BRED: bioluminescence energy transfer to dye for monitoring ceramide trafficking in cell

Bioluminescence resonance energy transfer (BRET) is a genetically encoded proximity-based tool to study biomolecular interactions. However, conventional BRET is usually restricted to only a few types of interactions like protein-protein or protein-ligand interactions. We here developed a spatially unbiased resonance energy transfer system, so-called BRED - bioluminescence resonance energy transfer to dye. BRED allows transferring energy from a genetically encoded bright human optimized luciferase to a fluorophore-labelled small molecule. The high efficiency of the system allows RET without specific interaction of donor and acceptor. Here, we applied BRED to monitor the trafficking of the signalling lipid ceramide, to the Golgi. This was enabled by an engineered Golgi-resident luciferase, which was used to sense the influx of BODIPY-labeled ceramide into the surrounding membrane. We demonstrated the implementation of the method via flow cytometry, thereby combining the sensitivity of bulk cell methods with the advantages of single-cell analysis. This toolbox enables simple and robust live-cell analysis of inhibitors of CERT-mediated ceramide transport. The design principle of our optogenetic tool can be applied to study intracellular trafficking of metabolites and screen for inhibitors of their key enzymes.