title: Structural changes in bacteriorhodopsin during ion transport at 2 angstrom resolution.
abstract: Crystal structures of the Asp96 to Asn mutant of the light-driven proton pump bacteriorhodopsin and its M photointermediate produced by illumination at ambient temperature have been determined to 1.8 and 2.0 angstroms resolution, respectively. The trapped photoproduct corresponds to the late M state in the transport cycle-that is, after proton transfer to Asp85 and release of a proton to the extracellular membrane surface, but before reprotonation of the deprotonated retinal Schiff base. Its density map describes displacements of side chains near the retinal induced by its photoisomerization to 13-cis,15-anti and an extensive rearrangement of the three-dimensional network of hydrogen-bonded residues and bound water that accounts for the changed pKa values (where Ka is the acid constant) of the Schiff base and Asp85. The structural changes detected suggest the means for conserving energy at the active site and for ensuring the directionality of proton translocation.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, USA. hudel@uci.edu
authors.forename: H
authors.initials: H
authors.lastname: Luecke
authors.forename: B
authors.initials: B
authors.lastname: Schobert
authors.forename: H T
authors.initials: HT
authors.lastname: Richter
authors.forename: J P
authors.initials: JP
authors.lastname: Cartailler
authors.forename: J K
authors.initials: JK
authors.lastname: Lanyi
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003593:Cytoplasm / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D007536:Isomerism; D008027:Light; D008958:Models, Molecular; D010782:Photolysis; D017785:Photons; D017354:Point Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017494:Proton Pumps / Q000737:chemistry* / Q000378:metabolism*; D011522:Protons; D012172:Retinaldehyde / Q000737:chemistry / Q000378:metabolism; D012545:Schiff Bases; D013816:Thermodynamics; D014867:Water
chemical_list: D017494:Proton Pumps; D011522:Protons; D012545:Schiff Bases; D014867:Water; D001436:Bacteriorhodopsins; D012172:Retinaldehyde