Unraveling the Structure of Viral Replication Complexes at Super-Resolution

Abstract

During infection, many RNA viruses produce characteristic inclusion bodies that contain both viral and host components. These structures were first described over a century ago and originally termed “X-bodies,” as their function was not immediately appreciated. Whilst some inclusion bodies may represent cytopathic by-products of viral protein over-accumulation, X-bodies have emerged as virus “factories,” quasi-organelles that coordinate diverse viral infection processes such as replication, protein expression, evasion of host defenses, virion assembly, and intercellular transport. Accordingly, they are now generally referred to as viral replication complexes (VRCs). We previously used confocal fluorescence microscopy to unravel the complex structure of X-bodies produced by Potato virus X (PVX). Here we used 3D-structured illumination (3D-SIM) super-resolution microscopy to map the PVX X-body at a finer scale. We identify a previously unrecognized membrane structure induced by the PVX “triple gene block” (TGB) proteins, providing new insights into the complex interplay between virus and host within the X-body.

Superresolution imaging of viral protein trafficking

“…For example, RNA viruses often induce the formation of punctate structures in the cytoplasm which have been described as “X-bodies” or replication “factories,” “organelles,” or “complexes.” Using 3D-SIM, Linnik and colleagues [89] followed up on previous confocal microscopy studies of potato virus X (PVX) induced X-bodies to more finely map the relative localizations of PVX proteins necessary for virus movement. The coat protein (CP), triple gene block (TGB) proteins, TGB1, TGB2, and TGB3 were imaged together or separately using intracellular markers.…”

Replication of Plant Viruses

“…The structure of replication complexes has been studied at super-resolution by Linnik et al (2013). These are not bounded by a clearly defined membrane but usually include some endoplasmic reticulum (ER) and ribosomes.…”

“…PVX replication complexes have been studied at "super-resolution" using 3D-structured illumination superresolution microscopy (Figure 7.18) (Linnik et al, 2013). They identified a previously unrecognized membrane structure induced by the PVX triple gene block proteins.…”

“…The triple gene block 1 (TGB1) "beaded sheets" (purple) are localized in the center of the X body. From Linnik et al (2013) with permission of the publishers. Host ER (green) is remodeled into arrays of small membrane hoops by TGB2 which are wrapped around the TGB1 aggregates within the X body.…”

e-Book on plant virus infection—a cell biology perspective

“…Linnik et al (2013) contribute a research article on how three-dimensional structured illumination microscopy (3D-SIM) can provide a novel high definition view of the potato virus X (PVX) factory architecture. They show previously unrecognized membrane structures induced by the PVX TGB proteins.…”