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Structural basis of insulin receptor antagonism by bivalent site 1-site 2 ligands S961 and Ins-AC-S2 | Nature Communications
Congenital hyperinsulinism is a rare genetic disease characterized by overproduction of insulin. One class of potential treatments is insulin receptor antagonists like S961 and Ins-AC-S2, which comprise segments for binding each of the two insulin-binding sites (site 1 and site 2) on the receptor. Notably, S597 – containing the same receptor binding segments as S961 but in the opposite order (site 2-site 1) – is an insulin receptor agonist rather than an antagonist. Using cryo-EM, we show how both S961 and Ins-AC-S2 bind an inactive conformation of the receptor, thereby explaining their antagonism. Furthermore, our structures reveal how agonist vs. antagonist activity is influenced by the order of site 1- and site 2-binding modules in bivalent ligands. Additionally, we show subtle differences between the receptor-binding mechanisms of S961 and Ins-AC-S2, which include displacement or engagement of αCT, and a binding interface between the Ins-AC-S2 insulin and the receptor FnIII-2/inser
