Influenza hemagglutinin (HA) is a glycoprotein found on the surface of the influenzavirus. It is responsible for binding the virus to cells with sialic acid on their membranes, such as cells in the upper respiratory tract or erythrocytes. It is also responsible for the fusion of the viral envelope with the endosome membrane after the pH has been reduced. The name "hemagglutinin" comes from the protein's ability to cause red blood cells (erythrocytes) to clump together in vitro. HA has two functions. First, it allows the recognition of target vertebrate cells, accomplished through binding to these cells' sialic acid-containing receptors. Second, once bound it facilitates the entry of the viral genome into the target cells by causing the fusion of the host endosomal membrane with the viral membrane. H1N1 is a subtype of influenza virus A and the most common cause of influenza in humans.
Recombinant Influenza A H1N1 (A/California/04/2009(H1N1)) Hemagglutinin with his-tag produced in Sf9 Cell is a single, glycosylated polypeptide chain containing 520 amino acids. A fully biologically active molecule, HA-H1N1 has a molecular mass of ~66 kDa analyzed by reducing SDS-PAGE and is obtained by proprietary chromatographic techniques at GenScript.