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- Title
Structure of the IGF-binding domain of the insulin-like growth factor-binding protein-5 (IGFBP-5): implications for IGF and IGF-I receptor interactions.
- Authors
Kalus, W; Zweckstetter, M; Renner, C; Sanchez, Y; Georgescu, J; Grol, M; Demuth, D; Schumacher, R; Dony, C; Lang, K; Holak, T A
- Abstract
Binding proteins for insulin-like growth factors (IGFs) IGF-I and IGF-II, known as IGFBPs, control the distribution, function and activity of IGFs in various cell tissues and body fluids. Insulin-like growth factor-binding protein-5 (IGFBP-5) is known to modulate the stimulatory effects of IGFs and is the major IGF-binding protein in bone tissue. We have expressed two N-terminal fragments of IGFBP-5 in Escherichia coli; the first encodes the N-terminal domain of the protein (residues 1-104) and the second, mini-IGFBP-5, comprises residues Ala40 to Ile92. We show that the entire IGFBP-5 protein contains only one high-affinity binding site for IGFs, located in mini-IGFBP-5. The solution structure of mini-IGFBP-5, determined by nuclear magnetic resonance spectroscopy, discloses a rigid, globular structure that consists of a centrally located three-stranded anti-parallel beta-sheet. Its scaffold is stabilized further by two inside packed disulfide bridges. The binding to IGFs, which is in the nanomolar range, involves conserved Leu and Val residues localized in a hydrophobic patch on the surface of the IGFBP-5 protein. Remarkably, the IGF-I receptor binding assays of IGFBP-5 showed that IGFBP-5 inhibits the binding of IGFs to the IGF-I receptor, resulting in reduction of receptor stimulation and autophosphorylation. Compared with the full-length IGFBP-5, the smaller N-terminal fragments were less efficient inhibitors of the IGF-I receptor binding of IGFs.
- Publication
The EMBO journal, 1998, Vol 17, Issue 22, p6558
- ISSN
0261-4189
- Publication type
Journal Article
- DOI
10.1093/emboj/17.22.6558