N-terminal Deletion Mutants of Insulin-like Growth Factor-II (IGF-II) Show Thr and Leu Important for Binding to Insulin and IGF-I Receptors and Leu Critical for All IGF-II Functions

• Published in: The Journal of biological chemistry 1995-07, Vol.270 (30), p.18013
• Main Authors: Ryuji Hashimoto, Hiroyuki Fujiwara, Nobuyuki Higashihashi, Tomoko Enjoh-Kimura, Hiroaki Terasawa, Yoko Fujita-Yamaguchi, Fuyuhiko Inagaki, James F. Perdue, Katsu-ichi Sakano
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• 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 Gly 8 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 ≥50% levels of that of rIGF-II, the affinity of des-(1-7)-rIGF-II decreased to 10% and 3%, respectively, of that of rIGF-II. When the octapeptide including Leu 8 was removed prior to the Cys 9 -Cys intrachain bond, the relative affinity of this deletion mutant, des-(1-8)-rIGF-II, for these receptors dramatically decreased to