The structures of a naturally empty cowpea mosaic virus particle and its genome-containing counterpart by cryo-electron microscopy

Emma L Hesketh,Yulia Meshcheriakova,Rebecca F Thompson,George P Lomonossoff,Neil A Ranson

doi:10.1038/s41598-017-00533-w

Abstract

Cowpea mosaic virus (CPMV) is a picorna-like plant virus. As well as an intrinsic interest in CPMV as a plant pathogen, CPMV is of major interest in biotechnology applications such as nanotechnology. Here, we report high resolution cryo electron microscopy (cryo-EM) maps of wild type CPMV containing RNA-2, and of naturally-formed empty CPMV capsids. The resolution of these structures is sufficient to visualise large amino acids. We have refined an atomic model for each map and identified an essential amino acid involved in genome encapsidation. This work has furthered our knowledge of Picornavirales genome encapsidation and will assist further work in the development of CPMV as a biotechnological tool.

Highlights

Cowpea mosaic virus (CPMV) is a plant-infecting member of the order Picornavirales, with a relatively simple, non-enveloped capsid that has been extensively studied
CPMV has an icosahedral capsid structure, which is ~30 nm in diameter and is formed from 60 copies each of a Large (L) and Small (S) coat protein. These two coat proteins are processed from a single RNA-2-encoded precursor polyprotein (VP60) by the action of the 24 K viral proteinase which is encoded by RNA-1
The C terminal 24 amino acids of the S subunit are essential for viral assembly and genome encapsidation[6]; these amino acids are cleaved during the normal maturation of the virus[7] and so are missing from all Comovirus X-ray structures, with the last amino acid observed in the S subunit of CPMV being Lys1891

Summary

Introduction

Cowpea mosaic virus (CPMV) is a plant-infecting member of the order Picornavirales, with a relatively simple, non-enveloped capsid that has been extensively studied. The second major point of interest in the previous cryo-EM structures of CPMV, was the presence of additional density representing part of the 24 amino acid, C terminal extension to the S subunit in the eVLP structure. The cryo-EM structures are of sufficient resolution to visualise the individual amino acid side chains and both structures reveal differences between the CPMV particles.

Results

Conclusion