title: X-ray-radiation-induced changes in bacteriorhodopsin structure.
abstract: 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.
authors.affiliation: Laboratoire des Protéines Membranaires, Institut de Biologie Structurale J.-P. Ebel, UMR5075 CEA-CNRS-UJF, Grenoble 38027, France.
authors.forename: Valentin I
authors.initials: VI
authors.lastname: Borshchevskiy
authors.forename: Ekaterina S
authors.initials: ES
authors.lastname: Round
authors.forename: Alexandr N
authors.initials: AN
authors.lastname: Popov
authors.forename: Georg
authors.initials: G
authors.lastname: Büldt
authors.forename: Valentin I
authors.initials: VI
authors.lastname: Gordeliy
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D018360:Crystallography, X-Ray / Q000379:methods*; D005583:Fourier Analysis; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D001436:Bacteriorhodopsins