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

Sophie L Winter, Gonen Golani, Fabio Lolicato, Melina Vallbracht, Keerthihan Thiyagarajah, Samy Sid Ahmed, Christian Lüchtenborg, Oliver T Fackler, Britta Brügger, Thomas Hoenen, Walter Nickel Ulrich S Schwarz, Petr Chlanda - Schaller Research Groups, University Hospital Heidelberg; BioQuant-Center for Quantitative Biology, Heidelberg University; Institute for Theoretical Physics, Heidelberg University, Heidelberg, Germany Heidelberg University Biochemistry Center, Department of Physics, University of Helsinki, Department of Infectious Diseases, University Hospital Heidelberg, German Centre for Infection Research (DZIF), Partner Site Heidelberg, Heidelberg, Germany Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Insitut, Greifswald-Insel Riems

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.

How Amira-Avizo Software is used

3D segmentation was performed using the Amira software and the implemented membrane enhancement filter. Membranes were automatically segmented using the Top-hat tool, and final segmentations were manually refined.