title: Detection and characterization of merohedral twinning in two protein crystals: bacteriorhodopsin and p67(phox).
abstract: The estimation of the twinning ratio in crystals of two proteins, bacteriorhodopsin and a truncated form of p67(phox), is described. Various approaches are combined to detect and determine accurately the twinning ratio. For each protein, three data sets from crystals exhibiting twinning ratios ranging from 0 to almost 50% are analysed. Self-rotation functions and R(sym) values considering space groups of higher symmetry are indicative of twinning. Precise values of the twinning ratios are derived from Yeates' statistical approaches and Britton plots. The twinning ratios are also obtained by analysing the second-, third- and fourth-order moments of the intensity distribution. The twinning ratios obtained from the various approaches are compared. Second-, third- and fourth-order moments of the intensity distribution are useful indicators for evaluating the twinning precisely in order to correct the intensities or to screen rapidly for non-twinned crystals.
authors.affiliation: Institut de Biologie Structurale, CEA-CNRS-Université Joseph Fourier UMR5075, 41 Rue Jules Horowitz, F-38027 Grenoble CEDEX 1, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Royant
authors.forename: Sylvestre
authors.initials: S
authors.lastname: Grizot
authors.forename: Richard
authors.initials: R
authors.lastname: Kahn
authors.forename: Hassan
authors.initials: H
authors.lastname: Belrhali
authors.forename: Franck
authors.initials: F
authors.lastname: Fieschi
authors.forename: Ehud M
authors.initials: EM
authors.lastname: Landau
authors.forename: Eva
authors.initials: E
authors.lastname: Pebay-Peyroula
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019617:Halobacterium salinarum / Q000737:chemistry; D009504:Neutrophils / Q000737:chemistry; D010750:Phosphoproteins / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D010750:Phosphoproteins; C079789:neutrophil cytosol factor 67K; D001436:Bacteriorhodopsins