title: Crystallization of bacteriorhodopsin from bicelle formulations at room temperature.
abstract: We showed previously that high-quality crystals of bacteriorhodopsin (bR) from Halobacterium salinarum can be obtained from bicelle-forming DMPC/CHAPSO mixtures at 37 degrees C. As many membrane proteins are not sufficiently stable for crystallization at this high temperature, we tested whether the bicelle method could be applied at a lower temperature. Here we show that bR can be crystallized at room temperature using two different bicelle-forming compositions: DMPC/CHAPSO and DTPC/CHAPSO. The DTPC/CHAPSO crystals grown at room temperature are essentially identical to the previous, twinned crystals: space group P21 with unit cell dimensions of a = 44.7 A, b = 108.7 A, c = 55.8 A, beta = 113.6 degrees . The room-temperature DMPC/CHAPSO crystals are untwinned, however, and belong to space group C222(1) with the following unit cell dimensions: a = 44.7 A, b = 102.5 A, c = 128.2 A. The bR protein packs into almost identical layers in the two crystal forms, but the layers stack differently. The new untwinned crystal form yielded clear density for a previously unresolved CHAPSO molecule inserted between protein subunits within the layers. The ability to grow crystals at room temperature significantly expands the applicability of bicelle crystallization.
authors.affiliation: Department of Chemistry and Biochemistry, UCLA-DOE Center for Genomics and Proteomics, Molecular Biology Institute, University of California, Los Angeles, California 90095-1570, USA.
authors.forename: Salem
authors.initials: S
authors.lastname: Faham
authors.forename: Gabriella L
authors.initials: GL
authors.lastname: Boulting
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Massey
authors.forename: Sarah
authors.initials: S
authors.lastname: Yohannan
authors.forename: Dawn
authors.initials: D
authors.lastname: Yang
authors.forename: James U
authors.initials: JU
authors.lastname: Bowie
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics; D002793:Cholic Acids; D003460:Crystallization; D004134:Dimyristoylphosphatidylcholine; D009154:Mutation; D017434:Protein Structure, Tertiary; D013696:Temperature
chemical_list: D002793:Cholic Acids; D001436:Bacteriorhodopsins; C048531:chapso; D004134:Dimyristoylphosphatidylcholine