Receptor

A receptor is a protein — most often located at the cell surface, though nuclear and cytosolic receptors also exist — that binds a specific ligand and translates that binding event into a defined intracellular signal. Receptor families are typically distinguished by the mechanism of signal propagation: G-protein-coupled receptors (GPCRs), receptor tyrosine kinases, ligand-gated ion channels and nuclear receptors.

Receptors are defined pharmacologically by their ligand specificity, binding affinity, downstream effectors and the physiological system they control. The same ligand may engage several receptor subtypes with different affinities, and selectivity is a central design consideration for research peptides.