Allosteric (effect)

An allosteric effect typically results from a drug binding to a target protein at a site different from the agonist binding site, and (presumably) causing a shape change in the protein. This shape change does not necessarily have a direct effect on the protein’s behaviour (although it is possible to cause direct activation of a receptor by an allosteric ligand). More usually, the presence of the allosteric ligand modifies the protein’s responses to the binding of agonists or antagonists at the usual agonist binding site on the protein. Binding affinity may be increased or decreased, or agonist efficacy may be enhanced or reduced. For example, binding of benzodiazepines (such as diazepam) to the GABA_A receptor doesn’t stimulate the receptor directly, but rather enhances the response of the receptor to binding of the natural agonist, GABA.