Influenza A virus hemagglutinin (H1N1)pdm09 (HA)

Influenza A virus hemagglutinin (HA) is the primary surface glycoprotein of the H1N1 subtype that emerged during the 2009 pandemic, commonly referred to as A(H1N1)pdm09 [4, 16]. It is a homotrimeric class I fusion protein that plays a critical role in the initial stages of viral infection by mediating both host cell attachment and membrane fusion [3, 9]. The HA1 subunit contains the receptor-binding site that recognizes sialic acid residues on host respiratory epithelial cells, while the HA2 subunit facilitates the fusion of the viral and endosomal membranes under acidic conditions [6, 15]. Because HA is the major target for neutralizing antibodies, it is the central component of seasonal and pandemic influenza vaccines [12, 15]. Beyond vaccination, HA is a significant target for the development of novel antiviral therapeutics designed to overcome resistance to neuraminidase inhibitors. These include small-molecule fusion inhibitors like umifenovir (Arbidol), which stabilize the prefusion state of the protein, and broadly neutralizing monoclonal antibodies that target the highly conserved stem region of the HA molecule [1, 2, 5]. However, the therapeutic utility of HA-targeted agents is constantly challenged by the virus's high mutation rate. Antigenic drift in the globular head of HA allows the virus to evade host immunity and necessitates the frequent reformulation of vaccines, while specific mutations in the stem or receptor-binding domain can lead to drug resistance or altered host tropism [4, 11].

Other names

H1HAHemagglutininA(H1N1)pdm09 HA2009 pandemic H1N1 hemagglutininSwine-origin influenza A H1N1 hemagglutininpdm09 HA

Inhibition of viral membrane fusion by stabilizing the prefusion HA structure and blocking the conformational change required for fusion; neutralization of viral infectivity by blocking the receptor-binding site (RBS) on the HA1 subunit to prevent attachment to host cell sialic acid receptors [1, 2, 3, 7].