Scientists identify novel epitope in SARS-CoV-2 spike furin cleavage site

Scientists have identified an immunogenic epitope in the furin cleavage site of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that elicits strong antibody responses in coronavirus disease 2019 (COVID-19) patients. did.In their study published in the journal eBio Medicine, Researchers also identified a monoclonal antibody that binds to this epitope and protects mice from SARS-CoV-2 infection.

study: Identification of immunogenic epitopes and protective antibodies against the furin cleavage site of SARS-CoV-2Image credit: CI Photos / Shutterstock.com

Background

SARS-CoV-2 contains a unique four amino acid insertion (PRRA) between the S1 and S2 subunits. spike proteinThis unique insertion creates a transmembrane protease serine 2 (TMPRSS2)/furin cleavage site in the spike protein, increasing SARS-CoV-2 infectivity. Sequential cleavage of spike proteins at her S1/S2 and S2′ cleavage sites by furin and her TMPRSS2 is essential for virus entry and infectivity.

In the current study, scientists identify an immunogenic epitope in the furin cleavage site that specifically recognizes immunoglobulin G (IgG) and IgM antibodies in COVID-19 patients.

Identification and characterization of novel spike epitopes

Scientists screened spike epitopes using predictions from immune epitope databases and analytical resources, ultimately identifying seven peptides. Structural models of these proteins were then built using computer-guided homology modeling techniques.

In addition, researchers chemically synthesized these peptides and subjected them to an enzyme-linked immunosorbent assay (ELISA) to identify peptide-specific antibodies in COVID-19 patients and healthy individuals. The strongest antibody response was detected against the peptide at spike positions 672-691, indicating that this peptide contains an immunogenic epitope.

Comparison of peptide sequences with other humans coronavirus revealed that the peptide contains a PRRA between the S1 and S2 subunits that is not present in other coronaviruses.

ELISA results revealed that both IgG and IgM antibodies targeting the spike peptide 672-691 were present in significantly higher concentrations in COVID-19 and suspected patients than in healthy individuals .

Scientists further tested the applicability of the spike peptide as an immunogenic antigen for the diagnosis of COVID-19. These experiments revealed that serum titers of peptide-specific IgG antibodies may serve as potential biomarkers for diagnostic purposes.

Antiviral effect of spike peptide

Scientists developed a synthetic version of spike peptide 672-691 to determine its ability to prevent SARS-CoV-2 infection in cultured cells. To this end, 672-691 was found to block wild-type SARS-CoV-2 and omicron mutants from infecting cells.

We then treated mice with peptides and subsequently collected serum samples to determine their virus-neutralizing efficiency. To this end, serum samples obtained from mice treated with 672-691 were able to prevent SARS-CoV-2 infection.

Researchers also introduced deletion mutations within the spike peptide to isolate specific antibody-binding regions. The identified immunogenic epitopes of 672-691 were found to overlap with PRRAs unique to SARS-CoV-2.

Spike peptide-specific monoclonal antibody response

Peripheral blood mononuclear cells from COVID-19 patients were screened for spike peptide-specific human monoclonal antibodies. Multiple phage clones were obtained, followed by sequence analysis to identify two independent clones.

A monoclonal antibody generated from one of these clones showed strong binding affinity to spike peptides derived from wild-type SARS-CoV-2 and the Omicron variant. However, further analysis using a mutant virus strain revealed that the spike peptide lacking the PRRA insertion did not bind to this monoclonal antibody, thus indicating that the monoclonal antibody binds directly to the furin cleavage site of the spike protein. rice field.

About antivirus Effectivenessa monoclonal antibody significantly reduced viral ribonucleic acid (RNA) titers in the lungs of SARS-CoV-2-infected mice.

Significance of research

The current study identifies an immunogenic epitope in the furin cleavage site of the SARS-CoV-2 spike protein. This epitope elicits a strong antibody response in COVID-19 patients. The researchers also identified a human monoclonal antibody that targets this epitope and prevents mice from developing SARS-CoV-2 infection.

Overall, the results of this study highlight that apart from creating a furin cleavage site between the S1 and S2 subunits, the spike protein PRRA generates highly immunogenic epitopes. Antibodies that bind to spike proteins outside the well-established receptor-binding domain (RBD) may therefore also have potent antiviral activity.