Toward understanding the role of insulin alpha-helix II in the growth-promoting activity of insulin.
For further understanding the contribution of the alpha-helix II (alphaII) in the growth-promoting activity of insulin, the residues A2Ile, A5Gln, and A8Thr located in alphaII were mutated to Leu, Glu, and Tyr, respectively. Three mutant insulins, [A2Leu]human insulin, [A5Glu]human insulin, and [A8Tyr]human insulin, were prepared by means of site-directed mutagenesis. The in vitro growth-promoting activities of the three mutant insulins, measured using GR2H6 cells, were 7.5%, 291%, and 250% of that of native insulin, respectively. Their receptor-binding activities to the insulin receptor were 2.3%, 46.7%, and 138.7%, respectively, compared with native insulin. Both the growth-promoting and receptor-binding activities of [A2Leu]human insulin and [A3Leu]insulin (Shi et al., 1997) were parallel and greatly decreased compared with native insulin. The results demonstrate that the residues A2Ile and A3Val in the alphaII are essential for the growth-promoting activity of insulin, and the growth-promoting function of insulin might be performed through, or mainly through, binding to the insulin receptor. The growth-promoting activities of [A5Glu]human insulin and [A8Tyr]human insulin were increased 6-fold and 2-fold, respectively, compared with native insulin, indicating that their growth-promoting activities might be expressed by, or mainly by, binding to the IGF-1 receptor.
Chen
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State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, People's Republic of China.
Feng
Y M
YM
D020816:Amino Acid Motifs / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured; D002942:Circular Dichroism; D006801:Humans; D007328:Insulin / Q000737:chemistry / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary / Q000502:physiology; D011972:Receptor, Insulin / Q000737:chemistry / Q000502:physiology*; D013329:Structure-Activity Relationship; D014170:Transformation, Genetic / Q000502:physiology; D014407:Tumor Cells, Cultured
D007328:Insulin; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin