Fig. 2: Design and characterization of the 240-subunit GI₄-F7 nanocage.

a, Schematic of pentasymmetron generation from I3-01 and the AAB heterotrimer. The A (cyan) subunits in the pentasymmetron retain the two-fold symmetric I3-01 nanocage interface, whereas the B (magenta) subunits are available for docking. b, Docking the pentasymmetron as a rigid body against CCC homotrimers (purple) yields 240-subunit, T = 4 assemblies. Translational and rotational degrees of freedom for the pentasymmetron and homotrimer components are indicated. c, A design model of GI₄-F7. d, Detail of the computationally designed interface between the B and C subunits of GI₄-F7 design model. e, Cryo-EM micrograph of assembled GI₄-F7 nanocages embedded in vitreous ice. Scale bar, 50 nm f, The 4.4 Å resolution density map of the entire GI₄-F7 nanocage. Scale bar, 49 nm. g, The 3.1 Å resolution density map from an asu obtained via symmetry-expansion and local refinement. Scale bar, 7.4 nm. h, Comparison of the cryo-EM structure derived from local refinement (grey ribbon) with the computational design model (coloured ribbons), aligned using a single copy of the asu. Arrows indicate rigid-body deviations of the pentasymmetron (cyan) and CCC homotrimer (purple). Int, interface. i,j, Detail of the rigid-body deviations from the design model at the B–C interface (i) and the A–A (I3-01) interface (j). In j, two neighbouring copies of the AAB heterotrimer from the full nanocage reconstruction and the design model were aligned.