The insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF1R) are highly related receptor tyrosine kinases with a disulfide-linked homodimeric architecture. Ligand binding to the receptor ectodomain triggers tyrosine autophosphorylation of the cytoplasmic domains, which stimulates catalytic activity and creates recruitment sites for downstream signalling proteins. Whether the two phosphorylated tyrosine kinase domains within the receptor dimer function independently or cooperatively to phosphorylate protein substrates is not known. Here we provide crystallographic, biophysical and biochemical evidence demonstrating that the phosphorylated kinase domains of IR and IGF1R form a specific dimeric arrangement involving an exchange of the juxtamembrane region proximal to the kinase domain. In this dimer, the active position of α-helix C in the kinase N lobe is stabilized, which promotes downstream substrate phosphorylation. These studies afford a novel strategy for the design of small-molecule IR agonists as potential therapeutic agents for type 2 diabetes.

Many proteins are modular in that they contain a series of independently‐folded domains. Often, these sub‐domains have no affinity for each other in solution, but can maintain a stable supertertiary structure when connected by polypeptide linkers. Little is known about the ultraweak interactions that dictate the stability of supertertiary structure. It is our hypothesis that surface features select for a specific structure, while the linker length determines the effective concentration thereby setting the interaction energy. To test this we attempted to redesign the multi‐domain scaffold protein PSD‐95. Structural studies have observed a stable supertertiary structure for the two N‐terminal PDZ domains from PSD‐95, but differing structural models were unable to identify interdomain interactions. We added a new interdomain salt bridge and linker extensions of varying rigidity. These manipulations rearranged the supertertiary structure but did not lead to isotropic motion of domains. This suggests that the forces stabilizing the structure are sufficient to withstand a 1.5‐fold decrease in effective domain concentration.Grant Funding Source: Supported by NIMH Grant MH081923