Proline-138 is essential for the assembly of hepatitis B virus core protein

In small RNA viruses, arm-like segments located at the N or C termini have been suggested as mediators in the assembly of the capsid proteins. In many cases the arms of several subunits converge at a common point (the symmetry axis). Recent advances in studies of the hepatitis B virus (HBV) core protein attest the convergence of the segments preceding the protamine region, around the symmetry axis, where five or six HBc protein subunits converge. We report a mutation study of the region that we have suggested forms an arm-like structure, which reveals that a single mutation, Pro-138 --> Gly, prevents the full-length HBV core protein self-assembling into particles.