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

PLoS Biol. 2020 Feb 10;18(2):e3000626. doi: 10.1371/journal.pbio.3000626. eCollection 2020 Feb.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Allosteric Regulation
  • Calcium / metabolism
  • Ebolavirus / chemistry
  • Ebolavirus / genetics
  • Ebolavirus / metabolism
  • Ebolavirus / physiology*
  • Fluorescence Resonance Energy Transfer
  • HEK293 Cells
  • Humans
  • Hydrogen-Ion Concentration
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Membrane Fusion*
  • Niemann-Pick C1 Protein
  • Polysaccharides / metabolism
  • Protein Binding
  • Protein Conformation
  • Protein Domains
  • Viral Envelope Proteins / chemistry*
  • Viral Envelope Proteins / genetics
  • Viral Envelope Proteins / metabolism*
  • Virus Internalization


  • Intracellular Signaling Peptides and Proteins
  • NPC1 protein, human
  • Niemann-Pick C1 Protein
  • Polysaccharides
  • Viral Envelope Proteins
  • envelope glycoprotein, Ebola virus
  • Calcium