From structure to mechanism: electron crystallographic studies of bacteriorhodopsin

Bacteriorhodopsin is a protein found in cell membranes of the organism H. salinarum, where it functions as an efficient light-driven proton pump. Because bacteriorhodopsin is one of the simplest ion pumps known in biology, it has been the subject of intensive investigations over the last three decades, using methods spanning the range from femtosecond spectroscopy and crystallography to biochemistry and molecular biology. Here, we focus on the structural basis for the function of this protein, with primary emphasis on the contributions of electron microscopy and crystallography towards unravelling the mechanism of vectorial proton pumping.