Influenza Virus Binds its Host Cell using Multiple Dynamic Interactions Revealed by Single Virus Force Spectroscopy and Force Probe Molecular Dynamics

Abstract

Influenza virus belongs to a wide range of enveloped viruses. Virus-host cell binding marks the first critical step of infection. Hence, forces involved in this process are essential. The major spike protein hemagglutinin (HA) binds sialic acid (SA) residues of glycoproteins and -lipids of the cell surface of host cells with dissociation constants in the millimolar range, indicating a multivalent binding mode. Here we characterized the attachment of influenza virus to host cell receptors using three independent approaches. Optical tweezers and atomic force microscopy based single molecule force spectroscopy revealed very low interaction forces in the order of ∼10-25 pN. Further, the observation of sequential unbinding events strongly suggests a multivalent binding mode between virus and cell membrane. Force probe molecular dynamics simulations reveal a variety of unbinding pathways that indicate a highly dynamic interaction between HA and its receptor allowing to rationalize influenza virus-cell binding quantitatively at molecular level. Simulations show that the receptor-binding domain of HA is very rigid and does not show any deformations during unbinding of the ligand, which does not argue for any cooperativity between HA monomers in binding. The observed unbinding pathways are diverse and contain zipper-like as well as all-or-none unbinding events. Notably, we did not find a clear preference for binding of the probed influenza strains to one of the cell lines differing in the structure of the SA receptors.Sieben et al. (2012) Proc Natl Acad Sci USA. 09:13626-13631