Site‐Specific and Multiple Fluorogenic Metabolic Glycan Labeling and Glycoproteomic Profiling in Live Cells

Multicolor labeling for monitoring the intracellular localization of the same target type in the native environment using chemical fluorescent dyes is a challenging task. This approach requires both bioorthogonal and biocompatible ligations with an excellent fluorescence signal‐to‐noise ratio. Here, we present a metabolic glycan labeling technique that uses homemade fluorogenic dyes to investigate glycosylation patterns in live cells. These dyes allowed us to demonstrate rapid and efficient simultaneous multilabeling of glycoconjugates with minimum fluorescence noise. Our results demonstrate that this approach is capable of not only probing sialylation and GlcNAcylation in cells but also specifically labeling the cell‐surface and intracellular sialylated glycoconjugates in live cells. In particular, we performed site‐specific dual‐channel fluorescence imaging of extra and intracellular sialylated glycans in HeLa and PC9 cancer cells as well as identified fluorescently labeled sialylated glycoproteins and glycans by a direct enrichment approach combined with an MS‐based proteomic analysis in the same experiment. In conclusion, this study provides multilabeling tools in cellular systems for simultaneous site‐specific glycan imaging and glycoproteomic analysis to study potential cancer‐ and disease‐associated glycoconjugates. We demonstrated a multi‐fluorescent MGL strategy combining ZIC‐cHILIC StageTip enrichment and subsequent LC–MS/MS analysis for live cell glycan labeling and glycoprotein profiling in a single experiment. This approach enables the simultaneous site‐specific labeling of cell‐surface and intracellular sialylated glycoconjugates, global profiling, and identification of sialylated glycoproteins and glycans.