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Abstract
To achieve cell entry, many nonenveloped viruses must transform from a dormant to
a primed state. In contrast to the membrane fusion mechanism of enveloped viruses
(e.g., influenza virus), this membrane penetration mechanism is poorly understood.
Here, using single-particle cryo-electron microscopy, we report a 3.3 A structure
of the primed, infectious subvirion particle of aquareovirus. The density map reveals
side-chain densities of all types of amino acids (except glycine), enabling construction
of a full-atom model of the viral particle. Our structure and biochemical results
show that priming involves autocleavage of the membrane penetration protein and suggest
that Lys84 and Glu76 may facilitate this autocleavage in a nucleophilic attack. We
observe a myristoyl group, covalently linked to the N terminus of the penetration
protein and embedded in a hydrophobic pocket. These results suggest a well-orchestrated
process of nonenveloped virus entry involving autocleavage of the penetration protein
prior to exposure of its membrane-insertion finger.
2010 Elsevier Inc. All rights reserved.