title: Crystal structure of the bromide-bound D85S mutant of bacteriorhodopsin: principles of ion pumping.
abstract: We report the crystal structure of a bromide-bound form of the D85S mutant of bacteriorhodopsin, bR(D85S), a protein that uses light energy rather than ATP to pump halide ions across the cell membrane. Comparison of the structure of the halide-bound and halide-free states reveals that both displacements of individual side-chain positions and concerted helical movements occur on the extracellular side of the protein. Analysis of these structural changes reveals how this ion pump first facilitates ion uptake deep within the cell membrane and then prevents the backward escape of ions later in the pumping cycle. Together with the information provided by structures of intermediate states in the bacteriorhodopsin photocycle, this study also suggests the overall design principles that are necessary for ion pumping.
authors.affiliation: Graduate Group in Biophysics, University of California, Berkeley, California 94720, USA.
authors.forename: Marc T
authors.initials: MT
authors.lastname: Facciotti
authors.forename: Vincent S
authors.initials: VS
authors.lastname: Cheung
authors.forename: Doris
authors.initials: D
authors.lastname: Nguyen
authors.forename: Shahab
authors.initials: S
authors.lastname: Rouhani
authors.forename: Robert M
authors.initials: RM
authors.lastname: Glaeser
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D001665:Binding Sites; D001965:Bromides / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray / Q000379:methods*; D016623:Ion Pumps / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012997:Solvents / Q000737:chemistry; D013329:Structure-Activity Relationship; D013499:Surface Properties
chemical_list: D001965:Bromides; D016623:Ion Pumps; D012997:Solvents; D001436:Bacteriorhodopsins