Thermodynamic and Kinetic Modeling of Polymorphism in Viral Capsid Assembly

Polymorphism in viral capsids poses a key problem in statistical physics: understanding how identical protein subunits assemble into distinct, stable structures under identical conditions. One example is the hepatitis B virus (HBV), forming two capsid morphologies containing 90 or 120 protein dimers. Experiments show that their relative abundance depends sensitively on ionic strength. We developed a model that incorporates salt effects by modulating the intermolecular binding free energy, thereby tuning the thermodynamic stability landscape. We reproduce experimentally observed morphology ratios across salt concentrations. A complementary kinetic model captures the time-dependent evolution of the two capsid forms, linking energetics, stoichiometry, and assembly pathways to reveal general physical principles governing viral polymorphism.