Receptors: Structure and function

Receptor proteins are responsible for the selective action of a multitude of regulatory factors that include circulating peptide and steroid hormones, as well as odorants, photons, and toxins. Specificity in the action of these ligands owes most directly to the receptor proteins themselves, which, as a result of their localization to discrete populations of cells, restrict responses to their target tissues. Although the structure of receptors varies considerably between their classes, key functions of these proteins are universal. These include structural specificity in their ligand binding sites, as well as conformational changes that result from ligand binding. The latter serves, directly or indirectly, to modulate the activity of a specific effector, which in turn regulates a signaling pathway leading to phenotypic changes that typify the ligand. Genetic or acquired modifications of receptor proteins result in a diverse set of diseases that will be discussed in subsequent articles in this series.