Structural studies of bacteriorhodopsin in BC era.

It marked half a century since the discovery of bacteriorhodopsin two years ago. On this occasion, I have revisited historically important diffraction studies of this membrane protein, based on my recollections. X-ray diffraction and electron diffraction, and electron microscopy, described the low-resolution structure of bacteriorhodopsin within the purple membrane. Neutron diffraction was effective to assign the helical regions in the primary structure with 7 rods revealed by low-resolution structure as well as to describe the retinal position. Substantial conformational changes upon light illumination were clarified by the structures of various photointermediates. Early trials of time-resolved studies were also introduced. Models for the mechanism of light-driven proton pump based on the low-resolution structural studies are also described. Significantly, they are not far from the today's understanding. I believe that the spirit of the early research scientists in this field and the essence of their studies, which constitute the foundations of the field, still actively fertilizes current membrane protein research.