Hasegawa Chisa, Kikukawa Takashi, Miyauchi Seiji, Seki Akiteru, Sudo Yuki, Kubo Megumi, Demura Makoto, Kamo Naoki
Laboratory of Biophysical Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Photochem Photobiol. 2007 Mar-Apr;83(2):293-302. doi: 10.1562/2006-06-09-RA-916.
An alkali-halophilic archaeum, Natronomonas pharaonis, contains two rhodopsins that are halorhodopsin (phR), a light-driven inward Cl- pump and phoborhodopsin (ppR), the receptor of negative phototaxis functioning by forming a signaling complex with a transducer, pHtrII (Sudo Y. et al., J. Mol. Biol. 357 [2006] 1274). Previously, we reported that the phR double mutant, P240T/F250Y(phR), can bind with pHtrII. This mutant itself can transport Cl-, while the net transport was stopped upon formation of the complex. The flash-photolysis data were analyzed by a scheme in which phR --> 4 P1 --> P2 --> 4 P3 --> P4 --> phR. The P3 of the wild-type and the double mutant contained two components, X- and O-intermediates. After the complex formation, however, the P3 of the double mutant lacked the X-intermediate. These observations imply that the X-intermediate (probably the N-intermediate) is the state having Cl- in the cytoplasmic binding site and that the complex undergoes an extracellular Cl- circulation because of the inhibition of formation of the X-intermediate.
嗜碱古菌法老盐单胞菌含有两种视紫红质，即卤视紫红质（phR），一种光驱动的内向氯离子泵，以及噬光视紫红质（ppR），它是负趋光性的受体，通过与转导蛋白pHtrII形成信号复合物发挥作用（Sudo Y.等人，《分子生物学杂志》357 [2006] 1274）。此前，我们报道了phR双突变体P240T/F250Y(phR)能够与pHtrII结合。该突变体自身能够转运氯离子，而在复合物形成后净转运停止。通过phR --> 4 P1 --> P2 --> 4 P3 --> P4 --> phR的模式分析闪光光解数据。野生型和双突变体的P3包含两个组分，即X中间体和O中间体。然而，复合物形成后，双突变体的P3缺少X中间体。这些观察结果表明，X中间体（可能是N中间体）是细胞质结合位点含有氯离子的状态，并且由于X中间体形成的抑制，复合物经历细胞外氯离子循环。
