PMID: 29512653

Authors:

Scapin G, Dandey VP, Zhang Z, Prosise W, Hruza A, Kelly T, Mayhood T, Strickland C, Potter CS, Carragher B

Title:

Structure of the Insulin Receptor-Insulin Complex by Single Particle CryoEM analysis.

Journal:

Nature. 2018 Feb 28. pii: nature26153. doi: 10.1038/nature26153.

Abstract:

The insulin receptor (IR) is a dimeric protein that plays a crucial role in controlling glucose homeostasis, regulating lipid, protein and carbohydrate metabolism, and modulating brain neurotransmitter levels(1,2). IR dysfunction has been associated with many diseases, including diabetes, cancer, and Alzheimer's disease(1,2,4). The primary sequence has been known since the 1980s(5), and is composed of an extracellular portion (ectodomain, ECD), a single transmembrane helix and an intracellular tyrosine kinase domain. Insulin binding to the dimeric ECD triggers kinase domain auto-phosphorylation and subsequent activation of downstream signaling molecules. Biochemical and mutagenesis data have identified two putative insulin binding sites (S1 and S2)(6). While insulin bound to an ECD fragment containing S1 and the apo ectodomain have been characterized structurally(7,8), details of insulin binding to the full receptor and the signal propagation mechanism are still not understood. Here we report single particle cryoEM reconstructions for the 1:2 (4.3 A) and 1:1 (7.4 A) IR ECD dimer:Insulin complexes. The symmetric 4.3 A structure shows two insulin molecules per dimer, each bound between the Leucine-rich sub domain L1 of one monomer and the first fibronectin-like domain (FnIII-1) of the other monomer, and making extensive interactions with the alpha subunit C-terminal helix (alpha-CT helix). The 7.4 A structure has only one similarly bound insulin per receptor dimer. The structures confirm the S1 binding interactions and define the full S2 binding site. These insulin receptor states suggest that recruitment of the alpha-CT helix upon binding of the first insulin changes the relative subdomain orientations and triggers downstream signal propagation.