Figure 8. Model of the immature virion-like particle assembly.

The color scheme used for D13 trimers is the same as in Figure 1. The membrane is represented in blue and the nickel-lipids are represented as yellow crosses and spikes. (a) Attachment sites for the His₆-tag promote membrane association of D13 in vitro. This interaction appears to act as a surrogate of viral binding partner(s) embedded in the membrane such as the A17 protein. (b) Subsequently, D13 trimers dock onto the surface and form a honeycomb lattice. (c) The apparently continuous curvature of the honeycomb lattice results in a crescent-like formation. (d) This structure is eventually extended to form a spherical particle. Defects in the lattice are not depicted here but they are necessary to achieve a closed shell and were frequently observed on immature virions in previous studies [8]. (e) Because D13 trimers do not interact directly with the membrane, cleavage of the attachment anchor, such as the N-terminal region of A17, may be sufficient to induce the detachment of either single trimers or assembled D13 sheets from the enveloped particle.