Insights into Minor Group Rhinovirus Uncoating: The X-ray Structure of the HRV2 Empty Capsid

Damià Garriga,Angela Pickl-Herk,José R Castón,Núria Verdaguer,Daniel Luque,Jürgen Wruss,Dieter Blaas,Félix A Rey

doi:10.1371/journal.ppat.1002473

Abstract

Upon attachment to their respective receptor, human rhinoviruses (HRVs) are internalized into the host cell via different pathways but undergo similar structural changes. This ultimately results in the delivery of the viral RNA into the cytoplasm for replication. To improve our understanding of the conformational modifications associated with the release of the viral genome, we have determined the X-ray structure at 3.0 Å resolution of the end-stage of HRV2 uncoating, the empty capsid. The structure shows important conformational changes in the capsid protomer. In particular, a hinge movement around the hydrophobic pocket of VP1 allows a coordinated shift of VP2 and VP3. This overall displacement forces a reorganization of the inter-protomer interfaces, resulting in a particle expansion and in the opening of new channels in the capsid core. These new breaches in the capsid, opening one at the base of the canyon and the second at the particle two-fold axes, might act as gates for the externalization of the VP1 N-terminus and the extrusion of the viral RNA, respectively. The structural comparison between native and empty HRV2 particles unveils a number of pH-sensitive amino acid residues, conserved in rhinoviruses, which participate in the structural rearrangements involved in the uncoating process.

Highlights

A key step in the life cycle of viruses is the delivery of its genome into a compartment of the host cell appropriate for its replication
Much is known about their binding to cell receptors and their uptake into the host cell, the mechanism by which their genomic RNA leaves the capsid and arrives to the cytosol to initiate replication is poorly understood
The crystal structure of the HRV2 empty particle, representing the last stage of the uncoating process, unveils the structural rearrangements produced in the viral capsid during the externalization of the VP1 N-terminus and the delivery of the genomic RNA

Summary

Introduction

A key step in the life cycle of viruses is the delivery of its genome into a compartment of the host cell appropriate for its replication. This involves the recognition of specific cell surface receptors by the viral capsid and the passage of the genome across at least one membrane barrier. Enveloped viruses achieve this by fusing with cellular membranes. While crystallographic structures of various picornaviruses showed that VP4 and the N-terminus of VP1 line the interior of the capsid, biochemical experiments revealed that these peptides can be transiently exposed, demonstrating that the virions are highly dynamic and temporarily externalize otherwise internal structures via ‘breathing’ [3,4]

Methods

Results

Discussion

Conclusion