HIGH-RESOLUTION STRUCTURE OF BACTERIORHODOPSIN DETERMINED BY ELECTRONCRYSTALLOGRAPHY

Bacteriorhodopsin pumps protons from the cytoplasm to the outside of h alobacteria, Halobacterium salinarium, by using absorbed light energy. The newly observed density map at 3 Angstrom resolution clarified nea rly the entire structure; the resolution in the direction perpendicula r to the membrane surface is 3.2 Angstrom. The new structure clearly i ndicates the proton transfer pathway in bacteriorhodopsin. In particul ar, the location of key aspartic acid and glutamic acid residues in th e derived structural model suggested funneling structures with differe nt designs for input and output of protons on the cytoplasmic and extr acellular sides, respectively, of the protein. This paper describes th e major differences between the model based on the new observation and the former model obtained through crystallographic refinement by Grig orieff et al. (J. Mol. Biol. 259; 393-421, 1996).