Co-opted Oxysterol-Binding ORP and VAP Proteins Channel Sterols to RNA Virus Replication Sites via Membrane Contact Sites

Daniel Barajas,Peter D Nagy,Cristina Risco,Kai Xu,Federica Brandizzi,Isabel Fernández De Castro Martín,Zsuzsanna Sasvari,Aiming Wang

doi:10.1371/journal.ppat.1004388

Abstract

Viruses recruit cellular membranes and subvert cellular proteins involved in lipid biosynthesis to build viral replicase complexes and replication organelles. Among the lipids, sterols are important components of membranes, affecting the shape and curvature of membranes. In this paper, the tombusvirus replication protein is shown to co-opt cellular Oxysterol-binding protein related proteins (ORPs), whose deletion in yeast model host leads to decreased tombusvirus replication. In addition, tombusviruses also subvert Scs2p VAP protein to facilitate the formation of membrane contact sites (MCSs), where membranes are juxtaposed, likely channeling lipids to the replication sites. In all, these events result in redistribution and enrichment of sterols at the sites of viral replication in yeast and plant cells. Using in vitro viral replication assay with artificial vesicles, we show stimulation of tombusvirus replication by sterols. Thus, co-opting cellular ORP and VAP proteins to form MCSs serves the virus need to generate abundant sterol-rich membrane surfaces for tombusvirus replication.

Highlights

Plus-stranded (+)RNA viruses subvert various intracellular and organellar membranes to assemble viral replicase complexes (VRCs) consisting of viral replication proteins and co-opted host proteins and the viral RNAs in the infected cells [1,2,3,4,5,6]
Cellular proteins and cellular membranes are usurped by positive-stranded RNA viruses to assemble viral replicase complexes required for their replication
Tombusvirus replication greatly depends on sterols [47], which are distributed in cells via vesicle transfer and sterol-binding Oxysterolbinding protein related proteins (ORPs) proteins in a vesicle independent pathway [53,55]

Summary

Introduction

Plus-stranded (+)RNA viruses subvert various intracellular and organellar membranes to assemble viral replicase complexes (VRCs) consisting of viral replication proteins and co-opted host proteins and the viral RNAs in the infected cells [1,2,3,4,5,6]. Viral RdRps of many (+)RNA viruses interact with membranes and build functional VRCs in singlemembrane spherules and vesicle-like structures that have a narrow opening to the cytosol. The virus-induced VRCs and membranous structures gather all the replication factors into confined cytosolic areas, but importantly, they protect the fragile viral RNAs from degradation by host ribonucleases and help avoid recognition of viral components by the host antiviral surveillance system [6,19]. Assembly of the VRCs is an essential step during the replication of (+)RNA viruses that is absolutely dependent on cellular lipids and membranes in the infected cells

Methods

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Discussion

Conclusion