CRYSTALLOGRAPHIC DESCRIPTION OF THE PHOTOINTERMEDIATES OF BACTERIORHODOPSIN

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Bacteriorhodopsin crystals we have grown in cubic lipid phase diffract to nearly 1.4 ¿¿ and promise to yield structural information on the reaction cycle intermediates, K, L, M, N and O, of this light-driven proton pump. By illumination of wild-type and mutant crystals under various conditions, a few M sub-states could be produced with 100% occupancy, but most intermediates accumulate to 40-60% only. Refinement of the second conformation in the models is difficult, and confidence in the conclusions depends on high-resolution data from numerous duplicate experiments. Data sets we collected to 1.43 ¿¿resolution have been encouraging, and produced preliminary information about the twisted retinal chromophore in the K state and its changes in an early M state. We propose to continue these experiments with the best synchrotron beam available, and to describe, for the first time for any ion pump, the transport mechanism in detailed molecular terms.