THE PURIFIED COOH-TERMINAL DOMAIN OF THE INSULIN-RECEPTOR CARRIES ACTIVITY TO STIMULATE PROTEIN-KINASE ACTIVITY OR AUTOPHOSPHORYLATION OF THE BETA-SUBUNIT DOMAIN OF INSULIN-RECEPTOR

Our previous study using a deletion mutant indicated that the COOH-ter minal (CT) domain of the insulin receptor plays important roles in bot h 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 d omain and examined its effect on insulin and IGF-I receptor protein ki nases. The purified CT domain stimulated the kinase activities of puri fied insulin receptor-transmembrane/cytoplasmic domain (IRTMTPK) and i ts CT domain-deletion mutant (IRTMTPK Delta CT), 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 autophosp horylation was examined, a marked increase in autophosphorylation was observed only with IRTMTPK Delta CT, These results suggest that the CT domain specifically interacts with the insulin receptor cytoplasmic d omain, thereby activating the kinase or autophosphorylation activity. (C) 1994 Academic Press, Inc.