The role of the encapsulated cargo in microcompartment assembly
Fig 2
Snapshots from assembly trajectories of subunits with T = 3 preferred curvature.
(A) Small T = 3 shells (20 hexamers, 12 petamers) assembled without cargo at εHH = 2.6 and pentamer/hexamer stoichiometric ratio ρp/ρh = 0.5. Notice that the intermediate in the third frame contains a hexamer where a pentamer is required for icosahedral symmetry. This hexamer eventually dissociates. (B) One-step assembly with moderate cargo-cargo interaction strength, εCC = 1.5. A small nucleus of cargo and hexamer subunits forms, followed by simultaneous cargo coalescence, shell growth, and finally filling in of defects by pentamers subunits. The final structure has 68 hexamers, 12 pentamers, and 408 encapsulated cargo particles. Other parameters are hexamer-hexamer affinity εHH = 1.8, ratio of pentamer/hexamer affinity εPH/εHH = 1.3, and shell-cargo affinity εSC = 8.75, and ρp/ρh = 0.5. (C) Two-step assembly pathway for strong cargo-cargo affinity εCC = 1.65. Rapid cargo coalescence is followed by adsorption and assembly of shell subunits. The final structure has 167 hexamers, 12 pentamers, and 1520 encapsulated cargo particles. Other parameters are εHH = 1.8, εSC = 8.5, and ρp/ρh = 0.5. (D) Assembly and budding of shells from a cargo globule, for high pentamer/hexamer affinity ratio εPH/εHH = 2.0. Other parameters are εCC = 1.65, εHH = 1.8, εSC = 8.5 and ρp/ρh = 0.8. (We report energies in units of kBT throughout this article.) The shell bending modulus for all panels is κs = 10kBT. Animations corresponding to these trajectories are provided in S1, S2 and S3 Videos.