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Liposomes, Exosomes, and Virosomes: From Modeling Complex
Membrane Processes to Medical Diagnostics and Drug Delivery
Sunday Speaker Abstracts
10
Disentangling Viral Membrane Fusion from Receptor Binding Using Synthetic DNA-Lipid
Conjugates and a New Approach for Measuring Short-range Interactions in Membranes
Steven G. Boxer
1
, Robert Rawle
1,2
, Frank Moss
1
, Peter Kasson
2
.
1
Stanford University, Stanford, CA, USA,
2
University of Virginia, Charlottesville, VA, USA.
Enveloped viruses must bind to a receptor on the host membrane to initiate infection. Membrane
fusion is subsequently initiated by a conformational change in the viral fusion protein. We
present a method to disentangle the two processes of receptor binding and fusion using synthetic
DNA-lipid conjugates to bind enveloped viruses to target membranes in the absence of receptor.
We demonstrate this method by binding influenza virus to target vesicles and measuring the rates
of individual fusion events using fluorescence microscopy. Influenza fusion kinetics are found to
be independent of receptor binding. This approach should allow the study of viruses where
challenging receptor reconstitution has previously prevented single-virus fusion experiments
(e.g., HIV, Ebola and Zika).
The nanometer scale organization of the eukaryotic plasma membrane is presumed to be critical
for signaling, viral budding, and other membrane phenomena. We use secondary ion mass
spectrometry to probe the nanometer scale structure of supported lipid bilayers (SLBs) and
monolayers by taking advantage of the intermolecular recombination of ions to form diatomic
species that occurs in dynamic SIMS. As an example, we show that the efficiency of this atomic
recombination to form secondary 13C15N- ions depends on the distance between 13C and 15N
atoms installed on lipid head groups. Likewise we can measure recombination of labels on
opposite leaflets of a bilayer, putting an upper limit of about < 5 nm of the range of this method.
We refer to this method of measuring nanometer-scale distances between isotopically labeled
molecules as “a chemical ruler,” somewhat analogous to the use of FRET. While still in the
calibration phase, this method may provide information on lipid-lipid, lipid-protein and protein-
protein on a very short length scale.