The insulin receptor is a heterotetrameric membrane glycoprotein with tyrosine-protein kinase activity, consisting of disulfide-linked subunits in a beta-alpha-alpha-beta configuration. The beta subunit possesses a single transmembrane domain, whereas the alpha subunit is completely extracellular. The alpha chains contribute to the formation of the ligand-binding domain, while the beta chains carry the kinase domain. Binding of insulin to the insulin receptor stimulates its association with downstream mediators including IRS1 and phosphatidylinositol 3'-kinase (PI3K) which leads to glucose uptake. Two transcript variants encoding different isoforms have been found for this gene produced by alternative splicing.