Water Molecules in Short- and Long-Distance Proton Transfer Steps of Bacteriorhodopsin Proton Pumping

The proton pumping cycle of bacteriorhodopsin consists of five consecutive proton transfer steps, in all of which water molecules are likely to play critical roles. Here we review the role of water molecules in bacteriorhodopsin function, with emphasis oil computations of the retinal Schiff base deprotonation reaction and the open questions regarding the participation of water molecules in the longer-distance proton transfer reactions.