Enrichment of Phosphatidylethanolamine in Viral Replication Compartments via Co-opting the Endosomal Rab5 Small GTPase by a Positive-Strand RNA Virus.

Kai Xu,Peter D Nagy,Felix Rey

doi:10.1371/journal.pbio.2000128

Abstract

Positive-strand RNA viruses build extensive membranous replication compartments to support replication and protect the virus from antiviral responses by the host. These viruses require host factors and various lipids to form viral replication complexes (VRCs). The VRCs built by Tomato bushy stunt virus (TBSV) are enriched with phosphatidylethanolamine (PE) through a previously unknown pathway. To unravel the mechanism of PE enrichment within the TBSV replication compartment, in this paper, the authors demonstrate that TBSV co-opts the guanosine triphosphate (GTP)-bound active form of the endosomal Rab5 small GTPase via direct interaction with the viral replication protein. Deletion of Rab5 orthologs in a yeast model host or expression of dominant negative mutants of plant Rab5 greatly decreases TBSV replication and prevents the redistribution of PE to the sites of viral replication. We also show that enrichment of PE in the viral replication compartment is assisted by actin filaments. Interestingly, the closely related Carnation Italian ringspot virus, which replicates on the boundary membrane of mitochondria, uses a similar strategy to the peroxisomal TBSV to hijack the Rab5-positive endosomes into the viral replication compartments. Altogether, usurping the GTP-Rab5–positive endosomes allows TBSV to build a PE-enriched viral replication compartment, which is needed to support peak-level replication. Thus, the Rab family of small GTPases includes critical host factors assisting VRC assembly and genesis of the viral replication compartment.

Highlights

All RNA viruses with positive-strand genomes replicate in close association with subcellular membranes in plant or animal cells
The authors show that one of the two Tomato bushy stunt virus (TBSV) replication proteins interacts with the guanosine
Triphosphate (GTP)-bound Rab5 small GTPase, which allows the virus to take advantage of phosphatidylethanolamine (PE)-rich endosomes to build viral replication compartments consisting of peroxisomes

Summary

Introduction

All RNA viruses with positive-strand genomes replicate in close association with subcellular membranes in plant or animal cells. The virus-induced membranous structures representing the viral replication compartment help sequester viral proteins, viral RNAs, and co-opted host factors in confined areas for efficient viral replication complex (VRC) assembly and robust viral RNA replication, while protecting the viral RNA from cellular defense mechanisms. Current virology research is aimed at gaining deeper insights into the formation of viral replication compartments (frequently called replication organelles), which depends on interaction of viral replication proteins with subcellular membranes, lipids, and various co-opted host factors. Tomato bushy stunt virus (TBSV) usurps cellular membrane remodeling proteins, including the endosomal sorting complex required for transport (ESCRT) machinery [3,4,5], sterols, and phospholipids, to induce an elaborate membranous replication compartment harboring numerous vesicle-like structures in peroxisomal boundary membranes that support robust tombusvirus replication in a protective microenvironment [6]

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Conclusion