Revealing the evolution towards complex N-glycan specificities of human H1 influenza A viruses.

Influenza virus infection remains a threat to human health since viral hemagglutinins are constantly drifting, escaping infec-tion and vaccine-induced antibody responses. During antigenic drift H3 hemagglutinins have evolved to recognize a2,6 sialylated branched N-glycans with long glycan chains with at least three N-acetyllactosamine units (tri-LacNAc). In this work, we combined glycan arrays and tissue binding analyses with NMR experiments to characterize the interaction of a family of H1 variants, including the one responsible for the last pandemic outbreak. We also analyzed one H6 to understand if the preference for tri-LacNAc motifs is a general trend in recent zoonotic human-type receptor binding adapted viruses. In addition, we developed a new NMR approach to perform competition experiments between glycans with similar compositions and different lengths. Pandemic H1 viruses differ from previous seasonal H1 viruses by a strict preference for a minimum of di-LacNAc structural motif that are in turn present on the ferret upper respiratory tract.