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J Mol Biol. 2011 Jun 24;409(5):813-25. doi: 10.1016/j.jmb.2011.04.038. Epub 2011 Apr 21.

X-ray-radiation-induced changes in bacteriorhodopsin structure.

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Laboratoire des Protéines Membranaires, Institut de Biologie Structurale J.-P. Ebel, UMR5075 CEA-CNRS-UJF, Grenoble 38027, France.


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.

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