The Viroporin Activity of the Minor Structural Proteins VP2 and VP3 Is Required for SV40 Propagation

For nonenveloped viruses such as Simian Virus 40, the mechanism used to translocate viral components across membranes is poorly understood. Previous results indicated that the minor structural proteins, VP2 and VP3, might act as membrane proteins during infection. Here, purified VP2 and VP3 were found to form pores in host cell membranes. To identify possible membrane domains, individual hydrophobic domains from VP2 and VP3 were expressed in a model protein and tested for their ability to integrate into membranes. Several domains from the late proteins supported endoplasmic reticulum membrane insertion as transmembrane domains. Mutations in VP2 and VP3 were engineered that inhibited membrane insertion and pore formation. When these mutations were introduced into the viral genome, viral propagation was inhibited. This comprehensive approach revealed that the viroporin activity of VP2 and VP3 was inhibited by targeted disruptions of individual hydrophobic domains and the loss of membrane disruption activity impaired viral infection.