Structural Mechanism for Light-driven Transport by a New Type of Chloride Ion Pump, Nonlabens marinus Rhodopsin-3
Structural Mechanism for Light-driven Transport by a New Type of Chloride Ion Pump, Nonlabens marinus Rhodopsin-3
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DOI：
10.1074/jbc.m116.728220
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发表时间：
2016-08-19
影响因子：
4.8
通讯作者：
Shirouzu, Mikako
中科院分区：
文献类型：
--
作者：
Hosaka, Toshiaki;Yoshizawa, Susumu;Shirouzu, Mikako
来自海洋黄杆菌的光驱动的向内氯离子泵激视紫红质Nonlabens marinus rhodopsin-3（NM-R3）属于与被称为古细菌向内氯离子泵激视紫红质的盐视紫红质不同的系统发育谱系。NM-R3和盐视紫红质具有不同的基序序列，其对于氯离子结合和转运是重要的。在这项研究中，我们提出了一种新型的光驱动氯离子泵，NM-R3，在1.58分辨率的晶体结构。该结构揭示了氯离子易位途径，并表明一个单一的氯离子附近的席夫碱。NM-R3的整体结构、氯离子结合位点和转运途径与盐视紫红质不同。出乎意料的是，这种NM-R3结构与光驱动的外向钠离子泵Krokinaseikastus rhodopsin 2的晶体结构相似。NM-R3的结构和突变分析表明，大多数用于氯离子泵送的重要氨基酸残基存在于位于NM-R3细胞外侧的离子流入区。相反，在另一侧，K.据报道，Eikastus视紫红质2对于钠离子泵送是重要的。这些结果提供了新的见解离子泵视紫红质，其中向内和向外泵的离子流入区域的离子选择性是重要的离子选择性的离子选择机制。
The light-driven inward chloride ion-pumping rhodopsin Nonlabens marinus rhodopsin-3 (NM-R3), from a marine flavobacterium, belongs to a phylogenetic lineage distinct from the halorhodopsins known as archaeal inward chloride ion-pumping rhodopsins. NM-R3 and halorhodopsin have distinct motif sequences that are important for chloride ion binding and transport. In this study, we present the crystal structure of a new type of light-driven chloride ion pump, NM-R3, at 1.58 resolution. The structure revealed the chloride ion translocation pathway and showed that a single chloride ion resides near the Schiff base. The overall structure, chloride ion-binding site, and translocation pathway of NM-R3 are different from those of halorhodopsin. Unexpectedly, this NM-R3 structure is similar to the crystal structure of the light-driven outward sodium ion pump, Krokinobacter eikastus rhodopsin 2. Structural and mutational analyses of NM-R3 revealed that most of the important amino acid residues for chloride ion pumping exist in the ion influx region, located on the extracellular side of NM-R3. In contrast, on the opposite side, the cytoplasmic regions of K. eikastus rhodopsin 2 were reportedly important for sodium ion pumping. These results provide new insight into ion selection mechanisms in ion pumping rhodopsins, in which the ion influx regions of both the inward and outward pumps are important for their ion selectivities.