Replacements of leucine 87 in human insulin receptor alter affinity for insulin

Insulin receptor-insulin interaction kinetics using multiplex surface plasmon resonance

Type 2 diabetes affects millions of people worldwide, and measuring the kinetics of insulin receptor-insulin interactions is critical to improving our understanding of this disease. In this paper, we describe, for the first time, a rapid, real-time, multiplex surface plasmon resonance (SPR) assay for studying the interaction between insulin and the insulin receptor ectodomain, isoform A (eIR-A). We used a scaffold approach in which anti-insulin receptor monoclonal antibody 83-7 (Abcam, Cambridge, UK) was first immobilized on the SPR sensorchip by amine coupling, followed by eIR-A capture. The multiplex SPR system (ProteOn XPR36™, Bio-Rad Laboratories, Hercules, CA) enabled measurement of replicate interactions with a single, parallel set of analyte injections, whereas repeated regeneration of the scaffold between measurements caused variable loss of antibody activity. Interactions between recombinant human insulin followed a two-site binding pattern, consistent with the literature, with a high-affinity site (dissociation constant K(D1)  = 38.1 ± 0.9 nM) and a low-affinity site (K(D2)  = 166.3 ± 7.3 nM). The predominantly monomeric insulin analogue Lispro had corresponding dissociation constants K(D1)  = 73.2 ± 1.8 nM and K(D2)  = 148.9 ± 6.1 nM, but the fit to kinetic data was improved when we included a conformational change factor in which the high-affinity site was converted to the low-affinity site. The new SPR assay enables insulin-eIR-A interactions to be followed in real time and could potentially be extended to study the effects of humoral factors on the interaction, without the need for insulin labeling.

Structural determinants of the insulin receptor-related receptor activation by alkali

IRR is a member of the insulin receptor (IR) family that does not have any known agonist of a peptide nature but can be activated by mildly alkaline medium and was thus proposed to function as an extracellular pH sensor. IRR activation by alkali is defined by its N-terminal extracellular region. To reveal key structural elements involved in alkali sensing, we developed an in vitro method to quantify activity of IRR and its mutants. Replacing the IRR L1C domains (residues 1-333) or L2 domain (residues 334-462) or both with the homologous fragments of IR reduced the receptor activity to 35, 64, and 7% percent, respectively. Within L1C domains, five amino acid residues (Leu-135, Gly-188, Arg-244, and vicinal His-318 and Lys-319) were identified as IRR-specific by species conservation analysis of the IR family. These residues are exposed and located in junctions between secondary structure folds. The quintuple mutation of these residues to alanine had the same negative effect as the entire L1C domain replacement, whereas none of the single mutations was as effective. Separate mutations of these five residues and of L2 produced partial negative effects that were additive. The pH dependence of cell-expressed mutants (L1C and L2 swap, L2 plus triple LGR mutation, and L2 plus quintuple LGRHK mutation) was shifted toward alkalinity and, in contrast with IRR, did not show significant positive cooperativity. Our data suggest that IRR activation is not based on a single residue deprotonation in the IRR ectodomain but rather involves synergistic conformational changes at multiple points.

Development of endometrial carcinoma in a patient with leprechaunism (donohue syndrome)

Leprechaunism is a rare autosomal recessive disease that is characterized by severe insulin resistance. This disease is caused by a defective insulin receptor and features abnormal glucose metabolism and retarded intrauterine and postnatal growth. However, there are few reports on the long-term course of leprechaunism. We reported the long-term clinical course and rh-IGF-1 treatment in a patient with leprechaunism. During follow-up her diabetes gradually deteriorated despite of treatment of rh-IGF-1. Furthermore, she developed endometrioid adenocarcinoma at the age of 24 yr. The development of endometrial disease must be carefully followed up in this disease.

