Specifically, the HBV capsid, which is the protein shell that surrounds the virus's genetic material, is composed of a single type of protein called the HBcAg (Hepatitis B core antigen).

However, it's important to note that while HBV's capsid is made of just one type of protein, the entire virus structure is more complex and includes other proteins like the HBsAg (Hepatitis B surface antigen).