Fig. 4

Cryo-EM structure of VACV D13 and its assembly. a Single particle cryo-EM 3D reconstruction of VACV scaffolding protein D13 in its native trimeric form (left) and the ribbon representation of its atomic model with a close-up view of N-terminal tail α-helix (right). b Single particle cryo-EM 3D reconstruction of D13 trimer doublet (left) and the ribbon representation of its atomic model with a close-up view of the inert-trimer interface where N-terminal tail α-helix is missing (right). The reconstructions and the models are colored according to domains in D13 monomer (blue: N-terminal jellyroll domain, red: C-terminal jellyroll domain, yellow: head domain, purple: N-terminal tail α-helix helix). c Spherical and d tubular assemblies produced in vitro under low salt condition when the N-terminal tail α-helix is dislocated or truncated, suggesting that the disposition of the helix triggers D13 self-assembly into IV scaffold. Scale bars are 5 nm in (a) and (b), and 100 nm in (c) and (d)