The Purified COOH-Terminal Domain of the Insulin Receptor Carries Activity to Stimulate Protein Kinase Activity or Autophosphorylation of the β Subunit Domain of Insulin Receptor

Abstract

Our previous study using a deletion mutant indicated that the COOH-terminal (CT) domain of the insulin receptor plays important roles in both catalytic efficiency and stability of the receptor kinase (Yan et al., J. Biol. Chem., 268 [1993] 22444). In this study, we purified the CT domain of 98 amino acids from bacterial cells over-expressing the CT domain and examined its effect on insulin and IGF-I receptor protein kinases. The purified CT domain stimulated the kinase activities of purified insulin receptor-transmembrane/cytoplasmic domain (IRTMTPK) and its CT domain-deletion mutant (IRTMTPKΔCT), 3.3-fold and 2.3-fold, respectively, while it was less effective in stimulating the kinase activity of purified IGF-I receptor transmembrane/ cytoplasmic domain (IGFIRTMTPK) (1.4-fold). When the effect of the CT domain on autophosphorylation was examined, a marked increase in autophosphorylation was observed only with IRTMTPKΔCT, These results suggest that the CT domain specifically interacts with the insulin receptor cytoplasmic domain, thereby activating the kinase or autophosphorylation activity.