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. image Ebola viruses enter host cells via late endosomes and fuse their envelope with the endosomal membrane. Here, this step is shown to require the disassembly of the VP40 matrix as the first step of viral uncoating, which is triggered by the low endosomal pH. Low endosomal pH passively equilibrates across the endosomal membrane, independently of a dedicated viral ion channel Low pH inside the virus lumen disrupts electrostatic interactions between VP40 proteins and the viral membrane, leading to the disassembly of the VP40 matrix Disassembly of the VP40 matrix is pivotal in increasing the flexibility of the viral membrane and allowing membrane fusion Disassembly of the VP40 matrix precedes GP‐driven membrane fusion and release of the condensed nucleocapsid into the cytoplasm