Identification of a Ligand-Binding Region of the Human Insulin Receptor Encoded by the Second Exon of the Gene

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Abstract
Structure-function studies of the insulin molecule indicate that an insulin B chain domain comprising residues 22–26 is involved both in binding to the insulin receptor (INSR) and in insulin dimer formation, suggesting that this domain might also interact with a structure resembling the insulin dimer interface in the INSR. Expression of a mutant INSR cDNA with a deletion of the region corresponding to exon 2 of the INSR gene produces a protein devoid of insulin-binding activity, although the mutant protein is processed appropriately to α- and β-subunits, suggesting that the insulin-binding domain is encoded at least in part by exon 2. Within this region of the INSR molecule, the sequence 83–103 fulfills the structural criteria for a dimer interface. Studies of mutant INSRs with substitutions for phenylalanine 88 or 89 show that the presence of phenylalanine at position 89 is essential for full binding affinity.

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