Enterovirus particles expel capsid pentamers to enable genome release

Abstract

Viruses from the genus Enterovirus are important human pathogens. Receptor binding or exposure to acidic pH in endosomes converts enterovirus particles to an activated state that is required for genome release. However, the mechanism of enterovirus uncoating is not well understood. Here, we use cryo-electron microscopy to visualize virions of human echovirus 18 in the process of genome release. We discover that the exit of the RNA from the particle of echovirus 18 results in a loss of one, two, or three adjacent capsid-protein pentamers. The opening in the capsid, which is more than 120 Å in diameter, enables the release of the genome without the need to unwind its putative double-stranded RNA segments. We also detect capsids lacking pentamers during genome release from echovirus 30. Thus, our findings uncover a mechanism of enterovirus genome release that could become target for antiviral drugs.

Capsid Structure of a Marine Algal Virus of the Order Picornavirales

“…These viruses utilize a variety of receptors, such as immunoglobulins, integrins and sialic acids, to facilitate binding to cell surfaces, which results in endocytosis. Receptor binding and/or pH changes in the endosomal system lead to genome release, which was recently shown to be facilitated by the loss of capsid-protein pentamers (65). The hydrophobic N terminus of VP1 anchors the viron to the endosomal membrane, and the minor VP4 protein forms hexameric membrane pores (64,66).…”

Structures of Echovirus 30 in complex with its receptors inform a rational prediction for enterovirus receptor usage

“…Currently, there are no approved vaccines or antiviral therapies available for treating infections caused by echoviruses. Although capsid structures for many EVs have been studied extensively [6][7][8][9][10][11][12][13][14][15][16][17][18][19] , large gaps in our knowledge concerning determinants of specificity between the serotypes/subgroups and characteristics for receptor usage in EV-Bs still exist. Therefore, an in-depth understanding of E30 structural features and receptor recognition mechanisms should be useful in providing guidance for the rational drug design against EV-Bs infections.…”

The In Silico Prediction of Hotspot Residues that Contribute to the Structural Stability of Subunit Interfaces of a Picornavirus Capsid

“…Residues K256 and R264 corresponding to K241 and R249 were previously found to be vital for EV-71 replication [20], while hotspots Y124, N204, F246 and R249 (VP1) are conserved with energetically important residues that were predicted to contribute to the stability of intraprotomer interfaces in the enteroviruses [36]. Several studies have recently speculated that interactions between VP4, the N-termini of VP1-3 and viral RNA also influence the dynamics of capsid stability [51,[58][59][60][61]. In this study, protein-RNA interactions were not analysed; however, it is interesting to note that hotspot K241 (VP1) corresponds to residue R202 in human parechovirus 3 (HPeV-3) that was previously reported to interact with the viral genome [51].…”

“…It is generally accepted that the interfaces between pentamer subunits are major sites of structural rearrangement during capsid uncoating. For example, studies have widely documented the formation of pores at these interfaces [67][68][69][70][71][72][73] or the loss of one or more pentamer subunit(s) [53,58,74,75] upon exposure of the picornavirus capsid to denaturing conditions. To identify the hotspot residues that are critical to the binding specificity and stability of the pentamer interfaces, complexes of two opposing protomers at the two-fold axis and two adjacent protomers at the three-fold axis were analysed.…”