Development of Endometrial Carcinoma in a Patient with Leprechaunism (Donohue Syndrome)

Leprechaunism is a rare autosomal recessive disease that is characterized by severe insulin resistance. This disease is caused by a defective insulin receptor and features abnormal glucose metabolism and retarded intrauterine and postnatal growth. However, there are few reports on the long-term course of leprechaunism. We reported the long-term clinical course and rh-IGF-1 treatment in a patient with leprechaunism. During follow-up her diabetes gradually deteriorated despite of treatment of rh-IGF-1. Furthermore, she developed endometrioid adenocarcinoma at the age of 24 yr. The development of endometrial disease must be carefully followed up in this disease.

A comparative structural bioinformatics analysis of the insulin receptor family ectodomain based on phylogenetic information

The insulin receptor (IR), the insulin-like growth factor 1 receptor (IGF1R) and the insulin receptor-related receptor (IRR) are covalently-linked homodimers made up of several structural domains. The molecular mechanism of ligand binding to the ectodomain of these receptors and the resulting activation of their tyrosine kinase domain is still not well understood. We have carried out an amino acid residue conservation analysis in order to reconstruct the phylogeny of the IR Family. We have confirmed the location of ligand binding site 1 of the IGF1R and IR. Importantly, we have also predicted the likely location of the insulin binding site 2 on the surface of the fibronectin type III domains of the IR. An evolutionary conserved surface on the second leucine-rich domain that may interact with the ligand could not be detected. We suggest a possible mechanical trigger of the activation of the IR that involves a slight 'twist' rotation of the last two fibronectin type III domains in order to face the likely location of insulin. Finally, a strong selective pressure was found amongst the IRR orthologous sequences, suggesting that this orphan receptor has a yet unknown physiological role which may be conserved from amphibians to mammals.

The first three domains of the insulin receptor differ structurally from the insulin-like growth factor 1 receptor in the regions governing ligand specificity

The insulin receptor (IR) and the type-1 insulin-like growth factor receptor (IGF1R) are homologous multidomain proteins that bind insulin and IGF with differing specificity. Here we report the crystal structure of the first three domains (L1-CR-L2) of human IR at 2.3 A resolution and compare it with the previously determined structure of the corresponding fragment of IGF1R. The most important differences seen between the two receptors are in the two regions governing ligand specificity. The first is at the corner of the ligand-binding surface of the L1 domain, where the side chain of F39 in IR forms part of the ligand binding surface involving the second (central) beta-sheet. This is very different to the location of its counterpart in IGF1R, S35, which is not involved in ligand binding. The second major difference is in the sixth module of the CR domain, where IR contains a larger loop that protrudes further into the ligand-binding pocket. This module, which governs IGF1-binding specificity, shows negligible sequence identity, significantly more alpha-helix, an additional disulfide bond, and opposite electrostatic potential compared to that of the IGF1R.

Structural biology of insulin and IGF1 receptors: implications for drug design

Type 2 diabetes mellitus -- in which the body produces insufficient amounts of insulin or the insulin that is produced does not function properly to control blood glucose -- is an increasingly common disorder. Prospective clinical studies have proven the benefits of tighter glucose control in reducing the frequency and severity of complications of the disease, leading to the advocation of earlier and more aggressive use of insulin therapy. Given the reluctance of patients with type 2 diabetes to inject themselves with insulin, orally active insulin mimetics would be a major therapeutic advance. Here, we discuss recent progress in understanding the structure-function relationships of the insulin and insulin-like growth factor 1 (IGF1) receptors, their mechanism of activation and their implications for the design of insulin-receptor agonists for diabetes therapy and IGF1-receptor antagonists for cancer therapy.

