The integrin family

Publisher Summary This chapter discusses the biological function and receptor–ligand interactions of integrin family of adhesion receptors. The integrins are a widely distributed family of noncovalent heterodimeric glycoproteins that connect their extracellular ligands with the cytoskeleton. The β subunits are 40–48% homologous, and the members are most commonly separated into subgroups based on the β subunit. The best-studied integrins are the β1 (originally called the “very late antigens” ), the β2 (or leukocyte integrins), and the β3 families, although eight different β subunits have now been characterized. Several of the β subunits can form heterodimers with different a subunits, and some a subunits can complex with several β subunits. Heterodimer formation is required for ligand binding, and evidence suggests that each subunit participates in determining ligand specificity. The ligands recognized by the integrins broadly mediate either cell–cell interactions or cell–extracellular matrix interactions. The important role of integrins in biological systems is exemplified by the identification of pathological conditions because of their deficiency or dysfunction. One feature that distinguishes integrins from other adhesion receptors is the regulation of the affinity of their interactions with ligands. This dynamic process, often referred to as “affinity modulation,” allows rapid fluctuations between inactive (low affinity) and active (high affinity) states.