Influenza virus hemagglutinin stem domain (HA stem)

The hemagglutinin stem domain is the lower structural portion (stalk) of the hemagglutinin glycoprotein found on the surface of influenza virions. Whereas the head (globe) domain mediates sialic acid receptor binding, the stem is responsible for mediating the conformational changes and membrane fusion events that allow viral entry into host cells after endocytosis. The stem domain contains highly conserved amino acid sequences and structural motifs, making it an attractive target for broad-spectrum influenza therapeutics and "universal vaccine" design, capable of eliciting broadly neutralizing antibodies effective against diverse influenza subtypes. Antibodies binding to the stem block membrane fusion, either directly or through immune effector mechanisms such as antibody-dependent cellular cytotoxicity and complement activation; experimental stem-only immunogens and monoclonal antibodies targeting the stem show broad protective efficacy in animal models and early clinical studies. Major challenges include overcoming immunodominance of the head domain and ensuring proper presentation and stability of the stem for effective vaccine design. This domain does not have a direct "receptor" function but is classified as a membrane fusion protein with critical roles in viral infectivity.

Other names

Hemagglutinin stalk domainHA stemHA2 (hemagglutinin subunit 2)Stalk region of hemagglutinin

Inhibition of viral membrane fusion by stabilizing prefusion conformation of HA stem; Antibody-dependent cellular cytotoxicity and complement-dependent lysis mediated by stem-targeting antibodies; Neutralization of viral infectivity by blocking conformational changes needed for fusion.