Published:
6/25/2020

Scientists at the Frederick National Laboratory for Cancer Research (FNL) successfully increased the yield production of a challenging protein used in antibody tests for SARS-CoV-2, the virus behind COVID-19, publishing their findings earlier this month in Protein Expression and Purification. 

3D print of a spike protein on the surface of SARS-CoV-2—also known as 2019-nCoV, the virus that causes COVID-19. Spike proteins cover the surface of SARS-CoV-2 and enable the virus to enter and infect human cells.
3D print of a spike protein on the surface of SARS-CoV-2—also known as 2019-nCoV, the virus that causes COVID-19. Spike proteins cover the surface of SARS-CoV-2 and enable the virus to enter and infect human cells. Source: NIH

With large-scale SARS-CoV-2 serological surveys underway in the United States, laboratories need a reliable source of key proteins in sufficient quantity to determine how many adults with no confirmed history of COVID-19 actually possess antibodies to the novel coronavirus. The SARS-CoV-2 spike protein is vital for these efforts; however producing sufficient quantities to test thousands of blood samples was a challenge due to the protein’s inherent instability. 

“Most antibodies people generate against this virus are for the spike protein,” said Dominic Esposito, Ph.D., who leads the Protein Expression Laboratory at FNL. “For this reason, it’s a vital reagent for assay development, but there are significant and unexplained issues with low yield for the spike protein when we try to produce it recombinantly.” 

High demand calls for higher protein yield 

The laboratory delved into this process improvement as part of a collaboration with investigators across the National Institutes of Health (NIH) seeking to create a SARS-CoV-2 antibody test with maximum sensitivity. This test was developed for the NIH’s serosurvey with more than 10,000 participants, aiming to determine the extent to which COVID-19 has spread undetected in the United States. 

Esposito said the FNL and NIH collaborators improved the spike protein production process, paving the way for other laboratories to successfully produce high-quality proteins and meet the growing need for SARS-CoV-2 serology tests. 

Adjustments to temperature and harvest time optimized production 


Fig. 2 from the published abstract: Representative IMAC chromatography fraction analyses and purified proteins.

According to the study, the standard yield for the protein was 1 to 2 mg/liter. By decreasing the temperature by 5 degrees Celsius and increasing the harvest time by one day, Esposito and his team managed to get a yield of 5 mg/liter or greater. Ultimately, Esposito said none of the adjustments they made were “earth shattering” on their own, but added up to an enhanced process with increased yield and purity. Every increment counts, he added, when trying to produce proteins for thousands of antibody tests. 

“None of these tests work without good quality proteins,” Esposito said. 

In order to accurately test the presence of an antibody, Esposito said serology tests rely on  viral proteins produced in the laboratory. The study focused on two spike protein expression constructs, VRC and Mt. Sinai. The VRC spike construct was generated by Jason McLellan, Ph.D. at the University of Texas at Austin and was provided by the National Institute for Allergy and Infectious Diseases, while the Mt. Sinai construct was provided by the Icahn School of Medicine. According to the study, the VRC spike construct consistently generated higher purity protein at higher yield. 

Merging old and new technologies led to success 

For this study, the team used magnetic bead technology for the first time at FNL to evaluate how the shorter process compared to traditional methods. The beads capture the protein in a batch, which proved to be five times faster with comparable purity, Esposito said. These results show possibility for future study, he added. 

Esposito said the laboratory has been able to transition to this work due to the resources and infrastructure it uses as part of the National Cancer Institute’s RAS Initiative run by FNL. Esposito added a lot of the laboratory’s ability for large scale mammalian protein production stems from prior work during the Ebola outbreak. 

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