Natural Antibodies Produced in Vaccinated Patients and COVID-19 Convalescents Recognize and Hydrolyze Oligopeptides Corresponding to the S-Protein of SARS-CoV-2

Abstract

The S-protein is the major antigen of the SARS-CoV-2 virus, against which protective antibodies are generated. The S-protein gene was used in adenoviral vectors and mRNA vaccines against COVID-19. While the primary function of antibodies is to bind to antigens, catalytic antibodies can hydrolyze various substrates, including nucleic acids, proteins, oligopeptides, polysaccharides, and some other molecules. In this study, antibody fractions with affinity for RBD and S-protein (RBD-IgG and S-IgG) were isolated from the blood of COVID-19 patients vaccinated with Sputnik V. The fractions were analyzed for their potential to hydrolyze 18-mer oligopeptides corresponding to linear fragments of the SARS-CoV-2 S-protein. Here, we show that the IgG antibodies hydrolyze six out of nine oligopeptides efficiently, with the antibodies of COVID-19-exposed donors demonstrating the most significant activity. The IgGs of control donors not exposed to SARS-CoV-2 were found to be inactive in oligopeptide hydrolysis. The antibodies of convalescents and vaccinated patients were found to hydrolyze oligopeptides in a wide pH range, with the optimal pH range between 6.5 and 7.5. The hydrolysis of most oligopeptides by RBD-IgG antibodies is inhibited by thiol protease inhibitors, whereas S-IgG active centers generally combine several types of proteolytic activities. Ca2+ ions increase the catalytic activity of IgG preparations containing metalloprotease-like active centers. Thus, the proteolytic activity of natural antibodies against the SARS-CoV-2 protein is believed to be due to the similarity of catalytic antibodies’ active centers to canonical proteases. This work raises the question of the possible physiological role of proteolytic natural RBD-IgG and S-IgG resulting from vaccination and exposure to COVID-19.

Identification of Antibody-Mediated Hydrolysis Sites of Oligopeptides Corresponding to the SARS-CoV-2 S-Protein by MALDI-TOF Mass Spectrometry

“…The groups of 25 donors each involved in this study were described in our previous work [ 14 ]. These are COVID-19 survivors who were then vaccinated with Sputnik V (Con + Vac group), COVID-19 survivors (Con group), and healthy peoples vaccinated with Sputnik V (Vac group).…”

“…It has been shown that S-IgG antibodies hydrolyze oligopeptides corresponding to the epitopes of the S-protein. Antibodies without affinity for the S-protein were not active in the hydrolysis of any oligopeptides that were used in this research [ 14 ].…”

“…Thus, the accumulation of reaction products and characterization of the oligopeptide hydrolysis reaction by antibodies was carried out. Only six of the nine oligopeptides under study were shown to be hydrolyzed by antibodies from COVID-19 exposed and/or vaccinated patients [ 14 ]. It should be noted that IgG, which does possess an affinity for SARS-CoV-2 proteins, was not active in the hydrolysis of all the oligopeptides.…”

Natural Antibodies Produced in Vaccinated Patients and COVID-19 Convalescents Hydrolyze Recombinant RBD and Nucleocapsid (N) Proteins

“…For example, it has been shown that the IgG of SLE patients is most active in the presence of Ca 2+ , Mg 2+ , Co 2+ , and Ni 2+ ions [16]. The increase in the activity of RBD-IgG and S-IgG during the hydrolysis of S-protein oligopeptides has been reported to occur in the presence of Ca 2+ ions [27].…”