Figure 3 . Comparison of different apo spike glycoprotein variants. Structural comparison of the apo- mink S glycoprotein determined in this study [PDB: 8T21] (A) with previously reported apo- mink S glycoprotein [PDB ID: 7LWI] (B), Alpha S [PDB:7R13] (C), Delta S [PDB: 7SBK] (D), and Omicron S [PDB: 7T9J] (E). The sequence alignment of the S glycoproteins RBD is shown below, and the conserved residues are indicated in black. Notable mutations in the mink S glycoprotein include substitution mutation Y453F.