Intermediates in influenza induced membrane fusion

Area of Science:

• Virology
• Membrane Biology
• Structural Biology

Background:

• Influenza virus entry into host cells is crucial for infection.
• Hemagglutinin (HA) is the viral surface glycoprotein mediating membrane fusion.
• Understanding the HA-mediated fusion mechanism is key to developing antiviral strategies.

Purpose of the Study:

• To elucidate the sequential steps and conformational changes in hemagglutinin (HA) during influenza virus-host membrane fusion.
• To investigate the role of membrane contact site rearrangements in the fusion process.
• To propose a revised model for HA-mediated viral fusion.

Main Methods:

• Studying influenza virus-liposome fusion at reduced temperature (0°C) to slow and enhance fusion efficiency.
• Analyzing conformational changes in HA, including fusion peptide exposure and ectodomain trimer dissociation.
• Observing hydrophobic attachment, lag periods, membrane contact site rearrangements, and final bilayer merger.

Main Results:

• Fusion mechanism at 0°C and 37°C showed similar sequential steps.
• HA conformational changes exposed fusion peptides without immediate trimer top dissociation.
• Hydrophobic attachment was followed by a lag phase of membrane contact site rearrangements before bilayer merger.
• Final fusion was not pH-dependent, and efficient fusion at 0°C occurred without trimer top dissociation.

Conclusions:

• A revised model for HA-mediated fusion is proposed, highlighting sequential conformational changes in HA and membrane contact site dynamics.
• Efficient fusion at physiological temperatures may involve a transient HA conformation.
• The findings provide new insights into the molecular mechanisms of viral entry.