Involvement of phenylalanine 23 in the binding of IGF-1 to the insulin and type I IGF receptor.
The hydrophobic residue Phe-23 lies on a surface of insulin like growth factor 1 (IGF-1) which may be involved in binding to the type I IGF and insulin receptors. The possibility that Phe-23 participates directly in binding to these receptors has been investigated by comparing the properties of [F23G]IGF-1, a mutant of insulin-like growth factor 1 in which Phe-23 has been replaced by Gly, with those of IGF-1 and insulin. [F23G]IGF-1 has a 48-fold lower affinity for the type I IGF receptor, a markedly reduced affinity for the insulin receptor and a 100-fold reduced affinity for insulin-like growth factor binding proteins (IGFBPs) compared to IGF-1. [F23G]IGF-1 is a full IGF-1 agonist as measured by its ability to stimulate cell proliferation. Its potency was only 4.5-fold less than IGF-1, probably because its bioavailability was increased as a result of its reduced affinity for IGFBPs. The large reduction in the affinity of [F23G]IGF-1 for the type I IGF receptor and insulin receptor contrasts with the lack of effect of the corresponding alteration to insulin [FB24G]. Phe-B24 is not thought to be involved directly in the binding of insulin to the insulin receptor and the C-terminus of the B-chain of insulin is suggested to be displaced on binding. We suggest that for IGF-1, the C-terminus of the B chain cannot be displaced because of the presence of the C-domain and the large reduction in the binding affinities of [F23G]IGF-1 suggest that the Phe-23 side chain may be directly involved in binding of IGF-1 to the type I IGF and insulin receptors.
Hodgson
D R
DR
Department of Pathology, University of Newcastle Upon Tyne, Royal Victoria Infirmary, UK.
May
F E
FE
Westley
B R
BR
D001665:Binding Sites / Q000235:genetics; D002455:Cell Division / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D009154:Mutation; D010649:Phenylalanine; D011869:Radioligand Assay; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D007328:Insulin; D011994:Recombinant Proteins; D010649:Phenylalanine; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1