Influenza hemagglutinin stem domain (HA stem)

The **influenza hemagglutinin stem domain** is a highly conserved, membrane-proximal region of the influenza virus hemagglutinin (HA) glycoprotein, essential for viral membrane fusion and entry into host cells[1][2][3][4]. Hemagglutinin is a class I fusion protein expressed as trimeric spikes on the viral envelope, with each monomer comprising a globular head (responsible for receptor binding) and a stem (or stalk) domain involved in mediating the conformational changes necessary for fusion following endosomal acidification[1][3]. The stem domain mainly consists of regions from both HA1 and HA2 subunits and anchors the HA trimer in the virion envelope, while also regulating the exposure of the fusion peptide[1][3][4]. Due to its relative conservation across influenza A subtypes, the HA stem is a key target for the development of "universal" influenza vaccines and broadly neutralizing antibodies that block the fusion step, in contrast to conventional antibodies that mainly recognize the variable HA head[2][3][4]. Stem-directed therapeutics aim to confer broad protection across seasonal and pandemic influenza strains, though antigenic drift and immune evasion remain ongoing challenges.

Other names

Hemagglutinin stemHA stemHemagglutinin stalkHA stalk

Inhibition of membrane fusion, Neutralization of viral entry