ABSTRACT
COVID-19 is a highly infectious disease caused by a newly emerged coronavirus (SARS-CoV-2) that has rapidly progressed into a pandemic. This unprecedent emergency has stressed the significance of developing effective therapeutics to fight the current and future outbreaks. The receptor-binding domain (RBD) of the SARS-CoV-2 surface Spike protein is the main target for vaccines and represents a helpful "tool" to produce neutralizing antibodies or diagnostic kits. In this work, we provide a detailed characterization of the native RBD produced in three major model systems: Escherichia coli, insect and HEK-293 cells. Circular dichroism, gel filtration chromatography and thermal denaturation experiments indicated that recombinant SARS-CoV-2 RBD proteins are stable and correctly folded. In addition, their functionality and receptor-binding ability were further evaluated through ELISA, flow cytometry assays and bio-layer interferometry.
Subject(s)
COVID-19/metabolism , SARS-CoV-2/metabolism , Spike Glycoprotein, Coronavirus/metabolism , Animals , Cell Line , Escherichia coli/genetics , Gene Expression , HEK293 Cells , Humans , Insecta/cytology , Protein Binding , Protein Denaturation , Protein Domains , Protein Folding , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , SARS-CoV-2/chemistry , SARS-CoV-2/genetics , Spike Glycoprotein, Coronavirus/chemistry , Spike Glycoprotein, Coronavirus/geneticsABSTRACT
The expression of mammalian recombinant proteins in insect cell lines using transient-plasmid-based gene expression enables the production of high-quality protein samples. Here, the procedure for virus-free transient gene expression (TGE) in High Five insect cells is described in detail. The parameters that determine the efficiency and reproducibility of the method are presented in a robust protocol for easy implementation and set-up of the method. The applicability of the TGE method in High Five cells for proteomic, structural, and functional analysis of the expressed proteins is shown.
Subject(s)
Biotechnology/methods , Cloning, Molecular , Insecta/metabolism , Spike Glycoprotein, Coronavirus/biosynthesis , Transfection/methods , Animals , Bioreactors , Cell Culture Techniques/methods , Cell Line , Gene Expression , Glycosylation , Humans , Insecta/cytology , Mammals/genetics , Mammals/metabolism , Plasmids , Proteomics , Recombinant Proteins/biosynthesis , Recombinant Proteins/genetics , Reproducibility of Results , SARS-CoV-2/genetics , Spike Glycoprotein, Coronavirus/geneticsABSTRACT
The glycoprotein spike (S) on the surface of severe acute respiratory syndrome coronavirus (SARS-CoV-2) is a determinant for viral invasion and host immune response. Herein, we characterized the site-specific N-glycosylation of S protein at the level of intact glycopeptides. All 22 potential N-glycosites were identified in the S-protein protomer and were found to be preserved among the 753 SARS-CoV-2 genome sequences. The glycosites exhibited glycoform heterogeneity as expected for a human cell-expressed protein subunit. We identified masses that correspond to 157 N-glycans, primarily of the complex type. In contrast, the insect cell-expressed S protein contained 38 N-glycans, completely of the high-mannose type. Our results revealed that the glycan types were highly determined by the differential processing of N-glycans among human and insect cells, regardless of the glycosites' location. Moreover, the N-glycan compositions were conserved among different sizes of subunits. Our study indicates that the S protein N-glycosylation occurs regularly at each site, albeit the occupied N-glycans were diverse and heterogenous. This N-glycosylation landscape and the differential N-glycan patterns among distinct host cells are expected to shed light on the infection mechanism and present a positive view for the development of vaccines and targeted drugs.