title: Light- and dark-adapted bacteriorhodopsin, a time-resolved neutron diffraction study.
abstract: Recently, neutron diffraction experiments have revealed well-resolved and reversible changes in the protein conformation of bacteriorhodopsin (BR) between the light-adapted ground state and the M-intermediate of the proton pumping photocycle (Dencher, Dresselhaus, Zaccai and Büldt (1989) Proc. Natl. Acad. Sci. USA 86, 7876-7879). These changes are triggered by the light-induced isomerization of the chromophore retinal from the all-trans to the 13-cis configuration. Dark-adapted purple membranes contain a mixture of two pigment species with either the all-trans- or 13-cis-retinal isomer as chromophore. Employing a time-resolved neutron diffraction technique, no changes in protein conformation in the resolution regime of up to 7 A are observed during the transition between the two ground-state species 13-cis-BR and all-trans-BR. This is in line with the fact that the conversion of all-trans BR to 13-cis-BR involves an additional isomerization about the C15 = N Schiff's base bond, which in contrast to M formation minimizes retinal displacement and keeps the Schiff's base in the original protein environment. Furthermore, there is no indication for large-scale redistribution of water molecules in the purple membrane during light-dark adaptation.
authors.affiliation: Department of Physics/Biophysics, Freie Universität Berlin, Germany.
authors.forename: N A
authors.initials: NA
authors.lastname: Dencher
authors.forename: G
authors.initials: G
authors.lastname: Papadopoulos
authors.forename: D
authors.initials: D
authors.lastname: Dresselhaus
authors.forename: G
authors.initials: G
authors.lastname: Büldt
mesh_terms: D001436:Bacteriorhodopsins; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003623:Dark Adaptation; D006217:Halobacterium / Q000032:analysis; D008027:Light; D009502:Neutrons; D011487:Protein Conformation; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D001436:Bacteriorhodopsins