Electrostatic Control of the Photoisomerization Efficiency and Optical Properties in Visual Pigments: On the Role of Counterion Quenching
Electrostatic Control of the Photoisomerization Efficiency and Optical Properties in Visual Pigments: On the Role of Counterion Quenching
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DOI：
10.1021/ja808424b
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发表时间：
2009-04-15
影响因子：
15
通讯作者：
Garavelli, Marco
中科院分区：
文献类型：
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作者：
Tomasello, Gaia;Olaso-Gonzalez, Gloria;Garavelli, Marco
混合QM（CASPT 2//CASSCF/6- 31 G *）/MM（Amber）计算已用于绘制视紫红质中视网膜发色团的光异构化路径，并探索视色素中光敏效率和光谱控制背后的原因。结果表明，虽然静电环境中起着核心作用，在适当调整的生色团的光学性质，它也是关键的偏置的超快光化学事件：它控制的光异构化通道的斜率以及S-1/S-0交叉空间触发超快衰减的可访问性。明确分析了E113 counterweight，E181残基和蛋白质口袋的其他氨基酸的作用：看来，counterweight淬灭蛋白质环境中起着关键作用，在建立发色团的光学性质和其光化学效率。提出了一个统一的方案，揭示了在视紫红质的光谱和机械性能之间的关系，并允许我们绘制一个坚实的机制，在色觉色素的光谱调谐：一个可调的countershielding出现作为选修机制的LM光谱调制，而视网膜的构象控制必须支配S吸收。最后，有人建议，这种模式可能有助于揭示新的光突变相关的视觉缺陷，在这一领域的实验生物分子研究开辟了创新的前景。
Hybrid QM(CASPT2//CASSCF/6-31G*)/MM(Amber) computations have been used to map the photoisomerization path of the retinal chromophore in Rhodopsin and explore the reasons behind the photoactivity efficiency and spectral control in the visual pigments. It is shown that while the electrostatic environment plays a central role in properly tuning the optical properties of the chromophore, it is also critical in biasing the ultrafast photochemical event: it controls the slope of the photoisomerization channel as well as the accessibility of the S-1/S-0 crossing space triggering the ultrafast decay. The roles of the El 13 counterion, the E181 residue, and the other amino acids of the protein pocket are explicitly analyzed: it appears that counterion quenching by the protein environment plays a key role in setting up the chromophore's optical properties and its photochemical efficiency. A unified scenario is presented that discloses the relationship between spectroscopic and mechanistic properties in rhodopsins and allows us to draw a solid mechanism for spectral tuning in color vision pigments: a tunable counterion shielding appears as the elective mechanism for L M spectral modulation, while a retinal conformational control must dictate S absorption. Finally, it is suggested that this model may contribute to shed new light into mutations-related vision deficiencies that opens innovative perspectives for experimental biomolecular investigations in this field.