5VTR:
reference: Diversity of Functionally Permissive Sequences in the Receptor-Binding Site of Influenza Hemagglutinin., Wu NC, Xie J, Zheng T, Nycholat CM, Grande G, Paulson JC, Lerner RA, Wilson IA, Cell Host Microbe. 2017 Jun 14;21(6):742-753.e8. doi: 10.1016/j.chom.2017.05.011. PMID: 28618270

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).