A Cryptic Site of Vulnerability on the Receptor Binding Domain of the SARS-CoV-2 Spike Glycoprotein

M. Gordon Joyce; Rajeshwer S. Sankhala; Wei-Hung Chen; Misook Choe; Hongjun Bai; Agnes Hajduczki; Lianying Yan; Spencer L. Sterling; Caroline E. Peterson; Ethan C. Green; Clayton Smith; Natalia de Val; Mihret Amare; Paul Scott; Eric D. Laing; Christopher C. Broder; Morgane Rolland; Nelson L. Michael; Kayvon Modjarrad

Center for Disease Control, and the University of Sydney, Sydney, Australia released the sequence of a coronavirus genome from a case of a respiratory disease from Wuhan on January 10 th available at recombinomics.co/topic/4351-wuhan-coronavirus-2019-ncov-sequences/. The sequence was also deposited in GenBank (accession MN908947) and GISAID (>EPI_ISL_402125). DNA encoding the SARS-Cov-2 RBD (residues 331-527) was synthesized (Genscript) with a C-terminal His6 purification tag and cloned into a CMVR plasmid, and protein was expressed by transient transfection in 293F cells for six days. The SARS-CoV-2 RBD-His protein was purified from cell culture supernatant using a Ni-NTA (Qiagen) affinity column. DNA encoding the S protein ectodomains (residues 1-1194) from bat SARSrelated CoV isolates Rs4231 and Rs4874 (ref. (Hu et al., 2017) ) were synthesized (Genscript) with a Cterminal T4-Foldon domain or C-terminal GCN domain, respectively, followed by factor xA cleavage sites and Strep-Tactin purification tags. Bat SARSr-CoV S genes were cloned into a modified pcDNA3.1 expression plasmid (Chan et al., 2009) . Protein was initially expressed by transient transfection in 293F cells for six days, then serial cloned to select stably expressing cell lines (Yan L., in submission) . The Rs4231-T4 and Rs4874-GCN S proteins were purified from cell culture supernatant using a Strep-Tactin affinity column. The oligomeric structure of these S proteins was selected by size exclusion chromatography (GE/AKTA) and trimeric S proteins were confirmed by Native-PAGE. SARS S-2P was produced as previously described, with Strep-Tactin affinity chromatography followed by gel filtration using a 16/60 Superdex-200 purification column. Purification purity for all S glycoproteins was assessed by SDS-PAGE.