A single-chain insulin-like growth factor I/insulin hybrid binds with high affinity to the insulin receptor.

1. To investigate the structure/function relationship of the interaction between ligand and receptor in the insulin-like growth factor I (IGF-I) and insulin receptor systems we have prepared and characterized a single-chain insulin/IGF-I hybrid. The single-chain hybrid consists of 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 soluble insulin receptors and membrane-bound holoreceptors. The affinity for interacting with the soluble truncated insulin receptors was 55-94% relative to insulin, and affinity for membrane-bound insulin receptors was 113% of that of insulin. Furthermore we found that the affinity 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 ligand. This indicates that coordinately changing domains of the receptors and the ligands can induce higher affinity of ligand for receptor, supporting the idea that these receptors have a common ligand-binding site [Kjeldsen, Andersen, Wiberg, Rasmussen, Schäffer, Balschmidt, Møller and Møller (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 4404-4408]. 3. In contrast with what was generally assumed about the ligand structure required for binding to the insulin receptor we demonstrate the first single-chain insulin analogue that can bind with high affinity to the insulin receptor.