Abstract

Human and avian influenza A viruses bind to sialic acid (Sia) receptors on cells as their primary receptors, and this results in endocytic uptake of the virus. While the role of Sia on glycoproteins and/or glycolipids for virus entry is crucial, the roles of the carrier proteins are still not well understood. Furthermore, it is still unclear how receptor binding leads to infection, including whether the receptor plays a structural or other roles beyond being a simple tether. To enable the investigation of the receptor binding and cell entry processes in a more controlled manner, we have designed a protein receptor for pandemic H1 influenza A viruses. The engineered receptor possesses the binding domains of an anti-HA antibody prepared as a single chain variable fragment (scFv) fused with the stalk, transmembrane and cytoplasmic sequences of the feline transferrin receptor type-1 (fTfR). When expressed in cells that lack efficient display of Sia due to a knockout of the Slc35A1gene which encodes for the Solute Carrier Family 35 transporter (SLC35A1), the anti-H1 receptor was displayed on the cell surface, bound virus or hemagglutinin proteins, and the virus was efficiently endocytosed into the cells. Infection occurred at similar levels to those seen after Sia reconstitution, and treatment with clathrin-mediated endocytosis (CME) inhibitors significantly reduced viral entry. IMPORTANCE.Influenza A viruses mostly circulate among avian reservoirs, and also can jump hosts to cause epidemics in mammals, including among humans. A key interaction of the viruses is with host cell Sia, which vary in chemical form, in their linkages within the oligosaccharide, and in the attachment to surface glycoproteins or glycolipids with different properties. Here we report a new method for examining the processes of receptor binding and uptake into cells during influenza A virus infection, by use of an engineered HA-binding membrane glycoprotein, where an antibody is used as the binding domain and the transferrin receptor uptake structures mediate efficient entry, which should allow us to test and manipulate the processes of cell binding, entry, and infection.