Disentangling Viral Entry Kinetics Using Lipid Bilayers Coating Silica Nanoparticles

Enveloped viruses infect cells via fusion between the viral envelope and a cellular membrane. This membrane fusion process is driven by viral proteins, but slow stochastic protein activation dominates fusion kinetics, making it challenging to probe the role of membrane mechanics in viral entry directly. We have used bilayer-coated silica nanoparticles to restrict the deformability of lipid membranes in a controllable manner. These bilayer-coated nanoparticles are then used in a single-particle fusion assay with infectious influenza virus. We observe that as we vary the free energy of membrane deformation by changing nanoparticle size, we obtain a corresponding response in fusion kinetics and apparent fusion protein stoichiometry. We thus directly measure the effect of membrane deformability on the free-energy barrier to membrane fusion by influenza, overcoming the masking effect of slow protein activation kinetics.