The Ebola virus VP40 matrix layer undergoes endosomal disassembly essential for membrane fusion

Abstract

Ebola viruses (EBOVs) assemble into filamentous virions, whose shape and stability are determined by the matrix viral protein 40 (VP40). Virus entry into host cells occurs via membrane fusion in late endosomes; however, the mechanism of how the remarkably long virions undergo uncoating, including virion disassembly and nucleocapsid release into the cytosol, remains unknown. Here, we investigate the structural architecture of EBOVs entering host cells and discover that the VP40 matrix disassembles prior to membrane fusion. We reveal that VP40 disassembly is caused by the weakening of VP40-lipid interactions driven by low endosomal pH that equilibrates passively across the viral envelope without a dedicated ion channel. We further show that viral membrane fusion depends on VP40 matrix integrity, and its disassembly reduces the energy barrier for fusion stalk formation. Thus, pH-driven structural remodeling of the VP40 matrix acts as a molecular switch coupling viral matrix uncoating to membrane fusion during EBOV entry.

RNA to Rule Them All: Critical Steps in Lassa Virus Ribonucleoparticle Assembly and Recruitment

“…Unlike influenza viruses, arenaviruses do not have proton channels in their lipid envelope that actively acidify the virion upon endocytosis. However, it has recently been shown for LASV that protons passively cross the viral membrane, which leads to acidification of the virus interior prior to membrane fusion. , Similar observations have been reported for Ebola virus, where acidification of virions leads to viral matrix reorganization . Besides the pH-dependent NP–Z interaction, we observed that Z starts to oligomerize between pH 5 and 5.5.…”

“…32,33 Similar observations have been reported for Ebola virus, where acidification of virions leads to viral matrix reorganization. 62 Besides the pH-dependent NP−Z interaction, we observed that Z starts to oligomerize between pH 5 and 5.5. We hypothesize that stronger Z−Z interaction at low pH, as indicated by oligomerization, further reduces availability of Z for the low-affinity Z−NP interaction.…”

Fusogenic structural changes in arenavirus glycoproteins are associated with viroporin activity

“…This phenomenon may be even more widespread among viruses. Winter et al have recently reported that passive acidification of the Ebola virus interior induces profound structural changes in the virion including the dissociation of the VP40 matrix layer from the viral membrane [66]. Further studies are needed to define the molecular mechanism for arenavirus PVMP and its role in its role in the early steps of arenavirus infection.…”

Membrane Tension Inhibits Lipid Mixing by Increasing the Hemifusion Stalk Energy

“…The presence of the support significantly increases the tension-independent contribution to stalk energy, F 0 , since the stalk formation involves local membrane detachment from the support. 47 However, the tension-dependent term, F T , is not significantly affected; while a negligible amount of membrane is withdrawn from the supported membrane, almost double the amount is drawn from the free membrane, resulting in a similar ΔA. To estimate the correction, we assume that the stalk shape at the GUV side is unaffected by the bead support.…”

“…Moreover, our experimental setting allows us to set the tension in the GUV membrane but not in the bead, which acts as a tight membrane support. The presence of the support significantly increases the tension-independent contribution to stalk energy, F 0 , since the stalk formation involves local membrane detachment from the support . However, the tension-dependent term, F T , is not significantly affected; while a negligible amount of membrane is withdrawn from the supported membrane, almost double the amount is drawn from the free membrane, resulting in a similar Δ A .…”