4GMS:
reference: Heterosubtypic antibody recognition of the influenza virus hemagglutinin receptor binding site enhanced by avidity., Lee PS, Yoshida R, Ekiert DC, Sakai N, Suzuki Y, Takada A, Wilson IA, Proc Natl Acad Sci U S A. 2012 Oct 1. PMID: 23027945

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