Allosteric Communication with the Retinal Chromophore upon Ion Binding in a Light-Driven Sodium Ion-Pumping Rhodopsin.,Biochemistry

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Allosteric Communication with the Retinal Chromophore upon Ion Binding in a Light-Driven Sodium Ion-Pumping Rhodopsin.
Biochemistry ( IF 2.9 ) Pub Date : 2020-01-09 , DOI: 10.1021/acs.biochem.9b01062
Akihiro Otomo ₁ , Misao Mizuno ₁ , Keiichi Inoue ₂ , Hideki Kandori _{3,

4} , Yasuhisa Mizutani ₁

Affiliation

Krokinobacter rhodopsin 2 (KR2) serves as a light-driven sodium ion pump in the presence of sodium ion and works as a proton pump in the presence of larger monovalent cations such as potassium ion, rubidium ion, and cesium ion. Recent crystallographic studies revealed that KR2 forms a pentamer and possesses an ion binding site at the subunit interface. It is assumed that sodium ion bound at this binding site is not transported but contributes to the thermal stability. Because KR2 can convert its function in response to coexisting cation species, this ion binding site is likely to be involved in ion transport selectively. However, how sodium ion binding affects the structure of the retinal chromophore, which plays a crucial role in ion transport, remains poorly understood. Here, we observed the structure of the retinal chromophore under a wide range of cation concentrations using visible absorption and resonance Raman spectroscopy. We discovered that the hydrogen bond formed between the Schiff base of the retinal chromophore and its counterion, Asp116, is weakened upon binding of sodium ion. This allosteric communication between the Schiff base and the ion binding site at the subunit interface likely increases the apparent efficiency of sodium ion transport. In addition, this study demonstrates the significance of sodium ion binding: even though sodium ion is not transported, binding regulates the structure around the Schiff base and stabilizes the oligomeric structure.

中文翻译：

在光驱动钠离子泵视紫红质上离子结合后与视网膜发色团的变构通讯。

假单胞菌视紫红质2（KR2）在存在钠离子的情况下充当光驱动钠离子泵，在存在较大的单价阳离子（例如钾离子，rub离子和铯离子）的情况下充当质子泵。最近的晶体学研究表明，KR2形成五聚体，并在亚基界面处具有离子结合位点。假定在该结合位点结合的钠离子不被运输而是有助于热稳定性。由于KR2可以响应于共存的阳离子种类而转换其功能，因此该离子结合位点可能会选择性地参与离子迁移。但是，钠离子结合如何影响视网膜发色团的结构，在离子运输中起着至关重要的作用，对此仍然知之甚少。这里，我们使用可见光吸收和共振拉曼光谱观察了在宽范围的阳离子浓度下的视网膜发色团的结构。我们发现，在视网膜发色团的席夫碱及其抗衡离子Asp116之间形成的氢键在结合钠离子时被削弱。Schiff碱与亚基界面处的离子结合位点之间的这种变构通讯可能会增加钠离子转运的表观效率。此外，这项研究证明了钠离子结合的重要性：即使钠离子不被转运，结合也能调节席夫碱周围的结构并稳定寡聚结构。我们发现，在视网膜发色团的席夫碱及其抗衡离子Asp116之间形成的氢键在结合钠离子时被削弱。Schiff碱与亚基界面处的离子结合位点之间的这种变构通讯可能会增加钠离子转运的表观效率。另外，这项研究证明了钠离子结合的重要性：即使钠离子不被转运，结合也能调节席夫碱周围的结构并稳定寡聚结构。我们发现，在视网膜发色团的席夫碱及其抗衡离子Asp116之间形成的氢键在结合钠离子时被削弱。Schiff碱与亚基界面处的离子结合位点之间的这种变构通讯可能会增加钠离子转运的表观效率。另外，这项研究证明了钠离子结合的重要性：即使钠离子不被转运，结合也能调节席夫碱周围的结构并稳定寡聚结构。

更新日期：2020-01-09

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