Grant: Travel Awards - Institute Community Support

Viral infection requires dedicated viral machinery for the water-soluble (hydrophilic) viral genetic material (genome) to exit its protein shell (capsid) and pass through the oily (hydrophobic) cell membrane. In the family of picornaviruses, which includes poliovirus, viral genome uncoating likely depends on the formation of pores within the cellular membrane by an assembly of viral proteins including VP4. Receptor mediated change in the virus capsid structure causes VP4 to rearrange from the inner surface of the capsid and be released to interact with the cellular membrane. VP4 is known to perforate synthetic oil droplets (liposomes), strongly suggesting its role in pore formation. Still, the molecular mechanisms by which VP4 binds viral genetic material (RNA) and protects the viral RNA genome through the cell's membrane remains poorly understood. Here we describe three dimensional imaging using electron microscopy of glass-like (vitreous), cryogenic poliovirus using a technique called cryo-electron tomography (cryo-ET) and subtomogram averaging to describe the sub-nanometre-scale structure of intact poliovirus bound to RNA in complex with VP4, which we refer to as polio-on-a-stick. Immuno-gold labelling demonstrates that the 'stick' of polio-on-a-stick is, in part, composed of VP4. This artificial assembly of VP4 and RNA exemplifies an intermediate step of viral genome exit. Understanding this structural arrangement of RNA, shielded by VP4, relative to the capsid, is an important step in describing the molecular mechanism by which the genome of picornaviruses traverses cellular membranes during infection.