An insulin receptor mutant (Asp(707)->Ala), involved in leprechaunism, is processed and transported to the cell surface but unable to bind insulin

Abstract

We have identified a homozygous mutation near the carboxyl terminus of the insulin receptor (IR) alpha subunit from a leprechaun patient, changing Asp(707) into Ala, Fibroblasts from this patient had no high affinity insulin binding sites, To examine the effect of the mutation on IR properties, the mutant IR was stably expressed in Chinese hamster ovary cells, Western blot analysis and metabolic labeling showed a normal processing of the mutant receptor to alpha and beta subunits, No increase in high affinity insulin binding sites was observed on Chinese hamster ovary cells expressing the mutant receptor, and also, affinity cross-linking of I-125-labeled insulin by di-succinimidyl suberate to these cells failed to label the mutant alpha subunit, Biotinylation of cell surface proteins by biotin succinimidyl ester resulted in efficient biotinylation of the mutant IR alpha and beta subunits, showing its presence on the cell surface, On solubilization of the mutant insulin receptor in Triton X-100-containing buffers, I-125-insulin was efficiently cross-linked to the receptor alpha subunit by disuccinimidyl suberate,