Sequential conformational rearrangements in flavivirus membrane fusion.

Luke H Chao,Daryl E Klein,Stephen C Harrison,Aaron G Schmidt,Jennifer M Peña

doi:10.7554/elife.04389

Luke H Chao, Daryl E Klein + Show 3 more

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https://doi.org/10.7554/elife.04389

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Abstract

The West Nile Virus (WNV) envelope protein, E, promotes membrane fusion during viral cell entry by undergoing a low-pH triggered conformational reorganization. We have examined the mechanism of WNV fusion and sought evidence for potential intermediates during the conformational transition by following hemifusion of WNV virus-like particles (VLPs) in a single particle format. We have introduced specific mutations into E, to relate their influence on fusion kinetics to structural features of the protein. At the level of individual E subunits, trimer formation and membrane engagement of the threefold clustered fusion loops are rate-limiting. Hemifusion requires at least two adjacent trimers. Simulation of the kinetics indicates that availability of competent monomers within the contact zone between virus and target membrane makes trimerization a bottleneck in hemifusion. We discuss the implications of the model we have derived for mechanisms of membrane fusion in other contexts.

Highlights

Cell entry of enveloped viruses requires membrane fusion, catalyzed by a viral surface protein
We have studied the kinetics of West Nile Virus (WNV) membrane fusion, in a single-particle format developed previously to analyze influenza virus fusion (Floyd et al, 2008) (Figure 1C)
WNV virus-like particles (VLPs) were prepared as described in Methods

Summary

Introduction

Cell entry of enveloped viruses requires membrane fusion, catalyzed by a viral surface protein. The fusion protein of flaviviruses—the group that includes yellow fever (YFV), West Nile (WNV), dengue (DV), and tick-borne encephalitis (TBEV) viruses—is the envelope protein (E), which becomes fusogenic when exposed to reduced pH in an endosome (Allison et al, 1995; van der Schaar et al, 2007) This step merges viral and endosomal membranes and releases the viral genome into the cytosol. Modeling and experiment suggest that hydration-force repulsion occurs when two bilayers approach more closely than 15–20 Å Fusion proteins such as E reduce this barrier by inducing the distortion needed to form a hemifusion stalk—the short-lived intermediate that resolves to form a pore. They do so through a series of membrane-coupled conformational rearrangements (Harrison, 2008)

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Conclusion