Influenza Virus-Liposome Fusion Studies Using Fluorescence Dequenching and Cryo-electron Tomography

Methods Mol Biol. 2018:1836:261-279. doi: 10.1007/978-1-4939-8678-1_13.


Influenza virus enters host cells by fusion of viral and endosomal membranes mediated by the influenza hemagglutinin (HA). The pathway of HA-catalyzed fusion has been widely investigated in influenza virus membrane fusion with liposomes. In this chapter we describe methodology for studying the virus-liposome fusion system using a combination of fluorescence dequenching assays and cryo-electron tomography (cryo-ET). In particular, the fluorescence dequenching is used to monitor the efficiency of membrane fusion between whole influenza viruses labeled with a lipophilic dye (DiD) in the membrane and liposomes labeled with a water-soluble dye (sulforhodamine B). By simultaneously monitoring the two fluorescent signals, we can determine the relative time scales of liposomal content leakage or transfer vs. lipid merging. In addition, cryo-ET offers a means of imaging three-dimensional snapshots of different stages of virus-liposome fusion such as prefusion, fusion intermediates, and postfusion.

Keywords: Cryo-electron tomography; Fluorescence spectrometry; Influenza virus; Liposomes; Membrane fusion.

MeSH terms

  • Cryoelectron Microscopy*
  • Dynamic Light Scattering
  • Electron Microscope Tomography*
  • Fluorescent Antibody Technique*
  • Liposomes* / chemistry
  • Liposomes* / ultrastructure
  • Membrane Fusion*
  • Orthomyxoviridae / physiology*
  • Orthomyxoviridae / ultrastructure*


  • Liposomes