IFITM3 blocks influenza virus entry by sorting lipids and stabilizing hemifusion

Area of Science:

• Virology
• Cell Biology
• Biochemistry

Background:

• Interferon-induced transmembrane protein 3 (IFITM3) is known to inhibit viral entry.
• The precise molecular mechanisms by which IFITM3 exerts its antiviral effects remain largely undefined.
• IFITM3 localizes to the endosomal-lysosomal system and influences virus-cell membrane fusion.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying IFITM3-mediated viral entry inhibition.
• To investigate how IFITM3 affects the process of viral membrane fusion.
• To determine the role of IFITM3 in the context of influenza A virus infection.

Main Methods:

• In situ cryo-electron tomography to visualize viral fusion events.
• Analysis of lipid sorting at the cell membrane interface.
• Biochemical assays to assess fusion pore formation and hemifusion stability.
• Immunofluorescence to detect viral proteins and IFITM3 localization.

Main Results:

• IFITM3 induces local lipid sorting, concentrating lipids that disfavor membrane fusion at the hemifusion site.
• This lipid redistribution increases the energy barrier for fusion pore formation and prolongs hemifusion.
• Cryo-electron tomography captured IFITM3 arresting influenza A virus membrane fusion, with observed hemifusion diaphragms.
• Influenza hemagglutinin was found in a post-fusion conformation near hemifusion sites, indicating IFITM3 does not impede the fusion machinery itself.

Conclusions:

• IFITM3 utilizes lipid sorting to stabilize hemifusion intermediates, acting as a physical barrier to viral entry.
• This mechanism enhances viral degradation within lysosomes by preventing fusion pore formation.
• IFITM3 represents a novel antiviral target modulating host cell membrane properties to restrict viral infection.