Title:  Design of Extracellular Peptide-Ligand Dimerization Actuator Receptors for Programming Cell Behavior
Over the past three decades synthetic biologists have taken a page from nature’s playbook and developed synthetic cell-surface receptors that sense extracellular inputs and convert these signals into user-defined cellular responses. Perhaps one of the most exciting examples of this is the development of CAR (chimeric antigen receptor) T-cell therapy which endows immune cells with the ability to identify and fight cancer. In this seminar, I will first go over different types of synthetic cell-surface receptors with a focus on their clinical applications and limitations. I will then overview how we used a ‘design-build-test-learn’ approach to develop and characterize the extracellular and intracellular domains of EPDA (Extracellular Peptide-Ligand Dimerization Actuator) cell-surface receptors. Extracellularly, Stimulatory and Inhibitory EPDA receptors rapidly dimerize with high specificity upon coming in contact with their peptide-ligand counterparts.  Intracellularly, dimerized Stimulatory EPDA receptors phosphorylate substrates that merge split GFP (green fluorescent protein) halves, and dimerized Inhibitory EPDA receptors dephosphorylate substrates leading to GFP separation. Cells programmed with EPDA cell-surface receptors can rapidly and reversibly actuate green fluorescence, and by substituting split GFP with dCas9 the transcription of user-defined genes can be regulated. This synthetic platform enables Mammalian cells to communicate with peptide-ligands and opens exciting avenues of research including the development of ‘living’ materials and synthetic autocrine signaling for regulating therapeutic outputs during cell therapy.