Polymorphism and Dynamics of the Hepatitis B Virus Capsid

Abstract

Virus capsid proteins spontaneously self-assemble into hollow shells under the right conditions driven by an interaction energy of the order of 10 kT, consisting of a short range attraction balanced by an electrostatic repulsion. In this regime of soft interactions it is subject to debate whether the properties of the assembly process are dominated by kinetics or by thermodynamics. Here we account for the observed virus capsid polymorphism of Hepatitis B both from the perspective of assembly rates and equilibrium energies by adding a curvature free energy term to the interaction potential. From these models we propose experiments that may conclusively distinguish between kinetically and thermodynamically governed polymorphism. In order to also adress the role of entropy to the assembly proces, we investigate the protein dynamics using NMR spectroscopy. We find indications for subunit exchange between dimer and capsid corroborating the notion of weak interaction enthalpy. Furthermore we obtained qualitative information on the global dynamics of the HBV capsid using the size dependence of cross-relaxation induced polarization transfer and we find that the C-terminal tail is the only region of the protein with flexibility on timescales of microseconds or faster.