title: High-resolution X-ray structure of an early intermediate in the bacteriorhodopsin photocycle.
abstract: Bacteriorhodopsin is the simplest known photon-driven proton pump and as such provides a model for the study of a basic function in bioenergetics. Its seven transmembrane helices encompass a proton translocation pathway containing the chromophore, a retinal molecule covalently bound to lysine 216 through a protonated Schiff base, and a series of proton donors and acceptors. Photoisomerization of the all-trans retinal to the 13-cis configuration initiates the vectorial translocation of a proton from the Schiff base, the primary proton donor, to the extracellular side, followed by reprotonation of the Schiff base from the cytoplasm. Here we describe the high-resolution X-ray structure of an early intermediate in the photocycle of bacteriorhodopsin, which is formed directly after photoexcitation. A key water molecule is dislocated, allowing the primary proton acceptor, Asp 85, to move. Movement of the main-chain Lys 216 locally disrupts the hydrogen-bonding network of helix G, facilitating structural changes later in the photocycle.
authors.affiliation: Department of Biochemistry, Uppsala University, Biomedical Centre, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Edman
authors.forename: P
authors.initials: P
authors.lastname: Nollert
authors.forename: A
authors.initials: A
authors.lastname: Royant
authors.forename: H
authors.initials: H
authors.lastname: Belrhali
authors.forename: E
authors.initials: E
authors.lastname: Pebay-Peyroula
authors.forename: J
authors.initials: J
authors.lastname: Hajdu
authors.forename: R
authors.initials: R
authors.lastname: Neutze
authors.forename: E M
authors.initials: EM
authors.lastname: Landau
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D008027:Light; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010777:Photochemistry
chemical_list: D001436:Bacteriorhodopsins