SARS-CoV-2 publication preview

Publication: Trimeric SARS-CoV-2 Spike Proteins Produced from CHO Cells in Bioreactors Are High-Quality Antigens

Published in: Processes 2020, 8(12), 1539;

Authors: Paco Pino, Joeri Kint, Divor Kiseljak, Valentina Agnolon, Giampietro Corradin, Andrey V. Kajava, Paolo Rovero, Ronald Dijkman, Gerco den Hartog, Jason S. McLellan, Patrick O. Byrne, Maria João Wurm and Florian M. Wurm.

Read the full paper on the Processes website

Stabilized trimeric spike protein (Wuhan)

We are proud to have created a stable, clonally derived, recombinant, suspension grown CHO cell line that produces a secreted, stabilized version of the trimeric spike protein of SARS-CoV-2.

This cell line is suitable for large scale manufacturing in chemically defined media. The secreted trimeric spike accumulates in the protein-free cell culture fluid of the cells. Our multi-step, HPLC-based purification process further ensures that the resulting trimeric protein is of high purity (> 95 %).

This protein is now available for applications such as diagnostics, R&D and vaccine development.

Product: Stabilized Trimeric Spike Protein SARS-CoV-2 (Wuhan)
Modifications C-terminal Transmembrane region replaced with a trimerization domain and a polyhistidine tag. Two stabilizing proline mutations and scrambled S1/S2 furin cleavage site
Isolate (Seq ID) Wuhan-Hu-1 (GenBank: MN908947)
Expression System CHOExpressTM cells
Purity > 90 % as determined by SDS-PAGE
Buffer 0.01M PBS, pH 7.4, no preservatives

D614G mutant

Since the beginning of the COVID-19 pandemic in Wuhan, variants of the SARS-CoV-2 virus carrying a mutation in the spike protein at position 614 have largely replaced the original isolate [8].

Protein modelling has shown that this D614G mutation has a significant influence on the conformation of the trimeric spike. These structural changes in the G614 variant seem to enhance infectivity of virions through improved binding to the ACE2 receptor [4, 10, 15].

In addition, there are reports that antibodies generated against the Wuhan variant of SARS-CoV-2 may not fully protect against D614G [2, 6]. Interestingly, all current vaccines and diagnostic tests have been developed on the basis of the Wuhan isolate.

It is unclear, but not unthinkable that current vaccine candidates will be less effective against viruses carrying the D614G mutation. In addition, current antibody tests may display decreased sensitivity to antibodies against the 614G variant.

We offer the trimeric spike protein with the D to G mutation as well as the 614D ‘Wuhan’ trimeric protein. This makes these proteins ideal for use in comparative studies.

Product: Stabilized trimeric spike protein SARS-CoV-2 (D614G mutant)
Modifications C-terminal Transmembrane region replaced with a trimerization domain and a polyhistidine tag. Two stabilizing proline mutations. Scrambled S1/S2 furin cleavage site. D614G mutation
Isolate (Seq ID) Wuhan-Hu-1 (GenBank: MN908947) D614G variant
Expression System CHOExpressTM cells
Purity > 90 % as determined by SDS-PAGE
Buffer 0.01M PBS, pH 7.4, no preservatives

Receptor binding domain (RBD), monomeric

Additionally, we offer the RBD domain produced in the same CHO cell system. The RBD protein is located in the S1 part of the spike protein and is easier to produce and purify because of its' small size. This makes it an ideal alternative for applications where costs are the driving factor. Please contact us to learn about our pricing per gram or mg of RBD protein.

Product: Receptor binding domain (RBD) SARS-CoV-2, monomeric
Modifications C-terminal extended with a strep and a polyhistidine tags.
Isolate (Seq ID) Wuhan-Hu-1 (GenBank: MN908947)
Expression System CHOExpressTM cells
Purity > 90 % as determined by SDS-PAGE
Buffer 0.01M PBS, pH 7.4, no preservatives


It is now well established that antibodies directed against SARS-CoV-2 can protect an individual against COVID-19. Diagnostic tests that detect and quantify these antibodies in blood or saliva are a vital tool for clinicians to answer important questions:

  • Has an individual gone through an infection (possibly a-symptomatic)?
  • Has an individual responded immunologically to exposure with a vaccine candidate?
  • Does an individual have antibody levels that are high enough to protect against (re)infection?

