X-RAY STRUCTURE OF BACTERIORHODOPSIN AT 2.5 ANGSTROMS FROM MICROCRYSTALS GROWN IN LIPIDIC CUBIC PHASES

Lipidic cubic phases provide a continuous three-dimensional bilayer ma trix that facilitates nucleation and growth of bacteriorhodopsin micro crystals. The crystals diffract x-rays isotropically to 2.0 angstroms. The structure of this light-driven proton pump was solved at a resolu tion of 2.5 angstroms by molecular replacement, using previous results from electron crystallographic studies as a model, The earlier struct ure was generally confirmed, but several differences were found, inclu ding loop conformations and side chain residues, Eight water molecules are now identified experimentally in the proton pathway. These findin gs reveal the constituents of the proton translocation pathway in the ground state.