Abstract
Archaeal rhodopsins convert light into energy or signal. Bacteriorhodopsin (BR) and halorhodopsin (HR) are light-driven proton and chloride pumps, respectively. Sensory rhodopsin (sR) and phoborhodopsin (pR) are light sensors for positive and negative phototaxis, respectively. BR is one of the best understood membrane proteins, and the proton-pump mechanism has been extensively studied. We previously showed that replacement of a single amino acid converts BR into a chloride pump like HR. This suggested the mechanism of light-driven ion pumps. By means of infrared spectroscopy of internal water molecules, we have revealed another key element of light-driven proton pump. sR and pR form a complex with their transducer proteins in dark, and light-induced protein structural changes weaken the interaction. Interestingly, sR and pR pump protons in the absence of transducer. It is likely that various functions in archaeal rhodopsins emerge from common structural basis and fine tuning of active centers.
