Cryo-EM revealed that the HBV/G core protein was able to form T = 3 and T = 4 capsid structures similar to those formed by genotype A (Fig. 1) . Thus, we confirmed that the additional 12 N-terminal residues do not impair capsid formation. Furthermore, the insertion does not affect the basic structure of the core, other than presenting two additional regions of mass at the base of each of the spikes. Several groups have previously engineered N-terminal extensions to the HBcAg and found that this did not impair self-assembly of the expressed proteins into core-like particles [20, 21] . The majority of the HBV/G cores had T = 4 morphology, as previously reported in expressed core-like particles, and in cores isolated from patient specimens [22] .