Integrins are important extracellular matrix (ECM) receptor proteins located on cell surfaces. They are hetrodimers composed of an alpha and a beta transmembrane glycoprotein subunit. Around twenty two different integrins (different alpha/ beta subunit combinations) are found in nature. Integrins are generally present in high concentrations at the cell surface, but, unlike most other cell surface receptors, they bind ligands with very low affinity. Due to their weak individual binding, integrins need to cluster and bind in groups in order to effectively bind the ECM. Integrins bind many different ligands including laminin. Each integrin is made up of a large N terminal extracellular domain that binds the ECM ligand and a small C terminal cytoplasmic domain that mediates interaction with the actin cytoskeleton and signaling function. Alpha 1 integrin along with alpha 2, alpha L and alpha M has a unique inserted domain. Integrin alpha 1 is a receptor for laminin and collagen. The alpha1 subunit is also known as CD49a. CD49a associates with CD29 (beta 1 integrin), to form an alpha1 beta1 heterodimer, identified as the rat homologue to VLA1, which is involved in cellular adhesion to laminin and collagen.