Seminar

Real-time chemical tools to capture and control sugar signaling in cells

Charlie Fehl

All cells use glucose. One important role of this ubiquitous sugar is to chemically regulate cellular metabolism by remodeling intracellular signaling proteins with glycans in real-time response to cell conditions. As an example, hyperglycemia is strongly correlated with risk factors for cancer and diabetes, two disease types with “hallmark” aberrant glycosylation patterns. However, intracellular glycosylation processes are intrinsically challenging to study in real time due to the rapid and variable rate of sugar metabolite utilization and a lack of intracellular tools. We approach this challenge by building technology and novel experimental strategies to allow chemical control over sugar-based signaling pathways, especially O-linked N- acetylglucosamine modification of proteins (O-GlcNAcylation), a glucose-derived modification involved in signaling. We use two complimentary technologies to enable chemical control over O-GlcNAc labeling: photochemistry and O-GlcNAc-directed proximity labeling. Our photochemical methods enable “turn-on” GlcNAc reporters and photoredox strategies for light-triggered labeling in cells. Our proximity labeling methods create targeted biosensors that can be initiated to “tag” O-GlcNAc proteins in live cells by fusing GlcNAc-binding domains to labeling systems, a strategy we call “GlycoID.” We apply our photochemical and GlycoID platforms to study spatiotemporal effects of signaling (insulin) and hyperglycemic metabolism on cellular O-GlcNAc pathways, physiological states that re-wire O-GlcNAcylation patterns in cells. Our tools reveal real-time and spatial insights into O-GlcNAc glycobiology and reveal features that bridge physiology and disease. A key example is how O-GlcNAcylation of TET1 helps explain, in part, how obesity-linked hyperglycemia enhances tumorigenesis in early-onset breast cancers.