Product Description

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.

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Unit/Price:

Size Catalogue No. Price
50 μg 20-S2S-TCg-G-L 250 €
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100 μg 20-S2S-TCg-G-C 400 €
500 μg 20-S2S-TCg-G-D 1500 €
1 mg 20-S2S-TCg-G-M 2500 €