Exploiting bacterial toxins in characterizing extracellular interactions

Established protein-protein interaction assays, such as yeast two-hybrid assay or AP-MS, have been powerful technologies in characterizing interactions between soluble intracellular proteins. Where they fall short, however, are interactions between transmembrane receptors and their ligands. Currently, there are no easily scalable methods for studying receptor/ligand interactions in an unbiased fashion. Thus, identifying ligand/receptor pairs has remained challenging and, consequently, a substantial fraction of known transmembrane receptors and soluble ligands remain orphans. We have established a platform that combines the receptor specificity and modularity of bacterial exotoxins with the power of genome-wide CRISRPR/Cas9 screens to characterize receptors for secreted proteins in an unbiased manner. Our approach can identify native receptors and downstream trafficking factors for diverse extracellular proteins and even their posttranslational modifications. Using a similar approach, we have also discovered previously unknown receptors for native bacterial toxins, including a novel receptor for a large clostridial toxin from C. sordellii, a human pathogen.