Integrin activation: the link between ligand binding and signal transduction.

A major function of the integrin family of receptors is to provide a physical connection between extracellular adhesion proteins and intracellular cytoskeletal/signalling molecules. These linkages are dynamic and are influenced in a bidirectional manner by changes in the microenvironment of the plasma membrane that occur both inside and outside of cells. The mechanisms employed by integrins to transduce information are complex, but a series of recent studies has clarified their molecular basis. In particular, explanations for the interdependence of ligand binding, occupancy by divalent cations and receptor conformation have been obtained, and some of the key sites responsible for each property have been localized within the integrin heterodimer. These insights now permit a better visualization of the intricate molecular switch that controls the adhesive phenotype.