The Institute for Solid State Physics, The University of Tokyo, Chiba, Japan.
Department of Chemistry, Graduate School of Science, Chiba University, Chiba, Japan.
J Biol Chem. 2024 Oct;300(10):107797. doi: 10.1016/j.jbc.2024.107797. Epub 2024 Sep 19.
Microbial rhodopsins are photoreceptive membrane proteins found in microorganisms with an all-trans-retinal chromophore. The function of many microbial rhodopsins is determined by three residues in the third transmembrane helix called motif residues. Here, we report a group of microbial rhodopsins with a novel Thr-Thr-Gly (TTG) motif. The ion-transport assay revealed that they function as light-driven inward anion pumps similar to halorhodopsins previously found in archaea and bacteria. Based on the characteristic glycine residue in their motif and light-driven anion-pumping function, these new rhodopsins are called glycylhalorhodopsins (GHRs). X-ray crystallographic analysis found large cavities on the cytoplasmic side, which are produced by the small side-chain volume of the glycine residue in the motif. The opened structure of GHR on the cytoplasmic side is related to the anion releasing process to the cytoplasm during the photoreaction compared to canonical halorhodopsin from Natronomonas pharaonis (NpHR). GHR also transports SO and the extracellular glutamate residue plays an essential role in extracellular SO uptake. In summary, we have identified TTG motif-containing microbial rhodopsins that display an anion-releasing mechanism.
微生物视紫红质是一种存在于微生物中的光受体膜蛋白，其含有全反式视黄醛发色团。许多微生物视紫红质的功能由第三跨膜螺旋中称为基序残基的三个残基决定。在这里，我们报告了一组具有新型 Thr-Thr-Gly (TTG) 基序的微生物视紫红质。离子转运测定表明，它们作为光驱动内向阴离子泵发挥作用，类似于先前在古菌和细菌中发现的盐细菌视紫红质。基于其基序中的特征性甘氨酸残基和光驱动阴离子泵功能，这些新的视紫红质被称为甘氨酰盐细菌视紫红质 (GHR)。X 射线晶体学分析发现细胞质侧有大的空腔，这是由基序中甘氨酸残基的小侧链体积产生的。与来自嗜盐古菌 (Natronomonas pharaonis，NpHR) 的经典盐细菌视紫红质相比，GHR 在细胞质侧的打开结构与光反应期间阴离子向细胞质释放的过程有关。GHR 还转运 SO，细胞外谷氨酸残基在外源性 SO 摄取中起重要作用。总之，我们已经鉴定出含有 TTG 基序的微生物视紫红质，其显示出阴离子释放机制。
