Orphan Receptor

Orphan receptors refer to receptor proteins for which no endogenous ligands have yet been identified. They are widely found in superfamilies such as G protein-coupled receptors (GPCRs), nuclear receptors (NRs), and receptor tyrosine kinases (RTKs). These receptors possess a complete structure, including ligand-binding domains, transmembrane domains, and intracellular signalling domains; however, their functions remain poorly understood. They are often associated with embryonic development, metabolic regulation, inflammation, and tumourigenesis.