Mechanisms of viral capsid assembly around a polymer

TL;DR

This study uses lattice simulations to explore how polymer length influences viral capsid assembly efficiency, revealing an optimal length for assembly and mechanisms by which polymers enhance assembly rates.

Contribution

The paper introduces a lattice simulation model to analyze how polymer properties affect viral capsid assembly, highlighting an optimal polymer length and polymer-mediated rate enhancements.

Findings

Assembly is most efficient at an optimal polymer length proportional to capsid surface area.

Longer polymers tend to produce partial capsids with unpackaged tails or multiple capsids attached.

Polymers can increase subunit accretion rates by stabilizing addition and enhancing subunit flux.

Abstract

Capsids of many viruses assemble around nucleic acids or other polymers. Understanding how the properties of the packaged polymer affect the assembly process could promote biomedical efforts to prevent viral assembly or nanomaterials applications that exploit assembly. To this end, we simulate on a lattice the dynamical assembly of closed, hollow shells composed of several hundred to 1000 subunits, around a flexible polymer. We find that assembly is most efficient at an optimum polymer length that scales with the surface area of the capsid; significantly longer than optimal polymers often lead to partial-capsids with unpackaged polymer `tails' or a competition between multiple partial-capsids attached to a single polymer. These predictions can be tested with bulk experiments in which capsid proteins assemble around homopolymeric RNA or synthetic polyelectrolytes. We also find that the polymer can increase the net rate of subunit accretion to a growing capsid both by stabilizing the addition of new subunits and by enhancing the incoming flux of subunits; the effects of these processes may be distinguishable with experiments that monitor the assembly of individual capsids.