title: High-resolution powder diffraction study of purple membrane with a large Guinier-type camera.
abstract: X-ray diffraction patterns from a film of oriented purple membranes, which comprise two-dimensional crystals of bacteriorhodopsin (BR) trimers, were recorded with a 1 m-pathlength Guinier-type camera at SPring-8 BL40B2. A well focused X-ray beam and a camera with a high angular resolution of 0.024 degrees enabled a powder diffraction profile with very sharp and well separated peaks to be obtained up to a resolution of 2.3 A. Using integrated diffraction intensities up to a Bragg spacing of 4.2 A, a cluster of bulky amino acid residues and the head group of the BR chromophore are apparent in the electron density map projected along the membrane normal. Thus, a combination of synchrotron X-rays and large Guinier camera can be used for analyzing the conformational changes of BR in the intact state. In addition, the method might be extended to the structural analysis of film materials composed of two-dimensional arrays of nanoparticles.
authors.affiliation: Department of Physics, Faculty of Science and Technology, Keio University, Japan. oka@phys.keio.ac.jp
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Oka
authors.forename: Keiko
authors.initials: K
authors.lastname: Miura
authors.forename: Katsuaki
authors.initials: K
authors.lastname: Inoue
authors.forename: Tatzuo
authors.initials: T
authors.lastname: Ueki
authors.forename: Naoto
authors.initials: N
authors.lastname: Yagi
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D019617:Halobacterium salinarum / Q000737:chemistry*; D007089:Image Enhancement / Q000295:instrumentation*; D033362:Powder Diffraction / Q000295:instrumentation*; D018717:Purple Membrane / Q000000981:diagnostic imaging*; D014159:Transducers; D014463:Ultrasonography