Multivalent and dynamic interactions of the influenza virus at lipid membrane interfaces

The surface of influenza viruses is decorated with two glycoproteins, hemagglutinin (HA) and neuraminidase (NA), that form the characteristic “spikes” and work together in host cell recognition. The receptor specificity of HA and NA is considered a key factor in the adaptation of the virus to different hosts. The receptors for both HA and NA are sialic acid-terminated glycans. NA can cleave the sialic acid from the glycan upon binding. A functional balance exists between the binding and cleaving functions of the two glycoproteins that keeps the virus-receptor interactions dynamic and imparts motility to the virus. A method is presented, called “multivalent affinity profiling”, to quantitatively assess the multivalent binding of influenza viruses on cell-mimicking surfaces through imaging of the virus’ superselectivity on receptor density gradients. The multivalent virus-surface binding has a threshold receptor density above which the binding becomes efficient, which is the hallmark of the multivalent nature of the binding process. The threshold receptor density is stable over time and varies barely with virus concentration, but increases nonlinearly with flow rate due to the shear force exerted on the virus particles. Multivalent affinity profiling was used to compare the binding of an influenza virus to avian and human-type receptors of different lengths. A theoretical model is presented to calculate the avidity, the number of HA-receptor interactions, and their average strength from the threshold receptor density. The influence of NA on the binding of influenza virus as a function of receptor density is studied by varying the concentration of NA inhibitor. With active NA, the virus has a higher avidity due to the contribution of NA to the binding, but the receptor-cleaving activity of NA lowers the receptor density. The virus binding is decreased overall but more strongly at low receptor densities, leading to an enhanced selectivity towards high initial receptor densities. The new insights in the binding of influenza may help to predict properties of emerging influenza strains as well as other viruses, and help the development of broad-spectrum antivirals and targeted anticancer treatments.