To protect against SARS-CoV-2, a patients’ antibodies need to be directed against critical parts of the virus. In fact, hospitalized patients that have antibodies mainly directed towards the ‘wrong’ part of the virus (the Nucleocapsid protein) were shown to be more likely to die [1]. The most efficient antibodies against the virus are so-called neutralizing antibodies, which seem to be exclusively directed against the Spike protein [9].

Antibody levels in hospitalized COVID-19 patients are generally high and fairly easy to detect. In contrast, these levels are much lower in people that have resolved the infection with little or no clinical symptoms. It is reasonable to expect that similar, low levels of antibodies are to be expected in response to vaccination.

Because low levels of antibodies against the SARS-CoV-2 spike can protect an individual against COVID-19, it is essential that diagnostic tests have sufficient sensitivity to detect low levels of antibodies.

The ideal diagnostic test for SARS-CoV-2 antibodies would be one that is able to detect all antibodies directed against the spike protein. To do this, one would need to produce highly purified spike proteins in its ‘natural’ conformation.

This turned out to be problematic; the monomeric spike protein is large (150 kD), heavily glycosylated and inherently unstable. The protein is readily cleaved by furin-proteases and it can change conformation easily. To make matters worse, the spike is presented on the virus particle as a homo-trimer complex; however, the monomers are not covalently bound to each other.

Current diagnostic tests lack the sensitivity to detect low levels of antibodies

Because of these issues, currently available tests were developed on the basis of fragments of the spike protein to detect antibodies against SARS-CoV-2 [12, 13, 3, 7]. Recently, a version of the spike protein was developed and published [5, 14] that appears more stable, forms trimers and is also glycosylated [11].

This stabilized trimeric protein was used as a template for many of the SARS-CoV-2 vaccine candidates (Novavax, Moderna, Pfizer/BioNTech, GSK/Clover, CureVac and others) either as an encoding RNA molecule, presented on a virus-vector or as subunit protein based vaccine concept.

Useful links to webpages that track the development of COVID-19 vaccines and treatments: Milken Institute Covid-19 Treatment and Vaccine Tracker and NYTimes Coronavirus Vaccine Tracker.

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  4. The Spike D614G Mutation Increases SARS-CoV-2 Infection of Multiple Human Cell Types 2020 Daniloski, Z., Jordan, T., Ilmain, J., Guo, X., Bhabha, G., tenOever, B., & Sanjana, N. CrossRef
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  6. The D614G Mutation of SARS-CoV-2 Spike Protein Enhances Viral Infectivity and Decreases Neutralization Sensitivity to Individual Convalescent Sera 2020 Hu, J., He, C. L., Gao, Q., Zhang, G. J., Cao, X. X., Long, Q. X., Deng, H. J., Huang, L. Y., Chen, J., Wang, K., Tang, N., & Huang, A. L. BioRxiv, 2020.06.20.161323. | CrossRef
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  9. Potent Neutralizing Antibodies Against Multiple Epitopes on SARS-CoV-2 Spike 2020 Liu, L., Wang, P., Nair, M. S., Yu, J., Rapp, M., Wang, Q., Luo, Y., Chan, J. F. W., Sahi, V., Figueroa, A., Guo, X. V., Cerutti, G., Bimela, J., Gorman, J., Zhou, T., Chen, Z., Yuen, K. Y., Kwong, P. D., Sodroski, J. G., … Ho, D. D. Nature, 584(7821), 450–456. | CrossRef
  10. Spike Mutation D614G Alters SARS-CoV-2 Fitness and Neutralization Susceptibility 2020 Plante, J. bioRxiv. Preprint. 2020 Sep 2. (1-38) | CrossRef
  11. Site-Specific Glycan Analysis of the SARS-CoV-2 Spike 2020 Watanabe, Y., Allen, J. D., Wrapp, D., McLellan, J. S., & Crispin, M. Science, 369(6501), 330–333. | CrossRef
  12. Performance Evaluation of Serological Assays to Determine the Immunoglobulin Status in SARS-CoV-2 Infected Patients 2020 Wechselberger, C., Süßner, S., Doppler, S., & Bernhard, D. Journal of Clinical Virology, 131. | CrossRef
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