Excitonic coupling effect on the circular dichroism spectrum of sodium-pumping rhodopsin KR2
Excitonic coupling effect on the circular dichroism spectrum of sodium-pumping rhodopsin KR2
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DOI：
10.1063/5.0013642
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发表时间：
2020-07-28
影响因子：
4.4
通讯作者：
Inoue, Keiichi
中科院分区：
文献类型：
--
作者：
Fujimoto, Kazuhiro J.;Inoue, Keiichi
我们利用结合过渡密度片段相互作用（TDFI）方法的激子模型研究了Krokinobacter eikastus rhodopsin 2 （KR2）视网膜发色团之间的激子耦合在圆二色（CD）光谱中的作用。虽然视网膜蛋白的多次形成通常会诱导双相的阴性和阳性CD带，但KR2五聚体只显示一条阳性CD带。TDFI计算揭示了库仑相互作用对激子耦合能的主要贡献，交换和电荷转移相互作用对激子耦合能的贡献可以忽略不计。用TDFI建立的激子模型成功地再现了KR2的实验吸收和CD光谱的主要特征，这使我们能够研究KR2五聚体中CD光谱形状的机理。结果清楚地表明，CD波段的红移归因于视网膜发色团之间的激子耦合。进一步分析表明，弱激子耦合对CD谱的形状起着至关重要的作用。该方法为了解KR2 CD光谱的起源提供了基础，并有助于分析生物系统中发色团-发色团相互作用的机制。由AIP出版社授权出版。
We investigate the role of excitonic coupling between retinal chromophores of Krokinobacter eikastus rhodopsin 2 (KR2) in the circular dichroism (CD) spectrum using an exciton model combined with the transition density fragment interaction (TDFI) method. Although the multimer formation of retinal protein commonly induces biphasic negative and positive CD bands, the KR2 pentamer shows only a single positive CD band. The TDFI calculation reveals the dominant contribution of the Coulomb interaction and negligible contributions of exchange and charge-transfer interactions to the excitonic coupling energy. The exciton model with TDFI successfully reproduces the main features of the experimental absorption and CD spectra of KR2, which allow us to investigate the mechanism of the CD spectral shape observed in the KR2 pentamer. The results clearly show that the red shift of the CD band is attributed to the excitonic coupling between retinal chromophores. Further analysis reveals that the weak excitonic coupling plays a crucial role in the shape of the CD spectrum. The present approach provides a basis for understanding the origin of the KR2 CD spectrum and is useful for analyzing the mechanism of chromophore-chromophore interactions in biological systems. Published under license by AIP Publishing.