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Mol Endocrinol. 1991 Jul;5(7):987-94.

Mutations in the C-terminal part of insulin-like growth factor (IGF)-binding protein-1 result in dimer formation and loss of IGF binding capacity.

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Department of Pediatrics, Erasmus University/Sophia Childrens Hospital, Rotterdam, The Netherlands.


In an attempt to define domains in insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) that are involved in IGF binding, we subjected the carboxyl end of the coding region of IGFBP-1 cDNA to mutagenesis. Mutant cDNAs were isolated, characterized by sequencing, and cloned in an expression vector under control of the simian virus-40 (SV40) early promoter. The constructs were transfected into COS-1 cells, and the mutant proteins, secreted into the culture medium, were analyzed for IGF binding by ligand blotting. The results obtained show that deletion of the C-terminal 20 amino acids or introduction of frame-shifts in this region resulted in loss of IGF binding and for some mutants in the formation of dimeric IGFBP-1 molecules. These dimers are probably formed when cysteine-226 (Cys-226) is missing, and its putative partner is able to form intermolecular disulfide bonds. Site-directed mutagenesis demonstrated that most of the introduced point mutations in the C-terminal region did not affect IGF binding. Only mutation of Cys-226 to tyrosine completely abolished IGF binding, as did the introduction of a negatively charged amino acid in the vicinity of this residue. Again, dimers were observed, supporting that Cys-226 is essential for the conformation of IGFBP-1. In addition, our data suggest that an IGF-binding domain may be located in the vicinity of the intramolecular disulfide bond formed by Cys-226 and its putative partner.

[Indexed for MEDLINE]

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