Features of reovirus outer capsid protein μ1 revealed by electron cryomicroscopy and image reconstruction of the virion at 7.0 Å resolution

Reovirus is a useful model for addressing the molecular basis of membrane penetration by one of the larger nonenveloped animal viruses. We now report the structure of the reovirus virion at 7.0 angstrom resolution as obtained by electron cryomicroscopy and three-dimensional image reconstruction. Several features of the myristoylated outer capsid protein mu 1, not seen in a previous X-ray crystal structure of the mu 1-sigma 3 heterohexamer, are evident in the virion. These features appear to be important for stabilizing the outer capsid, regulating the conformational changes in mu 1 that accompany perforation of target membranes, and contributing directly to membrane penetration during cell entry.