Deconvolution of fully overlapped reflections from crystals of foot-and-mouth disease virus O₁G67

Abstract

Foot-and-mouth disease virus O1 G67 forms crystals that appear similar to those of the closely related viruses OiK and O~BFS, both of which belong to space group I23. Statistical disorder in the O, G67 crystals means, however, that the measured diffraction data possess higher symmetry consistent with point group 432. It is shown that this is due to intimate twinning, with mosaic blocks randomly distributed between the two orientations. This results in a twofold loss of information due to the exact superimposition of non-identical reflections from the two orientations. A simple procedure has been devised to deconvolute these overlapped reflections by applying constraints in both real and reciprocal space. This procedure works well, providing interpretable electron-density maps for this virus. Other applications are discussed.

Structural comparison of two strains of foot-and-mouth disease virus subtype O1 and a laboratory antigenic variant, G67

“…The data were processed in point group 432 and therefore could not be simply matched to the other 01 data sets and the available phases. As previously described [32], pseudo-432 intensities calculated as the arithmetic mean of the 123 intensities for reflection pairs h,k,l and k,h,l provided an excellent model of the observed G67 data. Comparisons between the other 01 viruses and G67 were therefore made by producing such pseudo-432 data sets for each virus which were scaled (as before with calculation of Rmatch and Cmatch; Table 3) to the G67 data.…”

“…Within crystals of O 1 K and O 1 BFS, all the particles within a single crystal adopt the same orientation, whereas in our crystals of G67, 50% of the virions adopt one orientation and 50% the other. We have shown previously [32] that these crystals consist of a mosaic of blocks that contain similarly oriented virions, with the orientation differing between neighbouring blocks. When the orientations are averaged over the entire crystal volume, this distribution leads to additional (fourfold) symmetry within the data.…”

“…Data processing followed our standard procedures [5,37]. A mis-packing of the G67 crystals [32] resulted in the data possessing higher symmetry than is physically possible for virions packed in a unit cell of these dimensions. Thus, processing the data as space group 1432 gave Rmerge values equivalent to those seen for processing the 0 1 K data as space group 123 (Table 2), although this mis-packing results in a twofold loss of information.…”

Structure-based energetics of protein interfaces guides foot-and-mouth disease virus vaccine design

“…SAT2 crystals did not diffract to high resolution, however structures of the mutant A22 empty capsid and mutant O1M virus were solved at 2.4Å and 3.5Å resolution, respectively, using in situ room temperature X-ray crystallography17, 31. The O1M crystals were merohedrally twinned and a protocol was developed to de-convolute the twinned reflections32 (HMG, unpublished). Refinement using strict non-crystallographic symmetry and real-space averaging gave reliable maps and models for both structures (Table 2).…”

Analysis and characterization of data from twinned crystals

“…All these operators can be considered as a rotation about some axis de®ned as the twin axis. Extra complexities in the analysis are introduced when this axis is parallel to some axis of non-crystallographic symmetry (see, for example, Lea & Stuart, 1995).…”