Recombinant expression of SARS-CoV-2 receptor binding domain (RBD) in Escherichia coli and its immunogenicity in mice

Escherichia coli Nissle 1917 efficiently expresses the RBD domain of SARS-CoV-2 spike protein without codon optimization

Bacterial outer membrane vesicles (OMVs) represent a promising and versatile platform for vaccine delivery. Their inherent self-adjuvant properties and the ability to be adorned with a wide range of heterogeneous antigens position them as a powerful tool in the fight against infectious diseases. Escherichia coli Nissle 1917 (EcN) stands out as a highly valuable probiotic strain because of its long history of safe use and proven clinical benefits in humans. The EcN strain was genetically engineered to derive OMVs displaying receptor binding domain (RBD) of SARS-CoV-2 spike protein on their surface. Although some research groups have previously expressed the SARS-CoV-2 viral spike protein or the RBD in E. coli, particularly in EcN, this study shows a maiden effort to utilize the gene encoding native RBD. The probiotic EcN exhibited a significant level of native RBD expression, demonstrating a more efficient codon usage pattern compared to commonly used bacterial expression systems such as BL21, and DH5α. EcN was engineered to display the native form of viral RBD on the surface using the Lpp-OmpA system. Cell fractionation studies clearly indicated the presence of RBD in the membrane fraction. OMVs displaying RBD on their surface were isolated using ultracentrifugation and the presence of RBD in the OMVs was confirmed by western blot followed by immunofluorescence analyses. Due to their preferential uptake by antigen presenting cells, OMVs derived from EcN bearing native form of RBD hold promise as a potential COVID-19 vaccine candidate.

Isolation and Preliminary Characterization of a Novel scFv against SARS-CoV-2 : an Experimental and Computational Analysis

Background

Since the initial outbreak, the SARS-CoV-2 virus has continued to circulate and mutate, resulting in the emergence of new viral sublineages. Due to the lack of effective protection and therapeutic measures against these new variants, the virus is able to further evolve and diversify. This study aimed to screen a phage antibody library to identify monoclonal antibodies in single-chain variable fragment (scFv) format that target the Receptor Binding Domain (RBD) of different SARS-CoV-2 strains. The newly discovered scFv has the potential for use as a diagnostic or therapeutic option against SARS-CoV-2.

Methods

The RBD protein was produced, purified, and used as an antigen during biopanning. Six rounds of panning enriched RBD-specific phages and the binding affinity of binders were monitored by polyclonal phage ELISA. Subsequently, monoclonal phage ELISA was employed to identify specific binders. After sequence confirmation, the reactivity of the isolated anti-RBD scFv was evaluated. Additionally, bioinformatics tools determined the interaction between selected scFv and SARS-CoV-2 strains.

Results

The ELISA analysis demonstrated that the expressed RBD retains its structural integrity and effectively interacts with antibodies present in the sera of COVID-19 patients. Through screening a phage display library, a strong-binding scFv for RBD was discovered, which can effectively neutralize SARS-CoV-2 and its novel variants.

Conclusion

The findings of this study have led to the discovery of a novel scFv that effectively neutralizes SARS-CoV-2 strains, offering immense potential for research and therapy purposes.

Expression, purification and immunogenicity analyses of receptor binding domain protein of severe acute respiratory syndrome coronavirus 2 from delta variant

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the COVID-19 pandemic. The receptor binding domain (RBD), located at the spike protein of SARS-CoV-2, contains most of the neutralizing epitopes during viral infection and is an ideal antigen for vaccine development. In this study, bioinformatic analysis of the amino acid sequence data of SARS-CoV-2 RBD protein for the better understanding of molecular characteristics was performed. The SARS-CoV-2 RBD gene was inserted into pET-28a vector, and efficiently expressed in E. coli system. Then, the recombinant proteins (RBD monomer and RBD dimer protein) were purified as antigen for animal immunization. Furthermore, the results showed that the recombinant proteins (RBD monomer and RBD dimer protein) had adequate immunogenicity to stimulate specific antibodies against the corresponding protein in immunized mice. Taken together, the results of this study revealed that RBD protein had a high immuno-genicity. This study might have implications for future development of SARS-CoV-2 detection.

Recombinant receptor-binding motif of spike COVID-19 vaccine candidate induces SARS-CoV-2 neutralizing antibody response

Introduction

The SARS-CoV-2 pandemic necessitates effective therapeutic solutions. The receptor-binding motif (RBM) is a subdomain of the spike protein's receptor-binding domain (RBD) and is critical for facilitating the binding of SARS-CoV-2 to the human ACE2 receptor. This study investigates the use of the receptor-binding motif (RBM) domain as an immunogen to produce potent neutralizing antibodies against SARS-CoV-2.

