FIG. 3.

T=1 SVP cryo-EM reconstruction. (A) Representative cryo-electron micrograph of T=1 SVP capsids. Bar = 200 Å. (B) Central section of the SVP map. Red arrows point to the densities (red circles) where the α4 helix was fitted. Bar = 25 Å. (C) Shaded surface representation of the complete SVP, at 7.2-Å resolution, with a highlighted VP2 trimer (white). Bar = 25 Å. (D) SVP 50-Å-thick slab. VP2 (PDB entry 2GSY) secondary structure elements are color coded by domain (red, P; blue, S; and green, B). (E) VP2 trimer X-ray model (PDB entry 2GSY) fitted into the corresponding density in the 7.2-Å cryo-EM map. The VP2 chain (452 residues) lacks 7 N-terminal and 11 C-terminal residues. The C-terminal α4 helices from adjacent VP2 chains that project towards the base of the threefold axis are not shown. Arrows indicate the cut directions to show P and S domain fits in panel F. (F) Transversal sections through P and S domains to visualize the fit of the two β-sheets. The map is contoured at 2σ above the mean density (i.e., less density is visible), showing the physical separation of the two β-sheets and a fictitious cavity (the hydrophobic core) between them.