title: Crystal structures of bR(D85S) favor a model of bacteriorhodopsin as a hydroxyl-ion pump.
abstract: Structural features on the extracellular side of the D85S mutant of bacteriorhodopsin (bR) suggest that wild-type bR could be a hydroxyl-ion pump. A position between the protonated Schiff base and residue 85 serves as an anion-binding site in the mutant protein, and hydroxyl ions should have access to this site during the O-intermediate of the wild-type bR photocycle. The guanidinium group of R82 is proposed (1) to serve as a shuttle that eliminates the Born energy penalty for entry of an anion into this binding pocket, and conversely, (2) to block the exit of a proton or a related proton carrier.
authors.affiliation: Institute for Systems Biology, 1441 North 34th Street, Seattle, WA 98103, USA.
authors.forename: Marc T
authors.initials: MT
authors.lastname: Facciotti
authors.forename: Shahab
authors.initials: S
authors.lastname: Rouhani
authors.forename: Robert M
authors.initials: RM
authors.lastname: Glaeser
mesh_terms: D027321:Anion Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001436:Bacteriorhodopsins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D006878:Hydroxides / Q000378:metabolism*; D017136:Ion Transport; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D011522:Protons
chemical_list: D027321:Anion Transport Proteins; D006878:Hydroxides; D011522:Protons; D001436:Bacteriorhodopsins; C031356:hydroxide ion