ECM cell surface receptors: Integrin (Pt. 2)

Integrins are crucially important because they are the main receptor proteins that cells use to both bind to and respond to the ECM. Integrins differ from cell-surface receptors for other extracellular soluble signal molecules in that they usually bind their ligand with lower affinity and are present 10-100 higher concentration on the cell surface. If the binding were too tight, cells would become irreversibly glued to the matrix and would be unable to move. In some way integrin binding resembles “Velcro”. Integrins also activate intracellular signalling pathways that communicate to the cell the character of the ECM that is bound. There are multiple types of α and β subunits, resulting in many types of integrin heterodimers. Many integrins recognize the RGD sequences in the adhesive glycoproteins such as Laminin and Fibronectin. Integrin tails interact with cytosolic proteins that link integrins to intracellular cytoskeleton.