The insulin receptor (Figure 23.15) is a glycoprotein with an 22 tetrameric structure, stabilized by disulfide bonds. Both the chain (735 residues) and the chain (620 residues) are translated from a single mRNA, giving a polypeptide chain that then undergoes proteolytic processing. The chain, which is thought not to span the membrane, is believed to bind insulin near its C-terminus. The chain has a transmembrane domain, with its C-terminus in the cell interior. The C-terminal region of the chain is the site of a protein tyrosine kinase activity, which is stimulated by the binding of insulin to the extracellular part of the receptor.

The kinase activity of insulin receptor is essential to its biological activity, because some cases of non-insulin-dependent diabetes are associated with receptor mutations that abolish the kinase activity.