SARS-CoV-2 recombinant Spike (SCoV2-rS) glycoprotein trimeric ectodomain from mammalian CHO cells, in glycerol stock
Description: SARS-CoV-2 recombinant Spike (SCoV2-rS) glycoprotein ectodomain expressed as secreted trimeric protein in mammalian (hamster) CHO cells. UniProtKB sequence accession number: P0DTC2 (SPIKE_SARS2); expressed ectodomain includes amino acids (aa) 1-1208. Whole expression construct includes: full-length SCoV2-S ectodomain (aa 1 – 1208) w/o transmembrane and cytoplasmic aa, furin cleavage site “RRAR” mutated to “GSAS”, C-terminal GCN4 trimerization motif fused to protein sequence, then follows thrombin cleavage site, Strep-tag II and His6-tag. Two mutations (K986P and V987P) were introduced into SCoV2-S sequence to stabilize the trimer in the pre-fusion conformation. SCoV2-rS glycoprotein was purified from culture medium under native (non-denaturing) conditions using convenient chromatographic techniques. Final product is formulated in glycerol stock for long-term storage in liquid form at -20°C.
Form: formulated in glycerol stock solution (50%) in PBS (pH 7.4).
Storage: Shipped on dry ice (shipment costs: 130 € to Europe or 150 € to US). Store at -20ºC in liquid form (solution does not freeze at this temperature).
Concentration: 0.5 mg/ml.
Purity: >90 % as determined by SDS-PAGE.
Image: SDS-PAGE showing SCoV2-rS product 20-S2S-TCg-G at approximately 160 kDa (3 μg/lane).
Applications (tested): ELISA, other immunoassays, Electron microscopy, Western blot, SDS-PAGE.
Quality: According to the expressed construct, purified SCoV2-rS protein should be trimer in the stabilized prefusion conformation. Full-length trimeric protein enables detection of more antibodies against SCoV2-S, than shorter protein constructs (e.g., RBD or S1). This product has been compared both with S1 recombinant protein in ELISA and S1 antigen-based CE-approved commercial IVD tests using the same set of human sera. Results for sensitivity and specificity are provided in the Table below:
| Reference test for Covid-19 positive sera |
RT-PCR |
|||
| Analyzed antigens or serological tests | SARS2 S IgG (Baltymas) | SARS2 S1 IgG (Sino Biological) |
AMP rapid IgG test | Euroimmun ELISA (S1) IgG test |
| Sensitivity (n=50), correct positives | 94.00% | 78.00% | 92.00% | 92.00% |
| Specificity (n=150 or n=160), correct negatives | 99.38% (n=160) |
97.33% (n=150) |
99.38% (n=160) |
98.75% (n=160) |
| OD mean for positive sera (n=50) | >2,718* | 0,980 | N. A. | 1,820 |
| Accuracy** | 99.11% | N. A. | 99.01% | 98.41% |
*The exact OD mean for Baltymas S protein is higher, as in three cases OD reached maximal value (4,000) of the equipment used.
** assuming a COVID prevalence of 5%, this indicates the likelihood that the test will correctly classify samples as positive and negative.
Comparison of Baltymas’s product 20-S2S-TCg-G (green) with EUROIMMUN AG (Germany) Anti-SARS-CoV-2 ELISA IgG (red) used as a “gold standard” (product No. EI 2606-9601 G; CE-marked and FDA-approved by EUA) in semi-quantitative IgG ELISA by testing 50 COVID-19 PCR-positive patient sera is shown below:
Reactivity of SCoV2-rS glycoprotein (current batch of product 20-S2S-TCg-G) with specific IgG in ELISA using pools of Covid-19 positive and negative sera:
Applications (approved): This SCoV2-rS product has been used in two CE-marked IVD tests, semi-quantitative and quantitative (in BAU/ml) IgG ELISAs.
Unit/Price:
| Size | Catalogue No. | Price | |
| 50 μg | 20-S2S-TCg-G-L | 250 € | Inquiry / Order product |
| 100 μg | 20-S2S-TCg-G-C | 400 € | |
| 500 μg | 20-S2S-TCg-G-D | 1500 € | |
| 1 mg | 20-S2S-TCg-G-M | 2500 € |