Icosahedral capsid formation by capsomer subunits and a semiflexible polyion

The role of the genome in the assembly of icosahedral viral capsids has been investigated by molecular dynamics simulation of a coarse-grained model, in which the capsomers carry explicit charges and the polynucleic acid is represented by a bead-spring chain. The co-assembly process was contrasted with the self-assembly of uncharged capsomers. In the co-assembly, the capsomers first associated to the polyion and then rearrange into a capsid, whereas the self-assembly proceeded through a spontaneous nucleation and growth of partial capsids. The polyion backbone stiffness was found to have a significant effect on the co-assembly process; polyions of intermediate flexibility gave the fastest and most faithful assembly process. Addition of a small amount of monovalent salt also improved both speed and fidelity of the co-assembly process.