Abstract
Tick-borne encephalitis virus (TBEV) is the causative agent of severe human neuroinfections that most commonly occur after a tick bite. N-Glycosylation of the TBEV envelope (E) glycoprotein is critical for virus egress in mammalian cells, but not in tick cells. In addition, glycans have been reported to mask specific antigenic sites from recognition by neutralizing antibodies. In this regard, the main purpose of our study was to investigate the profile of N-glycans linked to the E protein of TBEV when grown in human neuronal cells and compare it to the profile of virus grown in tick cells. Mass spectrometric analysis revealed significant differences in these profiles. High-mannose glycan with five mannose residues (Man5GlcNAc2), a complex biantennary galactosylated structure with core fucose (Gal2GlcNAc2Man3GlcNAc2Fuc), and a group of hybrid glycans with the composition Gal0-1GlcNAc1Man3-5GlcNAc2Fuc0-1 were confirmed as the main asparagine-linked oligosaccharides on the surface of TBEV derived from human neuronal cells. The observed pattern was supported by examination of the glycopeptides, providing additional information about the glycosylation site in the E protein. In contrast, the profile of TBEV grown in tick cells showed that paucimannose (Man3-4 GlcNAc2Fuc0-1) and high-mannose structures with five and six mannoses (Man5-6GlcNAc2) were major glycans on the viral surface. The reported results complement existing crystallography and cryoelectron tomography data on the E protein structure and could be instrumental for designing carbohydrate-binding antiviral agents active against TBEV.
Highlights
Tick-borne encephalitis virus (TBEV) is the causative agent of severe human neuroinfections that most commonly occur after a tick bite
We employed the MALDI-mass spectrometric (MS) technique to thoroughly investigate N-glycans of the E glycoprotein isolated from TBEV grown in human and tick (IRE/CTVM19) cells, and N-glycans from uninfected cells of the same types
In the case of TBEV grown in neuronal cells, the purified E glycoprotein underwent digestion with trypsin, and isolated glycopeptides were evaluated to validate the glycosylation pattern and confirm a glycosylation site in the protein
Summary
Tick-borne encephalitis virus (TBEV) is the causative agent of severe human neuroinfections that most commonly occur after a tick bite. Glycans have been reported to mask specific antigenic sites from recognition by neutralizing antibodies In this regard, the main purpose of our study was to investigate the profile of N-glycans linked to the E protein of TBEV when grown in human neuronal cells and compare it to the profile of virus grown in tick cells. Deletion of the glycosylation site of the E protein had no effect on the growth of TBEV in tick cells This may be associated with different TBEV maturation processes seen in mammalian and tick cells[18]. Despite the fact that TBEV E protein has been characterized extensively, including determination of its structure using X-ray crystallography[21] and cryoelectron tomography (cryo-EM)[22], the precise compositions of N-glycans attached to TBEV E protein derived from mammalian and tick hosts remain unknown. Since the glycosylation pattern can have a large impact on virus properties, including pathogenicity and v irulence[10], this needs to be further addressed
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