Influenza A virus H1N1pdm09 hemagglutinin (HA)

The Influenza A virus H1N1pdm09 hemagglutinin (HA) is a major surface glycoprotein that forms a trimeric spike on the viral envelope, consisting of HA1 and HA2 subunits responsible for host cell receptor recognition and viral entry.[1][3][8] HA binds to sialic acid-terminated glycans on respiratory epithelial cells via its receptor-binding site (RBS), composed of structural elements like the 130 loop, 180 helix, and 220 loop, facilitating viral attachment.[2][3][5] Following endocytosis, low pH triggers conformational changes in the HA2 stalk, driving fusion of viral and endosomal membranes to release the viral genome.[1][8] Early 2009 pandemic strains showed unstable trimers due to weak monomer interfaces, but mutations like E374K in HA2 enhanced trimer stability, protease resistance, and viral fitness without altering receptor specificity.[1][2] HA antigenic evolution involves substitutions in sites like Sa (e.g., K166Q) and the RBS vicinity (e.g., S188T, S206T), enabling immune escape while balancing receptor avidity and specificity for human α2-6-linked sialic acids.[3][5] Coevolution with neuraminidase maintains replication balance.[5] As a key vaccine antigen, HA stability impacts recombinant vaccine production, with later strains yielding more robust trimers.[1][4] No direct small-molecule drugs target HA clinically, but its conserved structure supports broad monoclonal antibody and vaccine strategies against H1N1pdm09 infections.[3][6]

Other names

H1N1pdm09 HApH1N1 hemagglutininA(H1N1)pdm09 hemagglutinin