Cation-Specific Conformations in a Dual-Function Ion-Pumping Microbial Rhodopsin.
Cation-Specific Conformations in a Dual-Function Ion-Pumping Microbial Rhodopsin.
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DOI：
10.1021/bi501386d
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发表时间：
2015-06-30
期刊：
影响因子：
2.9
通讯作者：
Spudich JL
中科院分区：
文献类型：
--
作者：
da Silva GF;Goblirsch BR;Tsai AL;Spudich JL
最近在海洋细菌Dokdonia eikasta中发现的视紫红质离子泵（DeNaR，也称为KR 2）使用光从细胞中泵出质子或钠离子，这取决于介质的离子组成。在悬浮于KCl溶液中的细胞中，DeNaR起到光驱动质子泵的作用，而在NaCl溶液中，DeNaR进行光驱动钠离子泵送，这是视紫红质家族中的一种新活性。这两种不同的功能提出了一个问题，即蛋白质的构象是否在K+或Na+存在下不同，以及导致其他微生物视紫红质经典E → C构象变化的螺旋运动是否在DeNaR中保守。可见光吸收最大值的DeNaR在其unphotolyzed（黑暗）的状态下，Na+和K+在癸基麦芽吡喃糖苷胶束之间的差异为8 nm，这表明阳离子对亚维生素A光活性位点的影响。此外，电子顺磁共振（EPR）光谱的暗态揭示重新定位的螺旋F和G时，K+被替换为Na+。此外，通过EPR自旋-自旋偶极耦合评估的构象变化表明，光诱导的跨膜螺旋运动与在细菌视紫红质中发现的那些非常相似，但是被Na+的存在改变，导致一个新的特征，螺旋F的顺时针旋转。结果建立了控制微生物视紫红质的构象的阳离子开关的第一个观察，并指示特定的相互作用的Na+与DeNaR的半通道打开一个合适的路径离子易位。
A recently discovered rhodopsin ion pump (DeNaR, also known as KR2) in the marine bacterium Dokdonia eikasta uses light to pump protons or sodium ions from the cell depending on the ionic composition of the medium. In cells suspended in a KCl solution, DeNaR functions as a light-driven proton pump, whereas in a NaCl solution, DeNaR conducts light-driven sodium ion pumping, a novel activity within the rhodopsin family. These two distinct functions raise the questions of whether the conformations of the protein differ in the presence of K+ or Na+ and whether the helical movements that result in the canonical E → C conformational change in other microbial rhodopsins are conserved in DeNaR. Visible absorption maxima of DeNaR in its unphotolyzed (dark) state show an 8 nm difference between Na+ and K+ in decyl maltopyranoside micelles, indicating an influence of the cations on the retinylidene photoactive site. In addition, electronic paramagnetic resonance (EPR) spectra of the dark states reveal repositioning of helices F and G when K+ is replaced with Na+. Furthermore, the conformational changes assessed by EPR spin–spin dipolar coupling show that the light-induced transmembrane helix movements are very similar to those found in bacteriorhodopsin but are altered by the presence of Na+, resulting in a new feature, the clockwise rotation of helix F. The results establish the first observation of a cation switch controlling the conformations of a microbial rhodopsin and indicate specific interactions of Na+ with the half-channels of DeNaR to open an appropriate path for ion translocation.