Ionic impact on viral capsid dimorphism

Polymorphism is commonly observed in many viruses during the spontaneous assembly of viral capsids. Among these, the hepatitis B virus (HBV) exhibits two structural variants that coexist stably both in vivo and in vitro. These variants differ in diameter and consist of 90 and 120 capsid subunits, respectively. Interestingly, experiments have shown that the relative prevalence of these variants can be manipulated by altering the concentration of cations in the assembly environment. We hypothesize that the cations modify the intermolecular binding energy between capsid proteins, resulting in changes in the prevalence of each variant. To test this hypothesis, we develop a mathematical model incorporating the concentration of salt via the Debye screening length, which adequately explains the equilibrium prevalence ratio of the large and small HBV variants.