The HA/hemagglutinin protein binds to cell surface receptors, allowing viral particles to attach. This initiates viral particle internalization through different pathways. HA/Hemagglutinin Protein, H5N1 (Q9Q0U6, sf9, His) is the recombinant Virus-derived HA/Hemagglutinin protein, expressed by Sf9 insect cells , with C-His labeled tag.