N-terminal deletion mutants of insulin-like growth factor-II (IGF-II) show Thr7 and Leu8 important for binding to insulin and IGF-I receptors and Leu8 critical for all IGF-II functions

• Published in: The Journal of biological chemistry Vol. 270; no. 30; pp. 18013 - 18018
• Main Authors: Hashimoto, R, Fujiwara, H, Higashihashi, N, Enjoh-Kimura, T, Terasawa, H, Fujita-Yamaguchi, Y, Inagaki, F, Perdue, J F, Sakano, K
• Format: Journal Article
• Language: English
• Published: United States 28.07.1995
• Subjects: 3T3 Cells; Amino Acid Sequence; Animals; Base Sequence; DNA; Humans; Insulin-Like Growth Factor II - genetics; Insulin-Like Growth Factor II - metabolism; Leucine - genetics; Leucine - metabolism; Mice; Mice, Inbred BALB C; Molecular Sequence Data; Mutagenesis, Site-Directed; Protein Binding; Receptor, IGF Type 1 - metabolism; Receptor, Insulin - metabolism; Sequence Deletion; Threonine - genetics; Threonine - metabolism
• ISSN: 0021-9258
• DOI: 10.1074/jbc.270.30.18013

To define the role of the N-terminal region of insulin-like growth factor-II (IGF-II) in its binding to insulin and IGF receptors, deletion mutants des-(1-5)-, des-(1-7)-, and des-(1-8)-recombinant (r) IGF-II, and the Gly8 for Leu substitution mutant of rIGF-II were prepared by site-directed mutagenesis, expressed in Escherichia coli, and purified. The binding affinity and mitogenic activity of these rIGF-II mutants as well as commercially available des-(1-6)-rIGF-II were analyzed. While the relative affinity of des-(1-5)- and des-(1-6)-rIGF-II for purified human insulin and IGF-I receptors remained at > or = 50% levels of that of rIGF-II, the affinity of des-(1-7)-rIGF-II decreased to approximately 10% and approximately 3%, respectively, of that of rIGF-II. When the octapeptide including Leu8 was removed prior to the Cys9-Cys47 intrachain bond, the relative affinity of this deletion mutant, des-(1-8)-rIGF-II, for these receptors dramatically decreased to < 1% of that of rIGF-II. Substituting Gly8 for Leu in rIGF-II decreased the affinity of this mutant for the IGF-I and insulin receptors to about the same extent. These results suggest that the side chains of Thr7 and Leu8 may play an important role in retaining all of the IGF-II functions. Decreases in the relative affinity for binding of the mutants to these receptors paralleled the decreases in their mitogenic potency for cultured Balb/c 3T3 cells. Although the relative affinity of des-(1-8)- or [Gly8]rIGF-II for rat IGF-II/CIM6-P (cation-independent mannose 6-phosphate) receptors was also < 1% of that of rIGF-II, the relative affinities of des-(1-5)-, des-(1-6)-, and des-(1-7)-rIGF-II for these receptors was significantly greater than that of rIGF-II. These results clearly demonstrate that Thr7 and Leu8 are important for binding to insulin and IGF-I receptors and Leu8 is critical for expression of all IGF-II functions.