The Magnitude of the Light-induced Conformational Change in Different Rhodopsins Correlates with Their Ability to Activate G Proteins
The Magnitude of the Light-induced Conformational Change in Different Rhodopsins Correlates with Their Ability to Activate G Proteins
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DOI：
10.1074/jbc.m109.016212
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发表时间：
2009-07-31
影响因子：
4.8
通讯作者：
Terakita, Akihisa
中科院分区：
文献类型：
--
作者：
Tsukamoto, Hisao;Farrens, David L.;Terakita, Akihisa
光将视紫红质（原型G蛋白偶联受体）转化为能够激活G蛋白的形式。最近的研究表明，不同的视紫红质在光激活状态下具有不同的分子特性，特别是激活G蛋白的能力不同。例如，牛视紫红质在激活G蛋白方面比对视紫红质（一种非视觉视紫红质）有效20倍，尽管这些视紫红质具有相对高的序列相似性。在这里，我们已经调查了可能导致这种差异的结构方面。使用定点荧光标记方法，我们将荧光探针bimane连接到两种视紫红质中跨膜螺旋V和VI的胞质末端中引入的半胱氨酸残基。这些探针的荧光光谱，以及它们的可及性水淬灭剂在牛视紫红质的光活化后显着改变，但只有适度的parapinopsin。我们还比较了螺旋V和VI的相对运动时，通过引入bimane标签和bimane淬灭残基色氨酸到螺旋VI和V，分别光活化的视紫红质。这两种受体在激活后显示在该区域的运动，虽然运动似乎更大的牛视紫红质比parainopsin。总之，这些数据表明，牛视紫红质的螺旋V和VI中的较大构象变化解释了为什么它比其他视紫红质具有更大的G蛋白活化能力。螺旋运动的不同幅度也可能是G蛋白偶联受体功能多样性的原因。
Light converts rhodopsin, the prototypical G protein-coupled receptor, into a form capable of activating G proteins. Recent work has shown that the light-activated state of different rhodopsins can possess different molecular properties, especially different abilities to activate G protein. For example, bovine rhodopsin is similar to 20-fold more effective at activating G protein than parapinopsin, a non-visual rhodopsin, although these rhodopsins share relatively high sequence similarity. Here we have investigated possible structural aspects that might underlie this difference. Using a site-directed fluorescence labeling approach, we attached the fluorescent probe bimane to cysteine residues introduced in the cytoplasmic ends of transmembrane helices V and VI in both rhodopsins. The fluorescence spectra of these probes as well as their accessibility to aqueous quenching agents changed dramatically upon photoactivation in bovine rhodopsin but only moderately so in parapinopsin. We also compared the relative movement of helices V and VI upon photoactivation of both rhodopsins by introducing a bimane label and the bimane-quenching residue tryptophan into helices VI and V, respectively. Both receptors showed movement in this region upon activation, although the movement appears much greater in bovine rhodopsin than in parapinopsin. Together, these data suggest that a larger conformational change in helices V and VI of bovine rhodopsin explains why it has greater G protein activation ability than other rhodopsins. The different amplitude of the helix movement may also be responsible for functional diversity of G protein-coupled receptors.