Fig. 1.
Cryo-EM reconstructions of RRV218 and RRV218/HS complex. (A) Shaded-surface representation of RRV218 mutant reconstruction map at 22 Å resolution, viewed along a two-fold axis. The open triangle highlights one asymmetric unit of the icosahedral structure, which is defined by the locations of the icosahedral two-, three-, and five-fold axes. The vertical dashed line identifies the position of a plane, 50 Å away from a central (equatorial) plane, corresponding to the density map sections shown in D and E. (B) Same as A but with the closest half computationally removed to expose internal features in the RRV218 reconstruction. Some axes of strict (2, 3, and 5) and quasi (q3) symmetry that lie in the central equatorial plane are identified. The lower-left quadrant highlights the approximate radial locations (tick marks along the vertical line) of the different viral components. These regions include the genome (r < 164 Å), the capsid (164 Å < r < 200 Å), the membrane bilayer (200 Å < r < 257 Å), and the glycoprotein shell (257 Å < r < 353 Å). (C) Hemispherical density projection (r = 254 Å) of the RRV218/HS minus RRV218 difference map (highest density features appear black). The triangulation net helps illustrate the presence of T = 4 quasi-symmetry and identifies virtual boundaries that separate the 80 trimeric glycoprotein spikes, twenty of which occur at the strict threefold axes and the remaining sixty of which occur at the quasi-three-fold positions. The punctate black dots correspond to the bound heparin molecules. About half of the 240 total heparin molecules are depicted in this hemisphere projection. Scale bar represents 200 Å for panels A–C. (D) Non-equatorial cross-section from the RRV218 reconstruction, extracted from the portion of the density map highlighted by the dashed line in A. This 1-pixel thick, density projection provides a slightly magnified, alternative view of the internal, multilayered RRV structure comparable to that shown in the top half of panel B. (E) Same as D but from the RRV218/HS minus RRV218 difference map. The most prominent and darkest features (arrow) all occur at a radius centered at 254 Å and are attributable to the presence of heparin molecules in the complex. Scale bar represents 200 Å for panels D and E.