Recombinant SARS-CoV-2 Spike RBD-His-Avi, 100ug

Recombinant SARS-CoV-2 Spike RBD-His-Avi

Source: Recombinant SARS-CoV-2 Spike RBD (Arg319-Asn532) was expressed in mammalian cells with a His tag and Avi at the C-terminus.
Accession: QHD43416.1
Predicted molecular mass: 27 kDa. Due to glycosylation, the recombinant SARS-CoV-2 Spike RBD migrates to 36-40 kDa based on the Bis-Tris PAGE result.
Endotoxin: Less than 1 EU per ug by the LAL method.
Formulation: The recombinant SARS-CoV-2 Spike RBD-His-Avi was lyophilized from 0.22 um filtered solution in 20 mM PB (pH 7.4). Normally 5% trehalose is added as protectant before lyophilization.
Purity: > 95% by PAGE under reduced condition, and SEC-HPLC.

Shipping: The product is shipped with ice packs. Upon receipt, store it immediately at the temperature recommended below.
Stability & Storage:
Use a manual defrost freezer and avoid repeated freeze-thaw cycles.
12 months from date of receipt, -20 to -70°C as supplied.
1 month, 2 to 8°C under sterile conditions after reconstitution.
3 months, -20 to -70°C under sterile conditions after reconstitution.

Background

The receptor binding domain (RBD) in the S1 subunit of the SARS-CoV-2 (2019-nCoV) spike (S) glycoprotein plays the most important roles in viral attachment, fusion and entry, and serves as a target for development of virus entry inhibitors, neutralizing antibodies, and vaccines. There are two subunits, S1 and S2, in the SARS-CoV-2 spike (S) glycoprotein. The S1 subunit, the N-terminal 14–685 amino acids of S protein, contains N-terminal domain (NTD), receptor binding domain (RBD, 331-524), and receptor binding motif (RBM). The SARS-CoV and SARS-CoV-2 S proteins mediate viral entry into host cells by binding to a host receptor, angiotensin-converting enzyme 2 (ACE2), through the receptor-binding domain (RBD), and then fusing the viral and host membranes through the S2 subunit. The ACE2-binding affinity of the Spike RBD of SARS-CoV-2 is 10- to 20-fold higher than that of SARS-CoV.

The RBD in the SARS-CoV-2 S protein has become a popular target of antibodies for diagnostics test and proteins and antibodies for therapeutic drugs. It is critical to use an active protein with natural conformation and post-translational modification as the antigen, even for the IgM/IgG test kit which is popularly used to check people already carrying immune response against the COVID-19 virus. Thus, the spike RBD protein should be expressed in mammalian cells, such as HEK 293 and CHO cells.

The amino-acid sequence identity is around 74% between the RBDs in the SARS-CoV and SARS-CoV-2 spike proteins, similar to the 77% identity between the whole spike proteins of SARS-CoV and SARS-CoV-2. Such a high degree of sequence similarity raises the possibility that cross-reactive epitopes may exist. Although the SARS-CoV RBD polyclonal antibodies can recognize both viruses, only one out of a few published RBD monoclonal antibodies neutralizing SARS-CoV binds to SARS-CoV-2 spike RBD. Out of the 28 residues in the epitope of the S1 RBD monoclonal antibody, only 4 residues (86%) in SARS-CoV-2 are different from SARS-CoV. However, the S1 RBD mAb binds to SARS-CoV spike RBD (Kd = 1 nM) with a much higher affinity than to SARS-CoV-2 spike RBD (Kd = 115 nM, or 6.3 nM measured by another lab).

Recombinant SARS-CoV-2 S RBD-His and RBD-Fc proteins are both available with an Avi site, which is for biotinylation. Biotinylated recombinant SARS-CoV-2 S RBD-His and RBD-Fc proteins as well as the S1 RBD monoclonal antiobdy are also available. Please ask for a quote if you need RBD mutants or a protein with different modification or components.