Functional Properties of a Naturally Occurring Trp1200 → Ser1200 Mutation of the Insulin Receptor

Based on the sequence of cDNA encoding the intracellular domain of the insulin receptor β-subunit, we recently defined a heterozygous point mutation causing a Ser for Trp substitution at position 1200 in the tyrosine kinase domain of a patient (BI-2) with the type A syndrome of insulin resistance. We have now sequenced the remainder of Bl-2's insulin receptor cDNA-coding region and find no additional alterations in the encoded proreceptor protein. The nucleotide sequence of cDNA encoding the portion of the β3-subunit which includes Trp1200 was normal in Bl-2's unaffected mother. Hybridization of a mutant allele-specific oligonucleotide to polymerase chain reaction-amplified cDNA confirmed the presence of the mutant allele in the proband and excluded it in her unaffected sister and mother, 18 normal control subjects, and six other subjects with insulin resistance. To determine whether this mutation had functional consequences for receptor signalling, we reconstructed it into a full-length insulin receptor ...