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. Author manuscript; available in PMC: 2011 Apr 12.
Published in final edited form as: Vaccine. 2008 Sep 12;26(Suppl 4):D49–D53. doi: 10.1016/j.vaccine.2008.07.039

FIGURE 1. Ribbon diagram of an uncleaved hemagglutinin monomer from the 1918 influenza A virus (H1N1), the causative agent of the “Spanish flu” pandemic.

FIGURE 1

The head contains the sialic acid receptor-binding site, which is surrounded by the five predicted antigenic sites (Sa, Sb, Ca1, Ca2, and Cb). The stem comprises helices A and B and the fusion peptide, as shown. (Adapted from a figure, kindly provided by James Stevens and Ian Wilson, in [1].)