Force spectroscopy shows dynamic binding of influenza hemagglutinin and neuraminidase to sialic acid
V. Reiter-Scherer, J. L. Cuellar-Camacho, S. Bhatia, R. Haag, A. Herrmann, D. Lauster, J. P. Rabe – 2019
The Influenza A virus (IAV) infects target cells through multivalent interactions of its major spike proteins hemagglutinin (HA) and neuraminidase (NA) with the cellular receptor sialic acid (SA). HA is known to mediate the attachment of the virion to the cell, while NA enables the release of newly formed virions by cleaving SA from the cell. Since both proteins target the same receptor but have antagonistic functions, virus infection depends on a properly tuned balance of the kinetics of HA and NA activities for viral entry to and release from the host cell. Here dynamic single molecule force spectroscopy (SMFS), based on scanning force microscopy (SFM), was employed to determine these bond specific kinetics, characterized by the off-rate koff, rupture length xβ and on-rate kon, as well as the related free energy barrier ΔG and the dissociation constant KD. Measurements were conducted using surface immobilized HA and NA of the IAV strain A/California/04/2009 (H1N1), and a novel synthetic SA-displaying receptor for functionalization of the force probe. SMFS at force loading rates between 100 pN/s to 50,000 pN/s revealed most probable rupture forces of the protein-SA bond in the range of 10 pN to 100 pN. Using an extension of the widely applied Bell-Evans formalism by Friddle, De Yoreo and coworkers, it is shown that HA features a smaller xβ, a larger koff and a smaller ΔG than NA. Measurements of the binding probability at increasing contact time between the SFM force probe and the surface allow an estimation of KD, which is found to be three times as large for HA than for NA. This suggests a stronger interaction for NA-SA than for HA-SA. The biological implications in regard to virus binding to the host cell, and the release of new virions from the host cell are discussed.