SARS-CoV-2 Spike Protein and Bioactive Compound Interactions

Recombinant SARS-CoV-2 spike protein S1 (Figure 2) was obtained from RayBiotech (Peachtree Corners, GA, USA). The 23-mer SBP-1 peptide was purchased from LifeTein (Hillsborough, NJ, USA). The custom peptide TVFGLNVWKRYSK was synthesized by Pierce Custom Peptides (ThermoFisher; Rockford, IL). Licochalcone A, imatinib, mycophenolic acid, quinacrine, and HPLC-grade methanol and acetonitrile were purchased from Sigma Aldrich (St. Louis, MO, USA). LC-MS grade formic acid and rapid equilibrium dialysis single use plates were purchased from ThermoFisher (Waltham, MA, USA). Magnetic microbeads derivatized with Ni²⁺-nitrilotriacetic acid were obtained from EmerTher (Parsippany, NJ, USA). Polypropylene 2-mL conical bottom 96-well plates were purchased from Fisher Scientific (Hanover Park, IL, USA), and ultrapure water was prepared in house using a Milli-Q water purification system (Millipore, MA, USA). Extracts of Dioscorea villosa, Glycyrrhiza glabra, Glycyrrhiza inflata, Humulus lupulus, and Trifolium pratense L. were prepared, botanically authenticated and chemically standardized as previously described.^{11 (link),22 (link)} For example, G. inflata roots were powdered, extracted by percolation with methanol (weight powder/volume of solvent, 1/20), and freeze dried (extraction yield 25% w/w, weight of extract/weight of root powder).^{22 (link)}