Vulnerabilities in coronavirus glycan shields despite extensive glycosylation

“…At the same time, the MERS-CoV S1 protein exhibited a significantly lower amount of complex glycan type (MERS-CoV, 44.11% vs SARS-CoV-1, 81.08% vs SARS-CoV-2, 89.32%). However, this result may appear contradictory to other recent works by Watanabe et al and Zhao et al. This incongruity is anticipated due to differences in the scope of the studies.…”

“…However, this result may appear contradictory to other recent works by Watanabe et al. ( 26 ) and Zhao et al ( 14 ) This incongruity is anticipated due to differences in the scope of the studies. The current work investigates the isomeric glycosylation of the S1 subunit of the S protein, while the other two studies explore glycosylation in both S1 and S2 subunits.…”

“…With 23, 23, and 22 N-linked glycan sites per monomer for MERS, SARS-CoV, and SARS-CoV-2, respectively, extreme heterogeneity is expected within each spike protein trimer, as has been confirmed in the literature from analytical characterization of these proteins. ,,,,− This heterogeneity is also demonstrated by the broad mass profiles observed from I 2 MS measurements, with fwhm values of 14.6, 14.0, and 13.4 kDa, respectively, for MERS, SARS-CoV, and SARS-CoV-2 spike protein trimers. While these fwhm values alone are only an indicator of glycan heterogeneity, we also used previously published site-specific glycan structure results from bottom-up glycopeptide analysis of these same three spike protein trimers , to interrogate the theoretical distribution of protein mass for each spike protein using a Monte Carlo approach, similar to that previously published .…”

“…For other antibodies (LSI-CoVA-014/LSI-CoVA-015/LSI-CoVA-016/5A6) the primary binding sites were non-glycosylated epitopes, as identified by HDXMS, with only secondary interactions contributed by glycans. These results provide a view contrary to the prevailing notion that glycans only act as a shield for Spike protein to hide epitope sites from host immune recognition 42 , 43 and suggest that non-specific interactions of glycans with the antibodies can play a substantial role in stabilizing Fab arm binding at the epitope site.…”