Primed for Discovery: Atomic-Resolution Cryo-EM Structure of a Reovirus Entry Intermediate

A recently solved structure of the aquareovirus virion (Zhang, X; Jin, L.; Fang, Q; Hui, W.H.; Zhou Z.H. 3.3 Å Cryo-EM Structure of a Nonenveloped Virus Reveals a Priming Mechanism for Cell Entry. Cell2010, 141, 472-482 [1]) provides new insights into the order of entry events, as well as confirming and refining several aspects of the entry mechanism, for aquareovirus and the related orthoreovirus. In particular, the structure provides evidence of a defined order for the progressive proteolytic cleavages of myristoylated penetration protein VP5 that prime the virion for membrane penetration. These observations reinforce the concept that, much like enveloped viruses, nonenveloped virions often undergo priming events that lead to a meta-stable state, preparing the virus for membrane penetration under the appropriate circumstances. In addition, this and other recent studies highlight the increasing power of electron cryomicroscopy to analyze large, geometrically regular structures, such as icosahedral viruses, at atomic resolution.