Figure 4. Structure of the inner P1 shell.

(a) Close-ups of the atomic models for the φ6 P1_A (top) and P1_B (bottom) subunits and corresponding density (mesh). (b) Atomic model of the asymmetric P1 dimer. The two subunits and the N- and C-termini are labelled. (c) Close-up of the density map. Icosahedral symmetry axes are labelled with an ellipse (two-fold), a triangle (three-fold) and a pentagon (five-fold). (d) Same view as in c but a rough molecular surface is shown for clarity and one P1 dimer is shown as a ribbon. P1_A is blue, P1_B is red, and density assigned to P4 C-terminal part is dark blue. (e) Atomic model for the P4 C-terminal part (R292–L332) and the corresponding density (mesh) are shown. (f) Close-up of the area indicated in e showing the 324-ProArgArg-326 motif that allowed assignment of this density to P4. See also Supplementary Fig. 4 and Supplementary Movie 1.