Characterization of Cell Surface Glycoproteins Using Enzymatic Treatment and Mass Spectrometry

Almost all proteins on the cell surface are modified by glycosylation. Cell surface glycoproteins participate in various cellular pathways, such as cell adhesion, cell–cell communication, and immune response. Due to their functional importance, glycoproteins on the cell surface often serve as potential therapeutic targets. Recent advancements in mass spectrometry (MS) have facilitated the characterization of glycoproteins that are generally localized on the cell surface, secreted to the extracellular environment, or found in intracellular organelles such as the endoplasmic reticulum, Golgi apparatus, and peroxisome. However, the selective characterization of glycoproteins on the cell surface remains challenging. In this study, we applied enzymatic treatment to live cells, followed by MS-based glycoproteomics analysis, to assess changes in protein glycosylation at different treatment time points as a method to identify cell surface glycoproteins. To demonstrate this approach, a renal cell carcinoma cell line, A498, was treated with glycosidases, sialidase and PNGase F, over two treatment time intervals, 2 and 24 h. Glycoproteins were identified as cell surface glycoproteins from A498 cells when enzyme treatment altered the glycosylation of the glycoproteins. The results revealed the effectiveness of integrating enzymatic treatment with MS-based glycoproteomics for analyzing cell surface glycoproteins. Our established method has demonstrated the potential applications for assessing accessibility of therapeutic targets on the cell surface over time and supporting the development of new targeted therapies.