Fig. 1

Cryo-EM density maps of HCIV-1 and HHIV-2 and MCPs. a Overall view of cryo-EM density maps of HCIV-1 (left) and HHIV-2 (right) color-coded by distance from the center (legend below). HCIV-1 is rendered to display the capsid shell (left-half) and the particle interior (right-half), genome in red and inner and outer membrane leaflets in yellow and yellow-lime (vertex complexes have been omitted, see Methods and Supplementary Figures 7 and 8). White-transparent hexagons on top of the capsid densities mark the capsomers (numbered in HCIV-1 Nos. 1–5) forming the icosahedral asymmetric unit (IAU); the white triangle and numbers on HHIV-2 surface mark a facet of the virion and the icosahedral symmetry axes, respectively. At the center, schematic of the capsomers organization with the three-tower capsomers (No. 1, light-yellow; No. 2, cyan; No. 3, pink), composed of three copies of MCP VP4 (blue circles) and three copies of MCP VP7 (light-gray circles) and with the two-tower capsomers (No. 4, light-green; No. 5, light-magenta; the latter sitting on the icosahedral two-fold axis) composed of two copies of VP4 and four copies of VP7; the five triangles composing the black pentagon represents the five copies of the penton protein plugging the vertices. Characters (A–X and a) identify each MCP subunit within the IAU and black short-lines joining the circles identify the VP7–VP4 heterodimers (see Fig. 2). b Cartoon representation of the HCIV-1 MCPs VP7 (left) with dashed-circle marking the loop with residues 149–154 [also marked in Fig. 2] and VP4 (right) with residue F149 colored in yellow and represented as stick; inset, stereoview of the region marked by a black rectangle with the VP4 atomic model (as stick and differently colored) fitted into the corresponding 3.7 Å resolution density map (blue mesh contoured at ∼3σ in COOT²⁶); some residues including F149 have been labeled