Cα network analysis of three antibody–antigen complexes. Circles indicate antigen (spike-protein receptor-binding domain), and cubes represent antibody or angiotensin-converting enzyme 2. Columns list complexes 3D0G, 6M0J, and 6W41. Rows represent FRI, betweenness centrality, eigencentrality, and subgraph centrality. Abbreviations: FRI, flexibility–rigidity index; PDB, Protein Data Bank.