Structural domains of the insulin receptor and IGF receptor required for dimerisation and ligand binding

We investigated structural requirements for dimerisation and ligand binding of insulin/IGF receptors, Soluble receptor fragments consisting of N-termi nal domains (L1/CYS/L2, L1/CYS/L2/F0) or fibronectin domains (F0/F1/F2, F1/ F2) were expressed in CHO cells. Fragments containing F0 or F1 domains were secreted as disulphide-linked dimers, and those consisting of L1/CYS/L2 do mains as monomers. None of these proteins bound ligand. However, when a pep tide of 16 amino acids from the alpha-subunit C-terminus was fused to the C -terminus of L1/CYS/L2, the monomeric insulin and IGF receptor constructs b ound their respective ligands with affinity only 10-fold lower than native receptors. (C) 2000 Federation of European Biochemical Societies.