Structure determination of enterovirus 71

Abstract

Enterovirus 71 is a picornavirus that causes hand, foot and mouth disease but may induce fatal neurological illness in infants and young children. Enterovirus 71 crystallized in a body-centered orthorhombic space group with two particles in general orientations in the crystallographic asymmetric unit. Determination of the particle orientations required that the locked rotation function excluded the twofold symmetry axes from the set of icosahedral symmetry operators. This avoided the occurrence of misleading high rotation-function values produced by the alignment of icosahedral and crystallographic twofold axes. Once the orientations and positions of the particles had been established, the structure was solved by molecular replacement and phase extension.

Figure 1

Rotation function of EV71 crystal diffraction data. Stereographic plots of (a) fivefold, (b) threefold and (c) twofold rotation functions were calculated using 18–13 Å resolution data and a 150 Å radius of integration. The plots are contoured starting from 0.5σ in 0.5σ increments. There are no obvious sets of icosahedrally related peaks. (d) Stereographic diagram showing the positions of icosahedral symmetry elements for all particles in the EV71 crystals. Fivefold axes are shown as red pentagons, threefold axes as green triangles and twofold axes as blue ovals.

Figure 2

Arrangement of the two crystallographically independent EV71 virions (red and blue) within the I2₁2₁2₁ crystal viewed along the c axis. The two particles are related by roughly a fourfold rotation, producing an approximate I4₁22 symmetry. Corresponding edges of each of the two icosahedrons are marked by arrows to highlight the approximate 90° rotation relating the two particles. The boundaries of the unit cell and the positions of symmetry elements in space group I2₁2₁2₁ are shown in black. The putative fourfold screw axis which replaces one of the twofold screw axes is shown in green.

Figure 3

Electron-density map of EV71 showing strands B and C on opposite sides of the jelly-roll β-barrel of VP1.

Figure 4

Comparison of the N-terminal arms of VP4 in (a) EV71 and (b) poliovirus 1. In each case one of the polypeptide chains is rainbow-coloured from blue at the N-terminus to yellow.