F Crystal structure of free Re5D06, solved to 1.25 Å resolution (Appendix Table S1). Top: free Re5D06 is shown in magenta, with CDR3 (featuring three solvent-exposed tyrosine residues) colored in orange. For comparison, Re5D06 in its RBD-bound conformation is overlayed (RMSD=0.986 Å) in gray. Bottom: intramolecular interactions that stabilize CDR3. CDR3 side chains are depicted in orange; all other side chains are displayed in magenta. See E for further details. Extensive interactions in free Re5D06 stabilize a CDR3 conformation (with solvent-exposed Tyr 104, 109, 112) that requires only relatively minor structural changes for strong RBD binding. 