ABSTRACT - “Chemical Tools for the Investigation and Manipulation of Protein Glycosylation” The broad goal of this proposal is the development of chemical tools that will enable the facile and robust identification and inhibition of glycosylation in specific cells, the mapping of glycosylation-mediated and cell- type specific interactions, and monitoring and manipulation of carbohydrate biosynthetic pathways. The addition of carbohydrates to proteins, or glycosylation, is one of the most common forms of posttranslational modifications and is associated with various processes, including protein stability, macromolecular interactions, and cellular signaling. Unfortunately, the currently available tools for interrogating these functions fall short, which limits the study of glycosylation to expert labs. We plan to tackle this unmet need using carbohydrate chemistry, photo-chemistry, and chemical biology in three specific aims. In Aim 1, we will build on our development of glycosylation probes and inhibitors, with a focus on using chemical genetic approaches to create tools to identify and perturb glycosylation in a cell-specific fashion. In Aim 2, we will leverage the advantages of chemoenzymatic modification of glycosylation to install specific photocrosslinkers onto living cells, with a focus on identifying biological interactions that are mediated by glycans, as well as mapping cell interactions. Finally, in Aim 3, we will create novel activity-based probes for measuring and inhibiting critical enzymes responsible for monosaccharide biosynthesis. At the conclusion of these independent aims, we will have generated new powerful tools that will have an immediate impact on the types of questions scientists can ask about glycosylation in human health and disease.