title: Structural and functional characteristics of the Val44Met insulin-like growth factor I missense mutation: correlation with effects on growth and development.
abstract: We have previously described the phenotype resulting from a missense mutation in the IGF-I gene, which leads to expression of IGF-I with a methionine instead of a valine at position 44 (Val44Met IGF-I). This mutation caused severe growth and mental retardation as well as deafness evident at birth and growth retardation in childhood, but is relatively well tolerated in adulthood. We have conducted a biochemical and structural analysis of Val44Met IGF-I to provide a molecular basis for the phenotype observed. Val44Met IGF-I exhibits a 90-fold decrease in type 1 IGF receptor (IGF-1R) binding compared with wild-type human IGF-I and only poorly stimulates autophosphorylation of the IGF-1R. The ability of Val44Met IGF-I to signal via the extracellular signal-regulated kinase 1/2 and Akt/protein kinase B pathways and to stimulate DNA synthesis is correspondingly poorer. Binding or activation of both insulin receptor isoforms is not detectable even at micromolar concentrations. However, Val44Met IGF-I binds IGF-binding protein-2 (IGFBP-2), IGFBP-3, and IGFBP-6 with equal affinity to IGF-I, suggesting the maintenance of overall structure, particularly in the IGFBP binding domain. Structural analysis by nuclear magnetic resonance confirms retention of near-native structure with only local side-chain disruptions despite the significant loss of function. To our knowledge, our results provide the first structural study of a naturally occurring mutant human IGF-I associated with growth and developmental abnormalities and identifies Val44 as an essential residue involved in the IGF-IGF-1R interaction.
authors.affiliation: School of Molecular and Biomedical Science, University of Adelaide, Adelaide, 5005 South Australia.
authors.forename: Adam
authors.initials: A
authors.lastname: Denley
authors.forename: Chunxiao C
authors.initials: CC
authors.lastname: Wang
authors.forename: Kerrie A
authors.initials: KA
authors.lastname: McNeil
authors.forename: Marie J E
authors.initials: MJ
authors.lastname: Walenkamp
authors.forename: Hermine
authors.initials: H
authors.lastname: van Duyvenvoorde
authors.forename: Jan M
authors.initials: JM
authors.lastname: Wit
authors.forename: John C
authors.initials: JC
authors.lastname: Wallace
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Norton
authors.forename: Marcel
authors.initials: M
authors.lastname: Karperien
authors.forename: Briony E
authors.initials: BE
authors.lastname: Forbes
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D001681:Biological Assay; D015153:Blotting, Western; D049109:Cell Proliferation; D004247:DNA / Q000378:metabolism; D004252:DNA Mutational Analysis; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D020128:Inhibitory Concentration 50; D007328:Insulin / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000235:genetics* / Q000378:metabolism; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008715:Methionine / Q000737:chemistry*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D020125:Mutation, Missense; D010641:Phenotype; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D015398:Signal Transduction; D020349:Surface Plasmon Resonance; D013936:Thymidine / Q000737:chemistry; D013997:Time Factors; D014633:Valine / Q000737:chemistry*
chemical_list: D007328:Insulin; D008024:Ligands; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D004247:DNA; D008715:Methionine; D017526:Receptor, IGF Type 1; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D014633:Valine; D013936:Thymidine