Recombinant SARS-CoV-2, RBD Protein

Severe acute respiratory syndrome coronavirus 2 (SARSCoV2), the causative agent of coronavirus disease 2019 (COVID19), is an enveloped, singlestranded, positivesense RNA virus that belongs to the Coronaviridae family ¹. The SARSCoV2 genome, which shares 79.6% identity with SARSCoV, encodes four essential structural proteins: the spike (S), envelope (E), membrane (M), and nucleocapsid protein (N) ². The S protein is a transmembrane, homotrimeric, class I fusion glycoprotein that mediates viral attachment, fusion, and entry into host cells ³. Each ~180 kDa monomer contains two functional subunits, S1 (~700 a.a) and S2 (~600 a.a), that mediate viral attachment and membrane fusion, respectively. S1 contains two major domains, the Nterminal (NTD) and Cterminal domains (CTD). The CTD contains the receptorbinding domain (RBD), which binds to the angiotensinconverting enzyme 2 (ACE2) receptor on host cells ³⁵. Although both SARSCoV and SARSCoV2 bind the ACE2 receptor, the RBDs only share ~73% amino acid identity, and the SARSCoV2 RBD binds with a higher affinity compared to SARSCoV ^{3, 6}. The RBD is dynamic and undergoes hingelike conformational changes, referred to as the “down” or “up” conformations, which hide or expose the receptorbinding motifs, respectively ⁷. Following receptor binding, S1 destabilizes, and TMPRSS2 cleaves S2, which undergoes a pre to postfusion conformation transition, allowing for membrane fusion ^{8, 9}.

Polyclonal RBDspecific antibodies can block ACE2 binding ^{10, 11}, and antiRBD neutralizing antibodies are present in the sera of convalescent COVID19 patients ¹², identifying the RBD as an attractive candidate for vaccines and therapeutics. In addition, the RBD is poorly conserved, making it a promising antigen for diagnostic tests ^{13 14}. Serologic tests for the RBD are highly sensitive and specific for detecting SARSCoV2 antibodies in COVID19 patients ^{13 15}. Furthermore, the levels of antiRBD antibodies correlated with SARSCoV2 neutralizing antibodies, suggesting the RBD could be used to predict an individual's risk of disease ¹³.

RVQPTESIVRFPNITNLCPFGEVFNATRFASVYAWNRKRISNCVADYSVLYNSASFSTFK CYGVSPTKLNDLCFTNVYADSFVIRGDEVRQIAPGQTGKIADYNYKLPDDFTGCVIAWN SNNLDSKVGGNYNYLYRLFRKSNLKPFERDISTEIYQAGSTPCNGVEGFNCYFPLQSYGF QPTNGVGYQPYRVVVLSFELLHAPATVCGPKKSTNLVKNKCVNFNFNGLTGTGVLTESN KKFLPFQQFGRDIADTTDAVRDPQTLEILDITPCS

Sterile Liquid

The predicted molecular mass is ~33 kDa.

~33 kDa

This recombinant protein is aseptically packaged and formulated in 0.01 M phosphate buffered saline (PBS) pH 7.2 7.4, 150 mM NaCl with no carrier protein, potassium, calcium or preservatives added. Due to inherent biochemical properties of proteins, certain products may be prone to precipitation over time. Precipitation may be removed by aseptic centrifugation and/or filtration.

This recombinant protein may be stored as received at 28°C for up to one month. For longer term storage, aseptically aliquot in working volumes without diluting and store at 80°C. Avoid Repeated Freeze Thaw Cycles.

Next Day Ice Pack

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15. Olba NM, Muller MA, Li W, et al. medRxiv; 2020.