Sudo Y, Iwamoto M, Shimono K, Sumi M, Kamo N
Laboratory of Biophysical Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan.
Biophys J. 2001 Feb;80(2):916-22. doi: 10.1016/S0006-3495(01)76070-5.
Phoborhodopsin (pR; also sensory rhodopsin II, sRII) is a retinoid protein in Halobacterium salinarum and works as a receptor of negative phototaxis. Pharaonis phoborhodopsin (ppR; also pharaonis sensory rhodopsin II, psRII) is a corresponding protein of Natronobacterium pharaonis. In bacterial membrane, ppR forms a complex with its transducer pHtrII, and this complex transmits the light signal to the sensory system in the cytoplasm. We expressed pHtrII-free ppR or ppR-pHtrII complex in H. salinarum Pho81/wr(-) cells. Flash-photolysis experiments showed no essential changes between pHtrII-free ppR and the complex. Using SnO2 electrode, which works as a sensitive pH electrode, and envelope membrane vesicles, we showed the photo-induced outward proton transport. This membranous proton transport was also shown using membrane vesicles from Escherichia coli in which ppR was functionally expressed. On the other hand, the proton transport was ceased when ppR formed a complex with pHtrII. Using membrane sheet, it was shown that the complex undergoes first proton uptake and then release during the photocycle, the same as pHtrII-free ppR, although the net proton transport ceases. Taking into consideration that the complex of sRII (pR) and its transducer undergoes extracellular proton circulation (J. Sasaki and J. L., Biophys. J. 77:2145-2152), we inferred that association with pHtrII closes a cytoplasmic channel of ppR, which lead to the extracellular proton circulation.
嗜盐菌视紫红质（pR；也称为感光视紫红质II，sRII）是盐生盐杆菌中的一种类视黄醇蛋白，作为负趋光性的受体发挥作用。法老嗜盐菌视紫红质（ppR；也称为法老感光视紫红质II，psRII）是嗜盐碱杆菌的一种相应蛋白。在细菌膜中，ppR与其转导蛋白pHtrII形成复合物，该复合物将光信号传递到细胞质中的感觉系统。我们在盐生盐杆菌Pho81/wr(-)细胞中表达了无pHtrII的ppR或ppR-pHtrII复合物。闪光光解实验表明，无pHtrII的ppR与复合物之间没有本质变化。使用作为灵敏pH电极的SnO2电极和包膜膜囊泡，我们展示了光诱导的外向质子运输。在功能上表达了ppR的大肠杆菌膜囊泡中也展示了这种膜质子运输。另一方面，当ppR与pHtrII形成复合物时，质子运输停止。使用膜片表明，与无pHtrII的ppR一样，该复合物在光循环过程中先摄取质子然后释放质子，尽管净质子运输停止。考虑到sRII（pR）与其转导蛋白的复合物经历细胞外质子循环（J. Sasaki和J. L.，《生物物理杂志》77:2145 - 2152），我们推断与pHtrII的结合会关闭ppR的细胞质通道，从而导致细胞外质子循环。
