Abstract
SummaryGlycoprotein B (gB) is a key component of the complex herpesvirus fusion machinery. We studied membrane interaction of two gB ectodomain forms and present an electron cryotomography structure of the gB-bilayer complex. The two forms differed in presence or absence of the membrane proximal region (MPR) but showed an overall similar trimeric shape. The presence of the MPR impeded interaction with liposomes. In contrast, the MPR-lacking form interacted efficiently with liposomes. Lateral interaction resulted in coat formation on the membranes. The structure revealed that interaction of gB with membranes was mediated by the fusion loops and limited to the outer membrane leaflet. The observed intrinsic propensity of gB to cluster on membranes indicates an additional role of gB in driving the fusion process forward beyond the transient fusion pore opening and subsequently leading to fusion pore expansion.
Highlights
Enveloped viruses enter cells by fusing their membrane with that of the host
We studied membrane interaction of two Glycoprotein B (gB) ectodomain forms and present an electron cryotomography structure of the gB-bilayer complex
The two forms differed in presence or absence of the membrane proximal region (MPR) but showed an overall similar trimeric shape
Summary
Enveloped viruses enter cells by fusing their membrane with that of the host. Dedicated proteins form fusion machinery mediating the merging of the two membranes. Upon activation that can be triggered by low pH, endosomal environment or protein-protein interaction with either a coreceptor in trans or a member of the complex fusion machinery in cis (i.e., on the same membrane side as the fusion mediating protein), hydrophobic fusion loops (FLs) are getting exposed and the protein adopts an intermediate extended conformation to reach the target membrane (Harrison, 2008) This transient extended intermediate conformation collapses, which brings the two membranes into proximity and, at the same time, induces curvature (Graham and Kozlov, 2010). In the final stage of fusion, the nascent fusion pore is been expanded to allow for full content mixing
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