Disentangling Viral Membrane Fusion from Receptor Binding Using Synthetic DNA-Lipid Conjugates.

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, triggered by receptor binding, an environmental change, or both. Here, we present a strategy 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. This permits direct testing of whether receptor engagement affects the fusion mechanism as well as a comparison of fusion behavior across viruses with different receptor binding specificities. We demonstrate this approach by binding X-31 influenza virus to target vesicles and measuring the rates of individual pH-triggered lipid mixing events using fluorescence microscopy. Influenza lipid mixing kinetics are found to be independent of receptor binding, supporting the common yet previously unproven assumption that receptor binding does not produce any clustering or spatial rearrangement of viral hemagglutinin, which affects the rate-limiting step of pH-triggered fusion. This DNA-lipid tethering strategy should also allow the study of viruses where challenging receptor reconstitution has previously prevented single-virus fusion experiments.