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Nature. 2019 Jan;565(7739):377-381. doi: 10.1038/s41586-018-0852-1. Epub 2019 Jan 9.

Calicivirus VP2 forms a portal-like assembly following receptor engagement.

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Medical Research Council University of Glasgow Centre for Virus Research, Glasgow, UK.
Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, UK.
CRUK Beatson Institute, Glasgow, UK.
School of Life Sciences, University of Glasgow, Glasgow, UK.
Division of Virology, Department of Pathology, University of Cambridge, Cambridge, UK.
Medical Research Council University of Glasgow Centre for Virus Research, Glasgow, UK.


To initiate infection, many viruses enter their host cells by triggering endocytosis following receptor engagement. However, the mechanisms by which non-enveloped viruses escape the endosome are poorly understood. Here we present near-atomic-resolution cryo-electron microscopy structures for feline calicivirus both undecorated and labelled with a soluble fragment of its cellular receptor, feline junctional adhesion molecule A. We show that VP2, a minor capsid protein encoded by all caliciviruses1,2, forms a large portal-like assembly at a unique three-fold axis of symmetry, following receptor engagement. This assembly-which was not detected in undecorated virions-is formed of twelve copies of VP2, arranged with their hydrophobic N termini pointing away from the virion surface. Local rearrangement at the portal site leads to the opening of a pore in the capsid shell. We hypothesize that the portal-like assembly functions as a channel for the delivery of the calicivirus genome, through the endosomal membrane, into the cytoplasm of a host cell, thereby initiating infection. VP2 was previously known to be critical for the production of infectious virus3; our findings provide insights into its structure and function that advance our understanding of the Caliciviridae.


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