Covalent Bond between Ligand and Receptor Required for Efficient Activation in Rhodopsin
Covalent Bond between Ligand and Receptor Required for Efficient Activation in Rhodopsin
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DOI：
10.1074/jbc.m109.063875
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发表时间：
2010-03-12
影响因子：
4.8
通讯作者：
Shichida, Yoshinori
中科院分区：
文献类型：
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作者：
Matsuyama, Take;Yamashita, Takahiro;Shichida, Yoshinori
视紫红质是一个被广泛研究的g蛋白偶联受体（gpcr）成员。虽然视紫红质与其他gpcr具有许多共同的特征，但它作为光感受器分子具有独特的特征。视紫红质分子结构的一个标志是共价结合的发色团，它调节受体作为激动剂或反激动剂的活性。本研究利用视黄醛希夫碱基重组的视紫红质突变体K296G，揭示了视网膜发色团与296位赖氨酸残基之间的共价键在牛视紫红质激活途径中的关键作用。我们的研究结果表明，视紫质的光感受功能，如配体的区域特异性光异构化及其量子产率不受共价键缺失的影响，但视网膜光异构化引发的激活机制受到严重影响。此外，我们的研究结果表明，该突变体在漂白过程中没有形成与野生型视紫质的Meta-II中间体相似的活性状态，尽管由于受体的基础活性增加，其在光照后表现出相对较弱的G蛋白活性。我们认为，共价键是将光异构化的激动剂传递到受体的结构变化所必需的，并且共价键将低亲和力的激动剂强制保留在受体中，从而导致更有效的G蛋白激活。
Rhodopsin is an extensively studied member of the G-protein coupled receptors (GPCRs). Although rhodopsin shares many features with the other GPCRs, it exhibits unique features as a photoreceptor molecule. A hallmark in the molecular structure of rhodopsin is the covalently bound chromophore that regulates the activity of the receptor acting as an agonist or inverse agonist. Here we show the pivotal role of the covalent bond between the retinal chromophore and the lysine residue at position 296 in the activation pathway of bovine rhodopsin, by use of a rhodopsin mutant K296G reconstituted with retinylidene Schiff bases. Our results show that photoreceptive functions of rhodopsin, such as regiospecific photoisomerization of the ligand, and its quantum yield were not affected by the absence of the covalent bond, whereas the activation mechanism triggered by photoisomerization of the retinal was severely affected. Furthermore, our results show that an active state similar to the Meta-II intermediate of wild-type rhodopsin did not form in the bleaching process of this mutant, although it exhibited relatively weak G protein activity after light irradiation because of an increased basal activity of the receptor. We propose that the covalent bond is required for transmitting structural changes from the photoisomerized agonist to the receptor and that the covalent bond forcibly keeps the low affinity agonist in the receptor, resulting in a more efficient G protein activation.