Hydrochlorothiazide effectively reduces urinary calcium excretion in two Japanese patients with gain-of-function mutations of the calcium-sensing receptor gene

Gain-of-function mutations of the calcium-sensing receptor (CaR) gene cause autosomal dominant and/or sporadic hypocalcemia with hypercalciuria. Because treatment of the hypocalcemia with vitamin D and/or calcium in patients with such mutations results in increased hypercalciuria, nephrocalcinosis, and renal impairment, its use should be limited to alleviating the symptoms of symptomatic patients. Because thiazide diuretics have been successfully used to treat patients with hypercalciuria and hypoparathyroidism, they are theoretically useful in reducing urine calcium excretion and maintaining serum calcium levels in patients with gain-of-function mutations of the CaR gene. In this study, we report on the clinical course, molecular analysis, and effects of hydrochlorothiazide therapy in two Japanese patients with gain-of-function mutations of the CaR gene. Within a few weeks after birth, they developed generalized tonic seizures due to hypocalcemia (serum calcium values: 1.1 mmol/liter and 1.3 mmol/liter, respectively). Despite treatment with the standard dose of 1,25-dihydroxyvitamin D(3) in one patient and 1alpha-hydroxyvitamin D(3) in the other, acceptable serum calcium levels near the lower limit of normal were not established, and their urinary calcium excretion inappropriately increased. Addition of hydrochlorothiazide (1 mg/kg) reduced their urinary calcium excretion and maintained their serum calcium concentrations near the lower limit of normal, allowing the 1,25-dihydroxyvitamin D(3) and 1alpha-hydroxyvitamin D(3) doses to be reduced, and it alleviated their symptoms. A heterozygous missense mutation was identified in both patients. In one patient, the mutation was A843E in the seventh transmembrane domain of the CaR, and in the other it was L125P in the N-terminal extracellular domain. In vitro transient transfection of their mutant CaR cDNAs into HEK293 cells shifted the concentration-response curve of Ca(2+) to the left. In conclusion, two sporadic cases of hypercalciuric hypocalcemia were due to de novo gain-of-function mutations of the CaR gene. Hydrochlorothiazide with vitamin D(3) successfully reduced the patients' urinary calcium excretion and controlled their serum calcium concentrations and symptoms. Thiazide diuretics are effective in patients with gain-of function mutations of the CaR gene.

Distinct and overlapping functions of insulin and IGF-I receptors

Targeted gene mutations have established distinct, yet overlapping, developmental roles for receptors of the insulin/IGF family. IGF-I receptor mediates IGF-I and IGF-II action on prenatal growth and IGF-I action on postnatal growth. Insulin receptor mediates prenatal growth in response to IGF-II and postnatal metabolism in response to insulin. In rodents, unlike humans, insulin does not participate in embryonic growth until late gestation. The ability of the insulin receptor to act as a bona fide IGF-II-dependent growth promoter is underscored by its rescue of double knockout Igf1r/Igf2r mice. Thus, IGF-II is a true bifunctional ligand that is able to stimulate both insulin and IGF-I receptor signaling, although with different potencies. In contrast, the IGF-II/cation-independent mannose-6-phosphate receptor regulates IGF-II clearance. The growth retardation of mice lacking IGF-I and/or insulin receptors is due to reduced cell number, resulting from decreased proliferation. Evidence from genetically engineered mice does not support the view that insulin and IGF receptors promote cellular differentiation in vivo or that they are required for early embryonic development. The phenotypes of insulin receptor gene mutations in humans and in mice indicate important differences between the developmental roles of insulin and its receptor in the two species.

