Influenza Virus Adhesion to Living Cells Measured by Single Virus Force Spectroscopy (SVFS) and Force Probe MD Simulation

Abstract

Influenza virus belongs to a wide range of viruses that are enclosed in a lipid envelope. The major spike protein of the viral envelope hemagglutinin (HA) binds sialic acid (SA) residues of glycoproteins on the plasma membrane of the host cells. This represents the first step of infection and requires multiple simultaneous interactions since the affinity between one single HA-SA pair is very low (10-13 M-1).The binding interaction of influenza virus adhesion to living cells was probed by means of dynamic force spectroscopy and force probe molecular dynamics (MD) simulation. We applied three independent approaches to measure the unbinding force between influenza virus and a host cell membrane. Using optical tweezers and AFM based single molecule force spectroscopy we were able to characterize the binding energy on the single molecule level. Unbinding events where analysed and revealed a multimodal rupture force distribution which suggests sequential binding of multiple receptors. We determined the interacting force between hemagglutinin and its receptor sialic acid to be ∼10pN. Furthermore we used molecular dynamics simulation to gain information about the binding architecture and the sequence of the unbinding process. MD simulation allowed us a more detailed view of the energy landscape that governs the interaction between HA and its ligand.The combination of experimental and simulated force spectroscopy covers a very large force regime and provides information that could not be obtained with either one or the other method. The techniques are complementary and provide detailed insights of the molecular interactions involved in influenza virus attachment.