title: Electron diffraction analysis of structural changes in the photocycle of bacteriorhodopsin.
abstract: Structural changes are central to the mechanism of light-driven proton transport by bacteriorhodopsin, a seven-helix membrane protein. The main intermediate formed upon light absorption is M, which occurs between the proton release and uptake steps of the photocycle. To investigate the structure of the M intermediate, we have carried out electron diffraction studies with two-dimensional crystals of wild-type bacteriorhodopsin and the Asp96-->Gly mutant. The M intermediate was trapped by rapidly freezing the crystals in liquid ethane following illumination with a xenon flash lamp at 5 and 25 degrees C. Here, we present 3.5 A resolution Fourier projection maps of the differences between the M intermediate and the ground state of bacteriorhodopsin. The most prominent structural changes are observed in the vicinity of helices F and G and are localized to the cytoplasmic half of the membrane.
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge, UK.
authors.forename: S
authors.initials: S
authors.lastname: Subramaniam
authors.forename: M
authors.initials: M
authors.lastname: Gerstein
authors.forename: D
authors.initials: D
authors.lastname: Oesterhelt
authors.forename: R
authors.initials: R
authors.lastname: Henderson
mesh_terms: D000595:Amino Acid Sequence; D001224:Aspartic Acid; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003624:Darkness; D004583:Electrons; D005583:Fourier Analysis; D005998:Glycine; D006217:Halobacterium / Q000378:metabolism; D008027:Light; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013057:Spectrum Analysis; D014961:X-Ray Diffraction
chemical_list: D001224:Aspartic Acid; D001436:Bacteriorhodopsins; D005998:Glycine