The C Region of Human Insulin-like Growth Factor (IGF) I Is Required for High Affinity Binding to the Type 1 IGF Receptor

M L Bayne,J Applebaum,D Underwood,G G Chicchi,B G Green,N S Hayes,M A Cascieri

doi:10.1016/s0021-9258(18)60418-1

Abstract

We have produced and characterized the binding properties of three structural analogs of human insulin-like growth factor I (hIGF-I). These analogs are [1-62]hIGF-I, an analog lacking the carboxyl-terminal 8-amino acid D region of hIGF-I; [1-27, Gly4, 38-70]hIGF-I, an analog in which residues 28-37 of the C region of hIGF-I are replaced by a 4-reside glycine bridge; and [1-27,Gly4,38-62]hIGF-I, an analog with the C region glycine replacement and a D region deletion. The removal of the D region of hIGF-I has little effect on binding to the type 1 and type 2 insulin-like growth factor (IGF) receptors. [1-62]hIGF-I has 2-fold higher affinity for the insulin receptor and 4-fold higher affinity for IGF serum-binding proteins. The replacement of the C region of hIGF-I with a four-glycine span results in a 30-fold loss of affinity for the type 1 IGF receptor. However this analog has near normal affinity for the type 2 IGF receptor, the insulin receptor, and IGF serum-binding proteins. Incorporating the C region glycine replacement and the D region deletion into one analog does not affect binding to either the type 2 receptor or to IGF serum-binding proteins. As predicted from the single deletion analogs [1-27,Gly4,38-62]hIGF-I has reduced affinity for the type 1 IGF receptor (approximately 40-fold) and increased affinity for the insulin receptor (5-fold). These data indicate that determinants in the C region of hIGF-I are involved in maintaining high affinity binding to the type 1 IGF receptor and that neither the C region nor the D region are required for high affinity binding to the type 2 IGF receptor or to IGF serum-binding proteins.

Highlights

We have produced and characterizedthebinding from the type 1IGF receptor and has no measurable affinity properties of three structuralanalogs of human insu- for insulin (3, 5 ) . hIGF-Ibinds with high affinity to two lin-like growth factor I
Human insulin-like growthfactor (IGF)-I shows a high degree of sequence homology with porcine and human insulin [1].Aligning residues 1-29 of hIGF-I with residues B2-B30 of insulin indicates that 45% of the residues are conserved
Design and Construction of Mutant hZGF-Z Genes-In order to examine the role of the D region of hIGF-I, the 3’ end of a synthetic gene for human IGF-I [16] was modified to encode [l-62lhIGF-I by replacing the 51-base pair XhoI/BamHI fragment from pJY2 [17] with a 24-base pair synthetic fragment encoding amino acids 57-62 followed bya stopcodon

Summary

Introduction

We have produced and characterizedthebinding from the type 1IGF receptor and has no measurable affinity properties of three structuralanalogs of human insu- for insulin (3, 5 ) . hIGF-Ibinds with high affinity to two lin-like growth factor I (hIGF-I). Replacement of the C region of hIGF-I with a four- I shows a high degreeof sequence homology (52%)when glycine span results ina 30-fold loss of affinity for the the amino acids 42-62 are aligned with the A chain of insulin type 1 IGF receptor.

Results

Conclusion