Protocol for purifying recombinant HBV capsids from HepG2 cells and comparative phosphorylation analysis by phosphate-affinity SDS-PAGE.

The hepatitis B virus (HBV) capsid protein (HBc or Cp) contains multiple phosphorylation sites that regulate distinct stages of the viral lifecycle. Here, we present a protocol for purifying HBV capsids by gradient ultracentrifugation and analyzing their phosphorylation states. We describe detailed steps for transfection, gradient purification, capsid detection, concentration, and phosphorylation-level profiling. This protocol provides a practical approach to assessing the global phosphorylation state of purified HBV capsids and can be adapted for comparative analyses across different capsid preparations. For complete details on the use and execution of this protocol, please refer to Bianchini et al.1.