Binding of mutants of human insulin-like growth factor II to insulin-like growth factor binding proteins 1-6.
A family of six specific insulin-like growth factor binding proteins (IGFBPs) modulates the biological actions of the insulin-like growth factors, IGF-I and IGF-II. In the present study, we determined the binding affinity of purified human IGFBPs 1-6 for recombinant human IGF-II mutants whose binding to IGF-I, IGF-II/mannose 6-phosphate, and insulin ... receptors was previously reported (Sakano, K., Enjoh, T., Numata, F., Fujiwara, H., Marumoto, Y., Higashihashi, N., Sato, Y., Perdue, J. F., and Fujita-Yamaguchi, Y. (1991) J. Biol. Chem. 266, 20626-20635). Of the regions studied, the most important determinants of IGF-II binding to the IGFBPs were A-domain residues 48-50 and B-domain residue 26. Substitution of residues 48-50 with the analogous residues from human insulin (Thr-Ser-Ile) reduced binding to IGFBP-1, -5, and -6 more than 50-fold and to IGFBP-4 by 15-50-fold; binding to IGFBP-2 and -3 was reduced 6-12-fold. The same substitution markedly reduced binding to the IGF-II/mannose 6-phosphate receptor but not to IGF-I or insulin receptors. Although substitution of residues 54 and 55 with the analogous residues from IGF-I (Arg-Arg) abolished binding to the IGF-II/mannose 6-phosphate receptor, binding to IGFBPs was not substantially affected. Substitution of Phe26 with Ser or Leu, which decreased binding to the IGF-I and insulin receptors, reduced binding to IGFBP-1 and -6 up to 80-fold, but had lesser effects on the other IGFBPs. [Leu27]IGF-II and [Leu43]IGF-II, which had a more markedly reduced affinity for the IGF-I and insulin receptors than did [Ser26]IGF-II, were bound by the IGFBPs with relatively unchanged affinity compared with IGF-II. Thus, the determinants of IGF-II binding to IGFBPs partially overlap those for the IGF-II/mannose 6-phosphate receptor and overlap those for the IGF-I receptor to a lesser extent. IGFBP-1 and IGFBP-6 are most sensitive to changes in IGF-II structure, although IGFBP-1 binds IGF-I and IGF-II with equal affinity, whereas IGFBP-6 has a marked preferential binding affinity for IGF-II. IGF-II mutants with selective impairment in recognition by specific IGFBPs or receptors will provide a useful tool for dissecting the role of the different IGF binding macromolecules in the mediation of IGF-II actions.
Mesh Terms:
Amino Acid Sequence, Amniotic Fluid, Animals, Binding, Competitive, Carrier Proteins, Female, Humans, Insulin-Like Growth Factor Binding Protein 1, Insulin-Like Growth Factor Binding Protein 2, Insulin-Like Growth Factor Binding Protein 4, Insulin-Like Growth Factor Binding Protein 5, Insulin-Like Growth Factor Binding Protein 6, Insulin-Like Growth Factor Binding Proteins, Insulin-Like Growth Factor I, Insulin-Like Growth Factor II, Kinetics, Liver, Molecular Sequence Data, Mutagenesis, Site-Directed, Pregnancy, Rats, Recombinant Proteins, Sequence Deletion, Sequence Homology, Amino Acid
Amino Acid Sequence, Amniotic Fluid, Animals, Binding, Competitive, Carrier Proteins, Female, Humans, Insulin-Like Growth Factor Binding Protein 1, Insulin-Like Growth Factor Binding Protein 2, Insulin-Like Growth Factor Binding Protein 4, Insulin-Like Growth Factor Binding Protein 5, Insulin-Like Growth Factor Binding Protein 6, Insulin-Like Growth Factor Binding Proteins, Insulin-Like Growth Factor I, Insulin-Like Growth Factor II, Kinetics, Liver, Molecular Sequence Data, Mutagenesis, Site-Directed, Pregnancy, Rats, Recombinant Proteins, Sequence Deletion, Sequence Homology, Amino Acid
J. Biol. Chem.
Date: May. 05, 1993
PubMed ID: 7683646
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