Characterization of SARS-CoV-2 RBD. a Multiple sequence alignment of RBDs of SARS-CoV-2, SARS-CoV, and MERS-CoV spike (S) proteins. GenBank accession numbers are QHR63250.1 (SARS-CoV-2 S), AY278488.2 (SARS-CoV S), and AFS88936.1 (MERS-CoV S). Variable amino acid residues between SARS-CoV-2 and SARS-CoV are highlighted in cyan, and conserved residues among SARS-CoV-2, SARS-CoV, and MERS-CoV are highlighted in yellow. Asterisks represent fully conserved residues, colons represent highly conserved residues, and periods represent lowly conserved residues. The alignment was performed using Clustal Omega. SDS-PAGE (b) and Western blot (c, d) analysis of SARS-CoV-2 RBD. The protein molecular weight marker (kDa) is indicated on the left. SARS-CoV and MERS-CoV RBDs were included as controls. Antisera (1:3,000 dilution) from mice immunized with SARS-CoV RBD (c) and MERS-CoV RBD (d) were used for Western blot analysis