Influenza hemagglutinin protein stem region (HA stem region)

The influenza hemagglutinin protein stem region is a highly conserved structural domain located at the base (proximal to the membrane) of the HA trimer, anchoring the globular head to the viral membrane. Hemagglutinin, the main surface glycoprotein of influenza A and B viruses, is critical for both viral attachment and membrane fusion during infection. The stem region, formed primarily by sequences from the HA2 subunit, harbors the molecular machinery necessary for fusion of the viral and cellular membranes after receptor-mediated endocytosis and exposure to low pH in the endosome[1][2][4]. This region is less variable than the head, making it the principal target for broadly neutralizing antibodies and the focus of universal influenza vaccine initiatives[1][10]. Broadly neutralizing antibodies, as well as small-molecule inhibitors and engineered binding proteins, can bind to the stem region and prevent the conformational changes required for fusion, thereby blocking viral entry and providing cross-strain protection[3][6][9][10]. Drugs directed at this region are under investigation, and the domain is increasingly recognized as a validated antiviral target.

Other names

Hemagglutinin stemHA stemInfluenza HA stemHemagglutinin stalkHA stalkInfluenza hemagglutinin stem

Inhibition of membrane fusion (by blocking structural rearrangement of the HA stem); Neutralization of viral infectivity by preventing conformational changes necessary for viral entry[3][6][10]; Promotion of antibody-dependent cell-mediated cytotoxicity and complement activation (for antibody drugs)[10]