Where is the pump switch of bacteriorhodopsin located?

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This research project aims at revealing the mechanism of proton pump in bacteriorhodopsin(BR). For this aim, we applied low-temperature polarized Fourier-transform infrared(FTIR) spectroscopy. Highly accurate FTIR spectroscopy of BR and related proteins provided the following results.(1)A new model for the primary proton transfer reaction is proposed based on the detailed structural analysis of internal water molecules in BR by low-temperature FTIR spectroscopy. This method led to the so called "hydration switch model". According to the model, the proton transfer reaction is controlled by a hydration switch of a water molecule from Asp85 to Asp212.(2)By use of isotope label and mutant proteins, we identified stretching vibrations of the protonated Schiff base and Arg82,both of which constitute hydrogen-bonding network in BR.(3)Hydrogen-bonding network in halorhodopsin, a light-driven chloride ion pump, is studied. We found that a chloride ion is hydrated by internal water molecules differently from those in BR.(4)Complex formation between pharaonis phoborhodopsin and its transducer protein was detected by FTIR spectroscopy.(5)Protein structural changes of Neurospora rhodopsin and visual rhodopsin were studied. Unique hydrogen-bonding structures are revealed.