The capsid of HIV is a conical fullerene shell that comprises approximately 250 hexamers (orange) and exactly 12 pentamers (gold) of the viral CA protein. In the new study, the researchers determined X-ray crystal structures of these building blocks, which enabled modeling of the complete capsid at atomic resolution. The continuously varying lattice curvature in the fullerene cone can be explained simply by two rigid body rotations around two assembly interfaces of CA. (Graphics by Owen Pornillos, Barbie Ganser-Pornillos, Kelly Dryden, and Mark Yeager.)