The hemagglutinin (HA) protein attaches viral particles to host cells by binding to sialic acid-containing receptors and induces viral particle internalization through clathrin-dependent endocytosis.HA also promotes an alternative clathrin- and caveolin-independent pathway for some virions.HA/Hemagglutinin Protein, H5N1 (ABW06108, HEK293, His) is the recombinant Virus-derived HA/Hemagglutinin protein, expressed by HEK293 , with C-His labeled tag.