Settling the Long-Standing Debate on the Proton Storage Site of the Prototype Light-Driven Proton Pump Bacteriorhodopsin.

Despite decades of research, the location and molecular identity of the proton release group together with the subsequent proton release pathway remain controversial even for the simplest light-driven proton pump, bacteriorhodopsin, according to the most recent experiments and simulations. Yet despite this nagging lack of knowledge for the generic case, even more complex pumps are currently under investigation. The proton release group disclosed by our large-scale simulations satisfies available experimental results, especially the broad Zundel continuum absorption subject to a striking anisotropy observed only recently. Moreover, our simulations delineate the seamless pathway by which the excess proton (being stored in an ultrastrong centered H-bond involving two glutamates) is finally translocated into the extracellular medium.