Contacts between S2 and S1 at capped region and at the S1-S2 cleavage region. The cap region comprises S1 res. 303–549 (mostly RBD region) and S2 res. 735–768/856–985. The S1-S2 cleavage region consists of S1 res. 640–685 and S2 res. 686–700. (a) Contact map between S1 RBD and S2 subunit. (b) Contact map between S1 C-terminal region and S2. (c) Number of residues of S2 (chains A, B, and C) that interact with S1 RBD (chains A, B, and C) at a different position of S2 displacement with and without Nrp1 bound. (d) Number of residues of S2 (chains A, B, and C) that interact with S1 C-terminal region (res. 640–685 only of chain C), again with and without Nrp1 bound. Note that the number of contacts is counted to all three S protein units and temporarily increases as the S1-S2 cleavage region becomes distorted. To see this figure in color, go online.