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An insulin receptor is a dimer of heterodimers. The dimers are noncovalent, but the insulin receptors are covalently maintained as functional dimers by disulfide bonds. An insulin receptor is comprised of 2 α-chains, and 2 β-chains. The α-chain and an estimated 190 residues of the β-chain are located on the extracellular side of the plasma membrane. The rest of the beta-chain consists of a single transmembrane helix, the juxtamembrane domain, and the intracellular tyrosine kinase domain.  

The alpha subunits are the site for insulin binding. Each subunit is comprised of 2 Leucine rich domains (L1 and L2), a Cysteine rich domain (CR) and an α-chain C-terminal helix (α-CT). The two subunits are held together by a disulfide bond between the cysteine rich domains.  

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Due to the heterodimeric nature of the receptor, there are two types of insulin binding sites that are split into pairs in the alpha subunits: sites 1 and 1' and sites 2 and 2', for a total of 4 binding sites of insulin. Binding sites 1 and 1' have a greater surface area and are more easily accessible for the insulin to bond, resulting in a higher affinity for insulin binding. Binding sites 2 and 2' have less surface area and are located on the back of the beta sheet so their binding sites do not get filled as quickly.  

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