Structure of the insulin receptor ectodomain reveals a folded-over conformation

CSIRO Molecular & Health Technologies, 343 Royal Parade, Parkville, Victoria 3052, Australia.
Nature (Impact Factor: 41.46). 10/2006; 443(7108):218-21. DOI: 10.1038/nature05106
Source: PubMed


The insulin receptor is a phylogenetically ancient tyrosine kinase receptor found in organisms as primitive as cnidarians and insects. In higher organisms it is essential for glucose homeostasis, whereas the closely related insulin-like growth factor receptor (IGF-1R) is involved in normal growth and development. The insulin receptor is expressed in two isoforms, IR-A and IR-B; the former also functions as a high-affinity receptor for IGF-II and is implicated, along with IGF-1R, in malignant transformation. Here we present the crystal structure at 3.8 A resolution of the IR-A ectodomain dimer, complexed with four Fabs from the monoclonal antibodies 83-7 and 83-14 (ref. 4), grown in the presence of a fragment of an insulin mimetic peptide. The structure reveals the domain arrangement in the disulphide-linked ectodomain dimer, showing that the insulin receptor adopts a folded-over conformation that places the ligand-binding regions in juxtaposition. This arrangement is very different from previous models. It shows that the two L1 domains are on opposite sides of the dimer, too far apart to allow insulin to bind both L1 domains simultaneously as previously proposed. Instead, the structure implicates the carboxy-terminal surface of the first fibronectin type III domain as the second binding site involved in high-affinity binding.

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    • "1997; McKern et al. 2006). The severe biochemical and clinical consequences of this latter mutation highlights the crucial role of the cysteine residues in the INSR ligand-binding domain, not only in ligand binding, but also in stabilizing the three-dimensional IR structure affecting intracellular INSR processing. "
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    • "The attachment of Fabs resulted in a crystal packing arrangement that involved almost solely Fab-to-Fab interfaces, thus overcoming the hindrance to crystallization posed by the surface glycans of the IR ectodomain. These crystals were obtained by Meizhen Lou (McKern et al., 2006), who, remarkably, had also been a technician within the Beijing Insulin Structure Group working on the crystallization of insulin in the early 1970s! The three-dimensional structure revealed that the IR adopted a folded-over (inverted " V " ) conformation that placed putative ligand binding regions in close juxtaposition. "
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