Role of C-Terminal "Arms" in the Assembly and Stability of SV40 Polymorphs*

We study SV40 polymorphs by simulating the templated assembly process of VP1 pentamers. The simulations incorporate electrostatic effects and the connections formed between VP1 proteins by C-terminal flexible lateral units, termed here "arms". During assembly, VP1 pentamers connect to partial capsids before they bind to the template. The strength of these connections along with salt concentration can be manipulated leading to incomplete particles, T=1 particles, or aggregates of VP1 pentamers. In contrast to all other configurations, which are dynamic, the T=1 particles are static. The ability of VP1 pentamers to connect to other VP1 pentamers combined with the dynamic rearrangement of particles other than T=1 allows capsids to continue growing even when they are "pseudo-closed". The assembly mechanism described here is likely applicable to T=7 capsids.