Chromophore Structure in an Inactive State of a Novel Photosensor Protein Opn5L1: Resonance Raman Evidence for the Formation of a Deprotonated Adduct at the 11th Carbon Atom
Chromophore Structure in an Inactive State of a Novel Photosensor Protein Opn5L1: Resonance Raman Evidence for the Formation of a Deprotonated Adduct at the 11th Carbon Atom
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新型光电传感器蛋白 Opn5L1 非活性状态下的发色团结构：第 11 个碳原子处形成去质子化加合物的共振拉曼证据
DOI：
10.1021/acs.jpcb.2c08780
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
and Yasuhisa Mizutani
中科院分区：
文献类型：
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作者：
Misao Mizuno;Keita Sato;Takahiro Yamashita;Kazumi Sakai;Yasushi Imamoto;Yumiko Yamano;Akimori Wada;Hideyo Ohuchi;Yoshinori Shichida;and Yasuhisa Mizutani
视蛋白是光敏G蛋白偶联受体蛋白，分为视觉和非视觉受体。Opn5L1是一种非视觉视蛋白，作为发色团结合全transretinal。Opn5L1的一个独特特征是蛋白质在光激发时表现出光环化反应。确定光循环中中间体的发色团结构对于理解Opn5L1的功能机制至关重要。先前的一项研究表明，光循环中的长寿命中间体不能激活G蛋白，并在视网膜发色团和附近的半胱氨酸残基之间形成共价键。然而，这个共价键在发色团中的位置仍然不确定。在这里，我们报告的同位素标记的样品的共振拉曼研究结合密度泛函理论计算，并揭示，第11个碳原子的发色团的中间体形成共价键的半胱氨酸残基。此外，基于同位素取代和密度泛函理论计算的振动归属表明，中间体的席夫碱是去质子化的。在本研究中确定的发色团结构很好地解释了光环化反应的机制，这是至关重要的光生物功能的Opn5L1。
Opsins are photosensitive G protein-coupled receptor proteins and are classified into visual and nonvisual receptors. Opn5L1 is a nonvisual opsin that binds all-transretinal as a chromophore. A unique feature of Opn5L1 is that the protein exhibits a photocyclic reaction upon photoexcitation. Determining the chromophore structures of intermediates in the photocycle is essential for understanding the functional mechanism of Opn5L1. A previous study revealed that a long-lived intermediate in the photocycle cannot activate the G protein and forms a covalent bond between the retinal chromophore and a nearby cysteine residue. However, the position of this covalent bond in the chromophore remains undetermined. Here, we report a resonance Raman study on isotopically labeled samples in combination with density functional theory calculations and reveal that the 11th carbon atom of the chromophore of the intermediate forms a covalent linkage to the cysteine residue. Furthermore, vibrational assignments based on the isotopic substitutions and density functional theory calculations suggested that the Schiff base of the intermediate is deprotonated. The chromophore structure determined in the present study well explains the mechanism of the photocyclic reaction, which is crucial to the photobiological function of Opn5L1.