5WRG:
reference: Cryo-electron microscopy structures of the SARS-CoV spike glycoprotein reveal a prerequisite conformational state for receptor binding., Gui M, Song W, Zhou H, Xu J, Chen S, Xiang Y, Wang X, Cell Res. 2017 Jan;27(1):119-129. doi: 10.1038/cr.2016.152. Epub 2016 Dec 23. PMID: 28008928

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