Protein Interactions Regulate Virus Assembly and Replication

Abstract

Hepatitis B virus (HBV) capsids are metabolic compartments for reverse transcription. Capsids are constructed from 120 self-assembling core protein (Cp) dimers. Assembly of capsids is regulated by the protein-protein interactions at core protein interface. We hypothesize that the Cp interactions are tuned for virus replication not for capsid stability.To test this hypothesis we designed Cp mutants with different contact energies. The starting point for our design was the structure of HBV capsid bound to heteroaryldihydropyrimidines (HAPs), small antiviral molecules that accelerate capsid assembly and strengthen Cp association by binding to a hydrophobic pocket at the Cp interface. We created mutants that filled the HAP pocket with different sized hydrophobic amino acids (V124A, V124L, V124F and V124W). The biophysical assembly properties of these mutants correlated well with the substitution. There was a linear relationship between the change in buried surface area and capsid association energy with an estimated −9 cal/(mol A2).However, in cell culture, these mutants have pleiotropic effects on DNA replication. Only the wild type Cp supported maximal DNA production. Mutants with stronger or weaker association energy were destructive to virus replication. Together, these data support our hypothesis that capsid association is tuned for virus replication. The proper stability of the capsid ensures its biological role in virus life cycle.