Institute of Science and Technology Austria (IST Austria)
Optical functionalization of human Class A orphan G-protein coupled receptors
G-protein coupled receptors (GPCRs) relay environmental stimuli to regulate diverse cellular functions and are prime drug targets. One third of the human GPCRs are classified as orphans because of limited information on their ligands and coupling to the cellular signaling machinery. By creating fusion proteins with rhodopsin we re-engineered 64 human orphan GPCRs (all but one unassigned orphan GPCR currently listed by the International Union of Basic and Clinical Pharmacology) to be activated by visible light in the absence of their unknown ligands. With this approach, we identified activation of canonical cell signaling pathways, including cAMP-, Ca2+-, MAPK/ERK- and Rho-dependent pathways, downstream of a subset of orphan GPCRs. This subset includes the human pseudogene GPR33, whose optically-resurrected function supports the hypothesized role of this receptor as a pathogen entry site. Sequence evolution analysis revealed evidence of purifying selection in the ligand-binding domains of functional orphan GPCRs, signifying the importance of their sensory domains and the likely existence of ligands. Light-activation will permit further studies on the function of orphan GPCRs and their potential as therapeutic targets.