The type of protein that binds a ligand on the cell surface or within cells are transmembrane receptors. These proteins have 3 domains: an extracellular part that does the binding, a hydrophobic domain that extends through the membrane, and an intracellular region that transmits the signal. The most common membrane-anchored receptors are: G protein-coupled receptors, receptor tyrosine kinases, and ligand-gated ion channels.
