RESEARCH SUMMARY Glycans and proteins interact on the cell membrane affecting the general characteristics and behavior of the cell. The nature of glycan-protein interactions is of fundamental interests to biology, however elucidating this interaction in live cells has been strictly limited. Crosslinking technology has advanced and has been used to understand the fundamental of protein-protein interactions. These methods employ many new crosslinking reagents and have further been aided by the significant progress in rapid throughput proteomic methods. While most membrane proteins are glycosylated, glycan-protein crosslinking experiments are rare and limited by the dearth of glycan specific crosslinking reagents as well as limitations in glycomic and glycoproteomic analytical methods. This research will develop glycan-protein crosslinking reagents for use in live cells. It further takes advantage of bioorthogonal reagents that allows the incorporation of modified monosaccharides into the cell's metabolic pathway producing chemically modified glycans in cell membrane. The incorporation and efficiencies of the syntheses and crosslinking reactions are monitored by new glycomic and glycoproteomic analytical methods. The modified glycans are used to tether crosslinking reagents that react with target proteins. The method identifies the glycopeptide as well as the crosslink target protein providing unprecedented views of the role of glycans in protein-protein interactions. 1