Insulin receptor β subunit autophosphorylation occurs in an intramolecular trans-reaction in which one β subunit phosphorylates the adjacent β subunit within an α2β2 holoreceptor complex (Frattali, A. L., Treadway, J. L., and Pessin, J. E. (1992) J. Biol. Chem. 267, 19521-19528). To determine the spatial relationship between α subunit occupancy and β subunit autophosphorylation, the vaccinia virus/bacteriophage T7 transient expression system was used to generate insulin/insulin-like growth factor (IGF)-1 hybrid receptors. The extent of hybrid receptor formation was proportional to the molar ratio of the insulin and IGF-1 receptor expression plasmids used for transfection of cultured fibroblasts. Insulin/IGF-1 hybrid receptors displayed high affinity binding for insulin and IGF-1 similar to that observed for homotypic insulin and IGF-1 receptors, respectively. As expected, insulin poorly competed for 125I-IGF-1 binding to the insulin/IGF-1 hybrid receptors compared with IGF-1. IGF-1, however, competed more efficiently than insulin for 125I-insulin binding, indicating interactions between the α subunit binding sites. Furthermore, insulin or IGF-1 stimulated the autophosphorylation of both β subunits within wild type insulin/IGF-1 hybrid receptors. Ligand-stimulated autophosphorylation of two different mutant/wild type insulin/IGF-1 hybrid receptors also resulted in the labeling of each β subunit independent of which α subunit was occupied with ligand. These data demonstrate that insulin/IGF-1 hybrid receptors bind both ligands with high affinity and that occupancy of either α subunit results in a series of intramolecular trans-autophosphorylation reactions between β subunits.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - 1993|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology