This paper is part of the Proceedings of the 13th International Conference on Retinal Proteins, Barcelona, Spain, 15–19 June 2008.
Role of Arg123 in Light-driven Anion Pump Mechanisms of pharaonis Halorhodopsin†
Article first published online: 25 FEB 2009
© 2009 The Authors. Journal Compilation. The American Society of Photobiology
Photochemistry and Photobiology
Volume 85, Issue 2, pages 547–555, March/April 2009
How to Cite
Kubo, M., Kikukawa, T., Miyauchi, S., Seki, A., Kamiya, M., Aizawa, T., Kawano, K., Kamo, N. and Demura, M. (2009), Role of Arg123 in Light-driven Anion Pump Mechanisms of pharaonis Halorhodopsin. Photochemistry and Photobiology, 85: 547–555. doi: 10.1111/j.1751-1097.2009.00538.x
- Issue published online: 25 FEB 2009
- Article first published online: 25 FEB 2009
- Received 6 September 2008, accepted 8 December 2008
Halorhodopsin (HR) acts as a light-driven chloride pump which transports a chloride ion from the extracellular (EC) to the cytoplasmic space during a photocycle reaction that includes some photointermediates initiated by illumination. To understand the chloride uptake mechanisms, we focused on a basic residue Arg123 of HR from Natronomonas pharaonis (NpHR), which is the only basic residue located in the EC half ion channel. By the measurements of the visible absorption spectra in the dark and the light-induced inward current through the membrane, it was shown that the chloride binding and transport ability of NpHR completely disappeared by the change of arginine to glutamine. From flashphotolysis analysis, the photocycle of R123Q differed from that of wildtype NpHR completely. The response of the R123H mutant depended on pH. These facts imply that the positive charge at position 123 is essential for chloride binding in the ground state and for the chloride uptake under illumination. On the basis of the molecular structures of HR and the anion-transportable mutants of bacteriorhodopsin, the effects of the positive charge and the conformational change of the Arg123 side chain as well as the chloride-pumping mechanism are discussed.