How IGF-II Binds to the Human Type 1 Insulin-like Growth Factor Receptor

Human type 1 insulin-like growth factor receptor (IGF-1R) signals chiefly in response to the binding of insulin-like growth factor I. Relatively little is known about the role of insulin-like growth factor II signaling via IGF-1R, despite the affinity of insulin-like growth factor II for IGF-1R being within an order of magnitude of that of insulin-like growth factor I. Here, we describe the cryoelectron microscopy structure of insulin-like growth factor II bound to a leucine-zipper-stabilized IGF-1R ectodomain, determined in two conformations to a maximum average resolution of 3.2 Å. The two conformations differ in the relative separation of their respective points of membrane entry, and comparison with the structure of insulin-like growth factor I bound to IGF-1R reveals long-suspected differences in the way in which the critical C domain of the respective growth factors interact with IGF-1R. [Display omitted] •Cryo-EM structure of IGF-II bound to leucine-zippered human IGF-1R ectodomain•IGF-II C domain interacts with receptor differently to that of IGF-I Insulin-like growth factors I and II differ in the length of their C domain, the segment that links growth factor B and A domains. Xu et al. show that the different 3D modes of C-domain engagement with type 1 insulin-like growth factor receptor align with their receptor affinity.