X-ray-radiation-induced changes in bacteriorhodopsin structure

Bacteriorhodopsin (bR) provides light-driven vectorial proton transport across a cell membrane. Creation of electrochemical potential at the membrane is a universal step in energy transformation in a cell. Published atomic crystallographic models of early intermediate states of bR show a significant difference between them, and conclusions about pumping mechanisms have been contradictory. Here, we present a quantitative high-resolution crystallographic study of conformational changes in bR induced by X-ray absorption. It is shown that X-ray doses that are usually accumulated during data collection for intermediate-state studies are sufficient to significantly alter the structure of the protein. X-ray-induced changes occur primarily in the active site of bR. Structural modeling showed that X-ray absorption triggers retinal isomerization accompanied by the disappearance of electron densities corresponding to the water molecule W402 bound to the Schiff base. It is demonstrated that these and other X-ray-induced changes may mimic functional conformational changes of bR leading to misinterpretation of the earlier obtained X-ray crystallographic structures of photointermediates

Comparative analysis of the quality of membrane protein bacteriorhodopsin crystals during crystallization in octylglucoside and octylthioglucoside

Crystallization of bacteriorhodopsin (bR) in the lipidic cubic phase using n-octyl-beta-D-glucoside (OG) and its more stable and inexpensive analogue n-octyl-beta-D-thioglucoside (OTG) was comparatively analyzed [1]. It was shown that bacteriorhodopsin is efficiently crystallized in OTG in the same detergent concentration range as in OG. However, x-ray diffraction analysis shows that bR crystals in OG are characterized by a better resolution (1.35 A...) than bR crystals in OTG (1.45 A...)