Insulin Receptor Family

The Insulin (IR) family consists of IR, the insulin-like growth factor I-receptor (IGF-IR) and the insulin receptor-related receptor (IRR). The IR subfamily is an exception in the receptor tyrosine kinase (RTK) superfamily in that it exists as a covalent disulfide-linked dimer (with a low basal activity kinase) in the absence of ligand. In other words, IR subfamily members are also expressed as a single subunit, but they undergoes processing into form two, α and β, polypeptide chains that are assembled into a heterotetramer, or an (αβ)2 homodimer, stabilized by disulfide bonds. Interestingly, the covalently disulfide-linked (αβ)2 hybrid dimeric receptor (IR::IGF-IR) composed of an IR αβ hemireceptor and an IGF-IR αβ hemireceptor, , which bind preferentially IGF-1 and IGF-2 over insulin.