A theory for viral capsid assembly around electrostatic cores

TL;DR

This paper develops equilibrium and kinetic theories to describe viral capsid assembly around charged cores, predicting threshold charge densities and assembly dynamics, with implications for nanoparticle and nucleic acid encapsulation.

Contribution

The paper introduces a theoretical framework combining electrostatic modeling and assembly kinetics to explain capsid formation around charged cores, aligning with experimental observations.

Findings

Capsid assembly occurs efficiently above a threshold charge density.

Light scatter intensity increases rapidly without a lag phase.

Discrepancies suggest metastable disordered states in experiments.

Abstract

We develop equilibrium and kinetic theories that describe the assembly of viral capsid proteins on a charged central core, as seen in recent experiments in which brome mosaic virus (BMV) capsids assemble around nanoparticles functionalized with polyelectrolyte. We model interactions between capsid proteins and nanoparticle surfaces as the interaction of polyelectrolyte brushes with opposite charge, using the nonlinear Poisson Boltzmann equation. The models predict that there is a threshold density of functionalized charge, above which capsids efficiently assemble around nanoparticles, and that light scatter intensity increases rapidly at early times, without the lag phase characteristic of empty capsid assembly. These predictions are consistent with, and enable interpretation of, preliminary experimental data. However, the models predict a stronger dependence of nanoparticle incorporation efficiency on functionalized charge density than measured in experiments, and do not completely capture a logarithmic growth phase seen in experimental light scatter. These discrepancies may suggest the presence of metastable disordered states in the experimental system. In addition to discussing future experiments for nanoparticle-capsid systems, we discuss broader implications for understanding assembly around charged cores such as nucleic acids.