Purified RBD was combined separately with Strep-tagged Fab150, Fab58, scFv269 and Fab316 in a 1:1 molar ratio, with final concentrations of 13.2, 9.4, 12.7 and 13.0 mg ml-1, separately. RBD was combined with Fab45 and Strep-tagged Fab88, Fab75 and Fab253, and Fab 75 and Strep-tagged chimeric Fab 253H55L in a 1:1:1 molar ratio all with a final concentration of 7 mg ml−1, separately. Glycosylated RBD was combined with Fab S309 (Pinto et al., 2020) and Fab384 in a 1:1:1 molar ratio with a final concentration of 8 mg ml−1. These complexes were separately incubated at room temperature for 30 min. Initial screening of crystals was set up in Crystalquick 96-well X plates (Greiner Bio-One) with a Cartesian Robot using the nanoliter sitting-drop vapor-diffusion method, with 100 nL of protein plus 100 nL of reservoir in each drop, as previously described (Walter et al., 2003). Good crystals of RBD-150 complex were formed in Molecular Dimensions Morpheus condition C2, containing 0.09 M NPS (nitrate, phosphate and sulfate), 0.1 M MES/imidazole pH 6.5, 10% (w/v) PEG 8000 and 20% (v/v) ethylene glycol and crystals also formed in Hampton Research PEGRx condition D11, containing 0.1 M imidazole pH 7.0 and 12% (w/v) PEG 20000. Some good crystals of RBD-158 were obtained from Index condition C01, containing 3.5 M NaCOOH pH 7.0, while some crystals were formed in Proplex condition C1, containing 0.15 M (NH4)2SO4, 0.1 M Tris pH 8.0 and 15% (w/v) PEG 4000 and further optimized in 0.15 M (NH4)2SO4, 0.1 M Tris pH 7.6 and 14.6% (w/v) PEG 4000. Crystals of RBD-scFv269 complexed were obtained from Index condition F01, containing 0.2 M Proline, 0.1 M HEPES pH 7.5 and 10% (w/v) PEG 3350. Good crystals for the RBD-316 complex were obtained from Index condition G10, containing 0.2 M MgCl2, 0.1 M bis-Tris pH 5.5 and 25% (w/v) PEG 3350. Crystals of RBD-45-88 complex were obtained from PEGRx condition G12, containing 10% (v/v) 2-Propanol, 0.1 M Sodium acetate trihydrate pH 4.0, 22% (w/v) PEG 6000. Crystals of RBD-75-253 complex were obtained from PEGRx condition D8, containing 0.1 M BIS-TRIS pH 6.5, 16% (w/v) PEG 10000. Crystals of RBD-75-253H55L were obtained from Index condition F5, containing 0.1 M ammonium acetate, 0.1 M bis-Tris pH 5.5 and 17% (w/v) PEG 10000. For the RBD-S309-384 ternary complex, good crystals were obtained from Morpheus condition H1, containing 0.1 M amino acids (Glu, Ala, Gly, Lys, Ser), 0.1 M MES/imidazole/ pH 6.5, 10% (w/v) PEG 20000 and 20% (w/v) PEG MME 550.

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