Receptors

Abstract

The transduction of an extracellular signal inside the cell, and triggering of complex eukaryotic signaling machinery, in many instances begins with binding of a specific ligand to its specific plasma membrane receptor. Mechanisms for transduction of signals across the plasma membrane are various and determine structural diversity of different groups of receptors. They can be divided into two main groups. The first one includes receptors that possess intrinsic catalytic activity or ion-channel activity. These constructions can be considered as enzymes or ion channels with additional domains necessary for agonist binding. In many instances such receptors contain an accessory hydrophobic transmembrane domain which is responsible for proper orientation of the molecule and transduction of received signal across the plasma membrane. Binding of the agonist results in complex structural rearrangements of the receptor molecule, which resolve in alterations of receptor enzymatic activity or in changes of membrane permeability for certain ions. The second group contains receptors which are enzymatically non-active, but structurally linked with downstream signaling complexes. Such receptors are composed of sensory, transmembrane and specialized intracellular domains. The latter most often were shown to be implicated in transduction of an extracellular signal to coupled intracellular signal transducing molecule(s).