Influenza hemagglutinin trimer (HA trimer)

The **influenza hemagglutinin trimer** is a homotrimeric integral membrane glycoprotein found on the surface of influenza A and B viruses[1][7]. Each HA molecule is composed of three identical monomers, each initially synthesized as a single polypeptide (HA0), which is then cleaved into two subunits, HA1 (head) and HA2 (stem). The trimeric structure forms a cylindrical stalk that projects out from the viral envelope[1][5]. Hemagglutinin mediates both binding to sialic acid receptors on host cells and the subsequent fusion of viral and host membranes, a process triggered by acidification in the endosome after endocytosis[1][7]. There are multiple HA subtypes (H1–H16 in influenza A), and the protein is a dominant antigen for the host immune system, representing the principal target of neutralizing antibodies and vaccines[7]. The protein’s evolution through antigenic drift and shift underpins influenza pandemics and seasonal epidemics. The hemagglutinin trimer is the focus of both prophylactic (vaccine) and therapeutic (antibody and fusion inhibitor) drug development targeting influenza infection[7].

Other names

influenza hemagglutininHAhemagglutinin proteinHA trimeric glycoprotein

Inhibition of receptor binding (antibody blockade of HA head); Inhibition of membrane fusion (antibody stabilization of prefusion structure, or fusion inhibitors binding stem)