Transient Resonance Raman Spectroscopy of a Light-Driven Sodium-Ion-Pump Rhodopsin from Indibacter alkaliphilus
Transient Resonance Raman Spectroscopy of a Light-Driven Sodium-Ion-Pump Rhodopsin from Indibacter alkaliphilus
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DOI：
10.1021/acs.jpcb.7b02421
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发表时间：
2017-05-04
影响因子：
3.3
通讯作者：
Unno, Masashi
中科院分区：
文献类型：
--
作者：
Kajimoto, Kousuke;Kikukawa, Takashi;Unno, Masashi
钠离子泵视紫红质（NaR）是一种在光循环过程中转运Na+的微生物视紫红质。本文利用瞬态吸收光谱和瞬态共振拉曼光谱研究了嗜碱Indibacter alkaliphilus中NaR的光循环机理。瞬态吸收数据表明，NaR的光循环为K（545 nm）→ L（490 nm）/M（420 mu）O-1（590 nm）O-2（56 Q mu）NaR，其中L和M形成平衡态.通过442和532 nm激发的共振拉曼光谱证实了K、L、M和O中间体的存在。瞬态共振拉曼光谱的主要成分是由于L含有1 '3-顺式视黄醇质子化席夫碱。增强的氢平面外带的存在，以及其对H/D交换的敏感性表明，在L中的席夫碱区域附近的视网膜发色团是扭曲的。此外，L态的视黄酸席夫碱形成的氢键比暗态的强。这些观察结果是一致的Na+泵机制，涉及质子转移从视网膜席夫碱的一个关键的天冬氨酸残基（Asp 116在Krokinaseikastus视紫红质2）在L/M状态。
Sodium-ion-pump rhodopsin (NaR) is a microbial rhodopsin that transports Na+ during its photocycle. Here we explore the photocycle mechanism of NaR from Indibacter alkaliphilus with transient absorption and transient resonance Raman spectroscopy. The transient absorption data indicate that the photocycle of NaR is K (545 nm) -> L (490 nm)/M (420 mu) O-1 (590 rim) O-2 (56Q mu) NaR, where the L and M are formed as equilibrium states. The presence of K, L, M, and O intermediates was confirmed by the resonance Raman spectra with 442 and 532 nm excitation. The main component of the transient resonance Raman spectra was due to L which contains a 1'3 -cis retinal protonated Schiff base. The presence of an enhanced hydrogen out -of -plane band, as well as its sensitivity to the H/D exchange indicate that the retinal chromophore is distorted near the Schiff base region in L. Moreover, the retinal Schiff base of the L state forms a hydrogen bond That is stronger than that of the dark state. These observations are consistent with a Na+ pumping mechanism that involves a proton transfer from the retinal Schiff base to a key aspartate residue (Asp116 in Krokinobacter eikastus rhodopsin 2) in the L/M states.