Poliovirus RNA Is Released from the Capsid near a Twofold Symmetry Axis

Abstract

After recognizing and binding to its host cell, poliovirus (like other nonenveloped viruses) faces the challenge of translocating its genome across a cellular membrane and into the cytoplasm. To avoid entanglement with the capsid, the RNA must exit via a single site on the virion surface. However, the mechanism by which a single site is selected (from among 60 equivalents) is unknown; and until now, even its location on the virion surface has been controversial. To help to elucidate the mechanism of infection, we have used single-particle cryoelectron microscopy and tomography to reconstruct conformationally altered intermediates that are formed by the poliovirion at various stages of the poliovirus infection process. Recently, we reported icosahedrally symmetric structures for two forms of the end-state 80S empty capsid particle. Surprisingly, RNA was frequently visible near the capsid; and in a subset of the virions, RNA was seen on both the inside and outside of the capsid, caught in the act of exiting. To visualize RNA exiting, we have now determined asymmetric reconstructions from that subset, using both single-particle cryo-electron microscopy and cryo-electron tomographic methods, producing independent reconstructions at ϳ50-Å resolution. Contrary to predictions in the literature, the footprint of RNA on the capsid surface is located close to a viral 2-fold axis, covering a slot-shaped area of reduced density that is present in both of the symmetrized 80S reconstructions and which extends by about 20 Å away from the 2-fold axis toward each neighboring 5-fold axis.

Cross-neutralizing human anti-poliovirus antibodies bind the recognition site for cellular receptor

“…The pattern of A12 binding described in this communication seems to be similar to the binding of rhinovirus 14 antibodies. This may have implications for the mechanism of action of these antibodies, because it is believed that during poliovirus uncoating the RNA molecule is released from the capsid through the temporary umbilical connections that are formed between cellular membrane and the virion region located near the twofold axis of symmetry (18)(19)(20). This region would be shielded by a bivalent IgG molecule if its two Fab fragments are bound to canyons surrounding adjacent pentamers.…”

Cryo-EM study of slow bee paralysis virus at low pH reveals iflavirus genome release mechanism

“…There are functionally important differences between the two families as well as with the genome release mechanism of SBPV described here. The uncoating of enteroviruses from the family Picornaviridae is preceded by the formation of expanded A particles (19)(20)(21)23). The A particles contain two types of pores located at twofold and between twofold and fivefold symmetry axes of the capsids, have N termini of VP1 subunits exposed at the virion surface, and spontaneously release VP4 subunits (46,47).…”

“…Amphipathic sequences from the N termini of VP1 and myristoylated VP4 subunits interact with endosome membranes and enable the delivery of enterovirus genomes into the cell cytoplasm (25)(26)(27). It has been previously proposed that the enterovirus genome leaves the capsid via a pore located at a twofold icosahedral axis (19)(20)(21). The resulting empty capsids are conventionally referred to as B particles (19).…”

“…1073/pnas.1616562114/-/DCSupplemental. particle surface, and released VP4 subunits (19)(20)(21)(22)(23)(24). Amphipathic sequences from the N termini of VP1 and myristoylated VP4 subunits interact with endosome membranes and enable the delivery of enterovirus genomes into the cell cytoplasm (25)(26)(27).…”

Molecular Symmetry and Biological Activities of New Symmetrical Tris(2-aminoethyl)amine Derivatives

“…Two-fold and three-fold symmetrical macromolecular structures are common features in specialized biological functions. [2][3][4] Regarding the molecular symmetry, small symmetrical molecules with a C 2 -symmetrical or C 3 -symmetrical structure have often been found in various synthetic biologically active compounds. [5][6][7] In the course of our work on new antiviral compounds, we have presented a new class of antiviral candidates.…”