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Liposomes, Exosomes, and Virosomes: From Modeling Complex
Membrane Processes to Medical Diagnostics and Drug Delivery
Thursday Speaker Abstracts
42
Visualization and Sequencing of Membrane Remodeling Leading to Influenza Virus Fusion
Long Gui
1,2
, Jamie L. Ebner
1
, Alexander Mileant
2
,
Kelly K. Lee
1,2
.
1
University of Washington, Seattle, WA, USA,
2
University of Washington, Seattle, WA, USA.
Protein-mediated membrane fusion is an essential step in many fundamental biological events
including enveloped virus infection. The nature of protein and membrane intermediates and the
sequence of membrane remodeling during these essential processes remain poorly understood.
Here we used cryo-electron tomography (cryo-ET) to image the interplay between influenza
virus and vesicles with a range of lipid compositions. By following the population kinetics of
membrane fusion intermediates imaged by cryo-ET, we found that membrane remodeling
commenced with the hemagglutinin fusion protein spikes grappling to the target membrane,
followed by localized target membrane dimpling as local clusters of hemagglutinin started to
undergo conformational refolding. The local dimples then transitioned to extended, tightly
apposed contact zones where the two proximal membrane leaflets were in most cases
indistinguishable from each other, suggesting significant dehydration and possible intermingling
of the lipid head groups. Increasing the content of fusion-enhancing cholesterol or bis-
monoacylglycerophosphate in the target membrane, led to an increase in extended contact zone
formation. Interestingly, hemifused intermediates were found to be extremely rare in the
influenza virus fusion system studied here, most likely reflecting the instability of this state and
its rapid conversion to postfusion complexes, which increased in population over time. By
tracking the populations of fusion complexes over time, the architecture and sequence of
membrane reorganization leading to efficient enveloped virus fusion were thus resolved.