Methods

The RBM gene was codon-optimized and cloned into the pET17b vector for expression in E. coli BL21 (DE3) cells, induced with 1 mM IPTG. The recombinant RBM protein was purified using Ni-NTA affinity chromatography. After validating the recombinant RBM by Western blotting with anti-His tag antibodies, BALB/c mice were immunized with 20 µg of the purified RBM protein. Anti-RBM IgG was subsequently purified using protein G resin, and its neutralizing capacity was assessed using the Pishtaz Teb Zaman Neutralization Assay Kit.

Results

The recombinant RBM protein, with a molecular weight of 10 kDa, was expressed as inclusion bodies. the typical yield of purification was 27 mg/L of bacterial culture. The neutralization test demonstrated a concentration of 36 µg/mL of neutralizing antibodies in the immunized serum, preventing the spike protein from binding to ACE2.

Conclusion

Our study demonstrated that anti-RBM antibodies exhibited neutralization effects on SARS-CoV-2. These findings provide evidence for the development of a vaccine candidate through the induction of antibodies against the RBM, necessitating further studies with adjuvants suitable for human use to evaluate its potential for human vaccination.

Designing and Expression of Recombinant Chimeric Spike Protein from SARS-CoV-2 in Escherichia coli and Its Immunogenicity Assessment

Since December 2019, the world has been grappling with an ongoing global COVID-19 pandemic. Various virus variants have emerged over the past two years, each posing a greater threat than its predecessors. The recent appearance of the omicron variant (B.1.1.529) has raised significant alarm within the field of epidemiology due to its highly contagious nature and rapid transmission rate. The omicron variant possessed mutations in the key receptor-binding domain (RBD) region, the S region, and these modifications have shown a notable impact on the strain's susceptibility to neutralizing antibodies. Developing safe and efficient vaccines to prevent a future severe acute respiratory outbreak of coronavirus syndrome 2 (SARS-CoV-2) is significant. Viral surface spike proteins are ideal targets for vaccines. This study aimed to find a multi-subunit chimeric vaccine. After conducting bioinformatics analysis, the recombinant spike (RS) protein of SARS-CoV-2 was deliberately designed and subsequently produced using E. coli expression systems. The immunogenicity of RS and neutralizing antibody responses were evaluated on immunized BALB/c mice. There was a significant difference in antibody titers between RS-immunized mice and control groups. The endpoint of the serum antibody titer of mice immunized with our chimeric protein was 2.5 times higher than that of the negative control. The chimeric construct could present multiple antigens simultaneously, influentially affecting immunization. Sera from mice vaccinated by RS could recognize the SARS-CoV-2 virus and neutralize antibodies. Our chimeric peptide could bind to antibodies in the serum of patients infected with different serotypes of the SARS-CoV-2 virus, such as alpha, delta, and omicron variants. The results indicated that the RS protein would be a potential novel antigenic candidate for subunit vaccine development and could be used as a useful alternative to generate diagnostic serological tests for SARS-CoV-2 infection.

In silico analysis of the substitution mutations and evolutionary trends of the SARS-CoV-2 structural proteins in Asia

OBJECTIVES

To address a highly mutable pathogen, mutations must be evaluated. SARS-CoV-2 involves changing infectivity, mortality, and treatment and vaccination susceptibility resulting from mutations.

MATERIALS AND METHODS

We investigated the Asian and worldwide samples of amino-acid sequences (AASs) for envelope (E), membrane (M), nucleocapsid (N), and spike (S) proteins from the announcement of the new coronavirus 2019 (COVID-19) up to January 2022. Sequence alignment to the Wuhan-2019 virus permits tracking mutations in Asian and global samples. Furthermore, we explored the evolutionary tendencies of structural protein mutations and compared the results between Asia and the globe.

RESULTS

The mutation analyses indicated that 5.81%, 70.63%, 26.59%, and 3.36% of Asian S, E, M, and N samples did not display any mutation. Additionally, the most relative mutations among the S, E, M, and N AASs occurred in the regions of 508 to 635 AA, 7 to 14 AA, 66 to 88 AA, and 164 to 205 AA in both Asian and total samples. D614G, T9I, I82T, and R203M were inferred as the most frequent mutations in S, E, M, and N AASs. Timeline research showed that substitution mutation in the location of 614 among Asian and total S AASs was detected from January 2020.

CONCLUSION

N protein was the most non-conserved protein, and the most prevalent mutations in S, E, M, and N AASs were D614G, T9I, I82T, and R203M. Screening structural protein mutations is a robust approach for developing drugs, vaccines, and more specific diagnostic tools.