SARS-CoV-2 RBD Fab Complex Crystallization

FD-5D and FI-3A Fabs were mixed with RBD separately with a final concentration of 13 mg/mL. FI-3A and FD-11A Fabs were mixed with RBD in a 1:1:1 molar ratio with a final concentration of 7 mg/mL. After incubation at room temperature for 30 min, the samples were used for initial screening of crystals 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 and 100 nL of reservoir in each drop, as previously described 18 (link). Crystals of RBD/FD-5D Fab complex were obtained from Molecular Dimensions Morpheus screen, condition C9 containing 10% (w/v) PEG 20 000, 20% (v/v) PEG MME 550, 0.03 M of each NPS (NaNO₃; Na₂HPO₄; (NH₄)₂SO₄) and 0.1 M bicine/Trizma base pH 8.5. Tiny Crystals of RBD/FI-3A Fab complex were first formed in Hampton Research PEGRx screen, condition A10, containing 0.1 M sodium citrate tribasic and 30% (w/v) PEG 550 and further optimized in 0.08 M sodium citrate tribasic and 24% (w/v) PEG 550. Crystals of RBD/FI-3A/FD-11A Fabs complex were formed in Hampton Research Index screen, condition 25, containing 3.5 M sodium formate pH 7.0 and further optimized in 2.9 M sodium formate pH 7.0.