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https://hdl.handle.net/2440/3037
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Type: | Journal article |
Title: | Role of N- and C-terminal residues of insulin-like growth factor (IGF)-binding protein-3 in regulating IGF complex formation and receptor activation |
Author: | Yan, X. Forbes, B. McNeil, K. Baxter, R. Firth, S. |
Citation: | Journal of Biological Chemistry, 2004; 279(51):53232-53240 |
Publisher: | Amer Soc Biochemistry Molecular Biology Inc |
Issue Date: | 2004 |
ISSN: | 0021-9258 1083-351X |
Statement of Responsibility: | Xiaolang Yan, Briony E. Forbes, Kerrie A. McNeil, Robert C. Baxter, and Sue M. Firth |
Abstract: | Insulin-like growth factor-binding protein-3 (IGFBP-3), the major IGFBP in the circulation, sequesters IGF in a stable ternary complex with the acid-labile subunit. The high affinity IGF-binding site is proposed to reside within an N-terminal hydrophobic domain in IGFBP-3, but C-terminal residues have also been implicated in the homologous protein IGFBP-5. We have mutated in various combinations Leu77, Leu80, and Leu81 in the N terminus and Gly217 and Gln223 in the C terminus of IGF-BP-3. All mutants retained immunoreactivity toward a polyclonal IGFBP-3 antibody, whereas IGF ligand blotting showed that all of the mutants had reduced binding to IGFs. Both solution IGF binding assays and BIAcore analysis indicated that mutations to the N-terminal region caused greater reduction in IGF binding activity than C-terminal mutations. The combined N- and C-terminal mutants showed undetectable binding to IGF-I but retained <10% IGF-II binding activity. Reduced ternary complex formation was seen only in mutants that had considerably reduced IGF-I binding, consistent with previous studies indicating that the binary IGF·IGFBP-3 complex is required for acid-labile subunit binding. Decreased IGF binding was also reflected in the inability of the mutants to inhibit IGF-I signaling in IGF receptor overexpressing cells. However, when present in excess, IGFBP-3 analogs defined as non-IGF-binding by biochemical assays could still inhibit IGF signaling. This suggests that residual binding activity of IGFBP-3 mutants may still be sufficient to inhibit IGF biological activity and questions the use of such analogs to study IGF-independent effects of IGFBP-3. |
Keywords: | Cells, Cultured NIH 3T3 Cells Animals Mice Insulin Glutamine Leucine Glycine Insulin-Like Growth Factor Binding Protein 3 Insulin-Like Growth Factor Binding Protein 5 Recombinant Proteins DNA Primers Ligands Biological Assay Signal Transduction Amino Acid Sequence Protein Structure, Tertiary Protein Binding Sequence Homology, Amino Acid Phosphorylation Dose-Response Relationship, Drug Kinetics Mutation Plasmids Time Factors Molecular Sequence Data |
DOI: | 10.1074/jbc.M409345200 |
Published version: | http://dx.doi.org/10.1074/jbc.m409345200 |
Appears in Collections: | Aurora harvest 6 Molecular and Biomedical Science publications |
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