Structure of the Reovirus Membrane-Penetration Protein, μ1, in a Complex with Its Protector Protein, σ3

Cell entry by nonenveloped animal viruses requires membrane penetration without membrane fusion. The reovirus penetration agent is the outer-capsid protein, μ1. The structure of μ1, complexed with its “protector” protein, σ3, and the fit of this μ13σ33 heterohexameric complex into the cryoEM image of an intact virion, reveal molecular events essential for viral penetration. Autolytic cleavage divides μ1 into myristoylated μ1N and μ1C. A long hydrophobic pocket can receive the myristoyl group. Dissociation of μ1N, linked to a major conformational change of the entire μ1 trimer, must precede myristoyl-group insertion into the cellular membrane. A myristoyl switch, coupling exposure of the fatty acid chain, autolytic cleavage of μ1N, and long-range molecular rearrangement of μ1C, thus appears to be part of the penetration mechanism.