IRR: A Novel Member of the Insulin Receptor Family

Insulin’s effects, including its pivotal regulation of blood glucose levels, are mediated by a cell-surface receptor (reviewed in Olefsky, 1990; Ullrich and Schlessinger, 1990). The structure of the insulin receptor, defined using recombinant DNA techniques, exhibits a high degree of overall similarity with the receptor for the structurally related insulin-like growth factor (IGF), IGF-I (for review, see Czech, 1989). These heterotetrameric glycoproteins consists of extracellular a-subunits containing the insulin-binding region disulfide-bonded to β-subunits which span the membrane and contain a cytoplasmic tyrosine kinase activated by insulin binding (Ebina et al., 1985; Ullrich et al., 1985; Ullrich et al., 1986). The α-and β-subunits are derived by proteolytic cleavage of the proreceptor.