Structural basis of insulin receptor antagonism by bivalent site 1-site 2 ligands S961 and Ins-AC-S2.

Summary

Cryo-EM structures demonstrate that S961 and Ins-AC-S2 antagonize the insulin receptor by stabilizing an inactive conformation. The order of site-1/site-2 modules dictates agonism versus antagonism, and distinct αCT and FnIII-2/insert domain interactions differentiate S961 from Ins-AC-S2, informing rational design of next-generation antagonists for congenital hyperinsulinism.

Key Findings

• Cryo-EM structures show S961 and Ins-AC-S2 bind and stabilize an inactive insulin receptor conformation.
• Agonist vs antagonist activity depends on the order of site-1 and site-2 modules in bivalent ligands.
• S961 and Ins-AC-S2 differ in αCT displacement/engagement and in interactions with receptor FnIII-2/insert domains.

Clinical Implications

While preclinical, these structures enable structure-guided optimization of insulin receptor antagonists, potentially improving efficacy and safety profiles for congenital hyperinsulinism where therapeutic options are limited.

Limitations

• Preclinical structural study without in vivo pharmacology or safety data
• Generalizability to other ligand classes remains to be tested

Future Directions

Use these structures to engineer optimized antagonists, validate in animal models of congenital hyperinsulinism, and explore structure–activity relationships across additional bivalent scaffolds.