Dissecting the Heterogeneous Glycan Profiles of Recombinant Coronavirus Spike Proteins with Individual Ion Mass Spectrometry

• Published in: Journal of the American Society for Mass Spectrometry 2024-01, Vol.35 (1), p.62-73
• Main Authors: Stiving, Alyssa Q., Foreman, David J., VanAernum, Zachary L., Durr, Eberhard, Wang, Shiyi, Vlasak, Josef, Galli, Jennifer, Kafader, Jared O., Tsukidate, Taku, Li, Xuanwen, Schuessler, Hillary A., Richardson, Douglas D.
• Format: Article
• Language: English
• Subjects: Humans; Mass Spectrometry - methods; Polysaccharides - analysis; Spike Glycoprotein, Coronavirus - chemistry; Vaccines
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1021/jasms.3c00309

Surface-embedded glycoproteins, such as the spike protein trimers of coronaviruses MERS, SARS-CoV, and SARS-CoV-2, play a key role in viral function and are the target antigen for many vaccines. However, their significant glycan heterogeneity poses an analytical challenge. Here, we utilized individual ion mass spectrometry (I2MS), a multiplexed charge detection measurement with similarities to charge detection mass spectrometry (CDMS), in which a commercially available Orbitrap analyzer is used to directly produce mass profiles of these heterogeneous coronavirus spike protein trimers under native-like conditions. Analysis by I2MS shows that glycosylation contributes to the molecular mass of each protein trimer more significantly than expected by bottom-up techniques, highlighting the importance of obtaining complementary intact mass information when characterizing glycosylation of such heterogeneous proteins. Enzymatic dissection to remove sialic acid or N-linked glycans demonstrates that I2MS can be used to better understand the glycan profile from a native viewpoint. Deglycosylation of N-glycans followed by I2MS analysis indicates that the SARS-CoV-2 spike protein trimer contains glycans that are more difficult to remove than its MERS and SARS-CoV counterparts, and these differences are correlated with solvent accessibility. I2MS technology enables characterization of protein mass and intact glycan profile and is orthogonal to traditional mass analysis methods such as size exclusion chromatography–multiangle light scattering (SEC-MALS) and field flow fractionation–multiangle light scattering (FFF-MALS). An added advantage of I2MS is low sample use, requiring 100-fold less than other methodologies. This work highlights how I2MS technology can enable efficient development of vaccines and therapeutics for pharmaceutical development.