D The SARS-CoV-2 RBD from A is shown as a ribbon, colored according to the indicated color gradient, with its N-terminus in blue and C-terminus in red. Disulfide bridges are depicted as yellow sticks. Re9F06 has been omitted for clarity. RBD side chains that interact with the fold-promoting VHH Re9F06 are shown as green "ball-and-sticks". See Appendix Fig S5 for a comprehensive analysis of the Re9F06⋅RBD interface. 