title: Water-containing hydrogen-bonding network in the active center of channelrhodopsin.
abstract: Channelrhodopsin (ChR) functions as a light-gated ion channel in Chlamydomonas reinhardtii. Passive transport of cations by ChR is fundamentally different from the active transport by light-driven ion pumps such as archaerhodopsin, bacteriorhodopsin, and halorhodopsin. These microbial rhodopsins are important tools for optogenetics, where ChR is used to activate neurons by light, while the ion pumps are used for neural silencing. Ion-transport functions by these rhodopsins strongly depend on the specific hydrogen-bonding networks containing water near the retinal chromophore. In this work, we measured protein-bound water molecules in a chimeric ChR protein of ChR1 (helices A to E) and ChR2 (helices F and G) of Chlamydomonas reinhardtii using low-temperature FTIR spectroscopy at 77 K. We found that the active center of ChR possesses more water molecules (9 water vibrations) than those of other microbial (2-6 water vibrations) and animal (6-8 water vibrations) rhodopsins. We conclude that the protonated retinal Schiff base interacts with the counterion (Glu162) directly, without the intervening water molecule found in proton-pumping microbial rhodopsins. The present FTIR results and the recent X-ray structure of ChR reveal a unique hydrogen-bonding network around the active center of this light-gated ion channel.
authors: Department of Frontier Materials, Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555, Japan.
authors: Shota
authors: S
authors: Ito
authors: Hideaki E
authors: HE
authors: Kato
authors: Reiya
authors: R
authors: Taniguchi
authors: Tatsuya
authors: T
authors: Iwata
authors: Osamu
authors: O
authors: Nureki
authors: Hideki
authors: H
authors: Kandori
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii; D006860:Hydrogen Bonding; D007536:Isomerism; D008958:Models, Molecular; D009154:Mutation; D055668:Photochemical Processes; D017433:Protein Structure, Secondary; D013696:Temperature; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D001436:Bacteriorhodopsins