Methods and compositions for controlling assembly of viral proteins

A method for assembling a Hepatitis B Virus (HBV) core protein into a capsid structure, the method comprising:

• providing a solution comprising a modified HBV core protein and a first concentration of denaturing agent wherein the spike region of the modified HBV core protein comprises a cysteine residue;
• adding a drug to the solution;
• adding a reducing agent to the solution wherein the drug is added to the solution prior to the addition of the reducing agent:
• and
• diluting the first concentration of the denaturing agent to a second concentration after the addition of the reducing agent wherein the drug is added to the solution prior to diluting the denaturing agent,
• thereby to form an assembled capsid structure wherein the drug is encapsulated in the capsid structure.