Solution structure of human insulin-like growth factor II; recognition sites for receptors and binding proteins

The three-dimensional structure of human insulin-like growth factor II was determined at high resolution in aqueous solution by NMR and simulated annealing based calculations. The structure is quite similar to those of insulin and insulin-like growth factor I, which consists of an alpha-helix followed by a turn and a strand in the B-region and two antiparallel alpha-helices in the A-region. However, the regions of Ala1-Glu6, Pro31-Arg40 and Thr62-Glu67 are not well-defined for lack of distance constraints, possibly due to motional flexibility. Based on the resultant structure and the results of structure-activity relationships, we propose the interaction sites of insulin-like growth factor II with the type 2 insulin-like growth factor receptor and the insulin-like growth factor binding proteins. These sites partially overlap with each other at the opposite side of the putative binding surface to the insulin receptor and the type 1 insulin-like growth factor receptor. We also discuss the interaction modes of insulin-like growth factor II with the insulin receptor and the type 1 insulin-like growth factor receptor.