Conformational changes in the Ebola virus membrane fusion machine induced by pH, Ca2+, and receptor binding.

• Main Authors: Dibyendu Kumar Das, Uriel Bulow, William E Diehl, Natasha D Durham, Fernando Senjobe, Kartik Chandran, Jeremy Luban, James B Munro
• Format: Article
• Language: English
• Published: Public Library of Science (PLoS) 2020-02-01
• Series: PLoS Biology
• Online Access: https://doi.org/10.1371/journal.pbio.3000626

The Ebola virus (EBOV) envelope glycoprotein (GP) is a membrane fusion machine required for virus entry into cells. Following endocytosis of EBOV, the GP1 domain is cleaved by cellular cathepsins in acidic endosomes, removing the glycan cap and exposing a binding site for the Niemann-Pick C1 (NPC1) receptor. NPC1 binding to cleaved GP1 is required for entry. How this interaction translates to GP2 domain-mediated fusion of viral and endosomal membranes is not known. Here, using a bulk fluorescence dequenching assay and single-molecule Förster resonance energy transfer (smFRET)-imaging, we found that acidic pH, Ca2+, and NPC1 binding synergistically induce conformational changes in GP2 and permit virus-liposome lipid mixing. Acidic pH and Ca2+ shifted the GP2 conformational equilibrium in favor of an intermediate state primed for NPC1 binding. Glycan cap cleavage on GP1 enabled GP2 to transition from a reversible intermediate to an irreversible conformation, suggestive of the postfusion 6-helix bundle; NPC1 binding further promoted transition to the irreversible conformation. Thus, the glycan cap of GP1 may allosterically protect against inactivation of EBOV by premature triggering of GP2.