：
3.3
通讯作者：
Struts, Andrey V.
中科院分区：
文献类型：
--
作者：
Brown, Michael F.;Martinez-Mayorga, Karina;Struts, Andrey V.
固态核磁共振光谱学提供了一个强大的途径，研究G蛋白偶联受体和其他不可分割的膜蛋白在一个类似天然的环境。本文综述了利用固体H-2NMR研究视紫红质在暗态下的视网膜辅因子以及Meta I和Meta II光中间体。位点特异性的H-2 NMR标记已被引入到三个区域（甲基）的视网膜是至关重要的光化学功能的视紫红质。尽管其惊人的稳定性H-2 NMR光谱表明，视网膜内的蛋白质结合腔经历快速波动。光谱线形揭示了甲基快速自旋围绕其三重（C-3）轴与序参数为S-C3的离轴运动近似为0.9。对于暗态，11-顺式-视黄醛的H-2 NMR结构表明由于配体和蛋白质的空间相互作用，多烯链和β-紫罗酮环都发生了扭转。视网膜被容纳在视紫红质结合袋内，具有关于C11 = C12双键的负预扭曲。构象畸变解释了其快速的光化学反应，并揭示了11-顺式到反式异构化的轨迹。此外，H-2NMR已被应用于研究在黑暗和光激活状态下的视黄叉基动力学。异构化后，所有三个甲基的迁移率都发生了剧烈的变化。弛豫数据支持一种激活机制，由此视黄醇的β-紫罗酮环保持在几乎相同的环境中，而没有配体的大位移。β-紫罗酮环和亚视黄基席夫碱与蛋白质的相互作用传递了视黄异构化的力。因此，固态H-2 NMR提供了有关能量流动的信息，这些能量流动触发了感光体激活机制中氢键网络和螺旋运动的变化。
Solid-state NMR spectroscopy gives a powerful avenue for investigating G protein-coupled receptors and other integral membrane proteins in a native-like environment. This article reviews the use of solid-state H-2 NMR to study the retinal cofactor of rhodopsin in the dark state as well as the meta I and meta II photointermediates. Site-specific H-2 NMR labels have been introduced into three regions (methyl groups) of retinal that are crucially important for the photochemical function of rhodopsin. Despite its phenomenal stability H-2 NMR spectroscopy indicates retinal undergoes rapid fluctuations within the protein binding cavity. The spectral lineshapes reveal the methyl groups spin rapidly about their three-fold (C-3) axes with an order parameter for the off-axial motion of S-C3 approximate to 0.9. For the dark state, the H-2 NMR structure of 11-cis-retinal manifests torsional twisting of both the polyene chain and the beta-ionone ring due to steric interactions of the ligand and the protein. Retinal is accommodated within the rhodopsin binding pocket with a negative pretwist about the C11 = C12 double bond. Conformational distortion explains its rapid photochemistry and reveals the trajectory of the 11-cis to trans isomerization. In addition, H-2 NMR has been applied to study the retinylidene dynamics in the dark and light-activated states. Upon isomerization there are drastic changes in the mobility of all three methyl groups. The relaxation data support an activation mechanism whereby the beta-ionone ring of retinal stays in nearly the same environment, without a large displacement of the ligand. Interactions of the beta-ionone ring and the retinylidene Schiff base with the protein transmit the force of the retinal isomerization. Solid-state H-2 NMR thus provides information about the flow of energy that triggers changes in hydrogen-bonding networks and helix movements in the activation mechanism of the photoreceptor.