Binding site for the C‐domain of insulin‐like growth factor (IGF) binding protein‐6 on IGF‐II; implications for inhibition of IGF actions

Abstract
Insulin‐like growth factors (IGFs) are important mediators of growth and IGF‐binding proteins (IGFBPs) 1–6 regulate IGF actions. As IGFBP C‐terminal domains contribute to high‐affinity IGF binding, we have defined the binding site for the C‐domain of IGFBP‐6 on IGF‐II using NMR. This site lies adjacent to and between the binding sites for the IGFBP N‐domain and IGF‐I receptor (IGFIR), which have previously been found on opposite sides of the IGF molecule. The C‐domain is therefore likely to interfere with IGF binding to the IGFIR, providing a structural basis for the potent inhibitory effects of intact IGFBPs on IGF actions.