A SINGLE-CHAIN INSULIN-LIKE GROWTH-FACTOR-I INSULIN HYBRID BINDS WITHHIGH-AFFINITY TO THE INSULIN-RECEPTOR

1. To investigate the structure/function relationship of the interacti on between ligand and receptor in the insulin-like growth factor I (IG F-I) and insulin receptor systems we have prepared and characterized a single-chain insulin/lGF-I hybrid. The single-chain hybrid consists o f the insulin molecule combined with the C domain of IGF-I. The single -chain hybrid was found to bind with high affinity to both truncated s oluble insulin receptors and membrane-bound holoreceptors. The affinit y for interacting with the soluble truncated insulin receptors was 55- 94% relative to insulin, and the affinity for membrane-bound insulin r eceptors was 113% of that of insulin. Furthermore we found that the af finity of the single-chain hybrid molecule for IGF-I receptors was 19- 28% relative to IGF-I. 2. The affinity of the single-chain hybrid for chimeric insulin/IGF-I receptors exceeded that of either natural ligan d. This indicates that coordinately changing domains of the receptors and the ligands can induce higher affinity of ligand for receptor, sup porting the idea that these receptors have a common ligand-binding sit e [Kjeldsen, Andersen, Wiberg, Rasmussen, Schaffer, Balschmidt, Moller and Moller (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 4404-4408]. 3. In contrast with what was generally assumed about the ligand structure r equired for binding to the insulin receptor we demonstrate the first s ingle-chain insulin analogue that can bind with high affinity to the i nsulin receptor