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Integrins:

Integrins are one of the major classes of receptors within the ECM and mediate cell-ECM interactions with collagen, fibrinogen, fibronectin and vitronectin. Integrins provide essential links between the Extracellular environment and the intracellular signalling pathways which can play roles in cell behaviours such as apoptosis, differentiation, survival and transcription.

Integrins are heterodimeric; as they consist of an alpha and beta subunit. There are currently 18 alpha subunits and 8 beta subunits which combine to make up 24 different integrin combinations. Within each of the alpha and beta subunits there is a large extracellular domain, a transmembrane domain and a short cytoplasmic domain. The extracellular domain is where the ligand binds through the use of divalent cations. Generally Mn2+ increases affinity, Mg2+ promotes adhesion to cells and Ca2+ decreases cell adhesion. Integrins regulate their activity within the body by changing conformation. Most exist at rest in a low affinity state which can be altered to high affinity through an external antagonist which causes a conformational change within the integrin, increasing their affinity.

An example of this is the formation of platelets;


 * Antagonists such as thrombin or collagen trigger the integrin into its high affinity state which causes increased fibrinogen binding causing platelet aggregation.