Identification of a heregulin binding site in HER3 extracellular domain

HER3 (also known as c-Erb-b3) is a type I receptor tyrosine kinase similar in sequence to the epidermal growth factor (EGF) receptor. The extracellular segment of this transmembrane receptor contains four domains. Domains I and II are similar in sequence to domains III and IV, respectively, and domains II and IV are cysteine-rich. We show that the EGF-like domain of heregulin (hrg) binds to domains I and II of HER3, in contrast to the EGF receptor, for which prior studies have shown that a construct consisting of domains III and portions of domain IV binds EGF. Next, we identified a putative hrg binding site by limited proteolysis of the recombinant extracellular domains of HER3 (HER3-ECD(I-IV)) in both the presence and absence of hrg. In the absence of hrg, HER3-ECD(I-IV) is cleaved after position Tyr(50), near the beginning of domain I. Binding of hrg to HER3-ECD(I-IV) fully protects position Tyr(50) from proteolysis. To confirm that domain I contains a hrg binding site, we expressed domains I and II (HER3-ECD(I-II)) and find that it binds hrg with 68 nm affinity. These data suggest that domains I and II of HER3-ECD(I-IV) act as a functional unit in folding and binding of hrg. Thus, our biochemical findings reinforce the structural hypothesis of others that HER3-ECD(I-IV) is similar to the insulin-like growth factor-1 receptor (IGF-1R), as follows: 1) The protected cleavage site in HER3-ECD(I-IV) corresponds to a binding footprint in domain I of IGF-1R; 2) HER3-ECD(I-II) binds hrg with a 68 nm dissociation constant, supporting the hypothesis that domain I is involved in ligand binding; and 3) the large accessible surface area (1749 A) of domain L1 of IGF-1R that is buried by domain S1, as well as the presence of conserved contacts in this interface of type 1 RTKs, suggests that domains L1 and S1 of IGF-1R function as a unit as observed for HER3-ECD(I-II). Our results are consistent with the proposal that HER3 has a structure similar to IGF-1R and binds ligand at a site in corresponding domains.

Congenital insulin resistance associated with a conformational alteration in a conserved beta-sheet in the insulin receptor L1 domain

The hormone binding site of members of the insulin receptor family is contained within a highly conserved extracellular region of the receptor. Recent crystallization of the N-terminal region of the binding site revealed two large domains (L1, L2), each organized as a single-stranded right-handed beta-helix, connected by a rod-shaped cysteine-rich domain. Here, we analyze two new naturally occurring mutations in a single beta-sheet within L1, D59G and L62P, that we previously identified in a young woman with classic congenital insulin resistance (type A). Substitution of D59G, a beta-sheet connecting loop residue, caused decreased hormone binding but did not disrupt overall folding, assembly, or movement to the cell surface. In contrast, replacement of the adjacent residue L62P, which is located within the beta-sheet, and positioned in a hormone binding surface, completely disrupted intracellular folding, oligomerization, and trafficking and resulted in aberrant proteolytic degradation. Immunohistochemistry in combination with biosynthetic studies showed that misfolded receptors were retained in an incorrect cellular location and that they colocalized with the resident endoplasmic reticulum chaperone calnexin. This study, together with other mutagenesis data, shows that formation of beta-sheet elements within the L1 beta-helix are critical for the folding of the entire extracellular domain of the receptor and that the hormone contact site is composed in part by residues in this domain.

Crystal structure of the first three domains of the type-1 insulin-like growth factor receptor

The type-1 insulin-like growth-factor receptor (IGF-1R) and insulin receptor (IR) are closely related members of the tyrosine-kinase receptor superfamily. IR is essential for glucose homeostasis, whereas IGF-1R is involved in both normal growth and development and malignant transformation. Homologues of these receptors are found in animals as simple as cnidarians. The epidermal growth-factor receptor (EGFR) family is closely related to the IR family and has significant sequence identity to the extracellular portion we describe here. We now present the structure of the first three domains of IGF-IR (L1-Cys-rich-L2) determined to 2.6 A resolution. The L domains each consist of a single-stranded right-handed beta-helix. The Cys-rich region is composed of eight disulphide-bonded modules, seven of which form a rod-shaped domain with modules associated in an unusual manner. The three domains surround a central space of sufficient size to accommodate a ligand molecule. Although the fragment (residues 1-462) does not bind ligand, many of the determinants responsible for hormone binding and ligand specificity map to this central site. This structure therefore shows how the IR subfamily might interact with their ligands.

Role of arginine 86 of the insulin receptor in insulin binding and activation of glucose transport

Mutations in the insulin receptor gene cause the inherited insulin resistant syndrome leprechaunism. Patient Atl-1 with leprechaunism was homozygous for the substitution of Arg-86 with Pro (R86P) in the alpha subunit of the insulin receptor. Fibroblasts homozygous for the mutant receptor had defective insulin binding, but increased glucose transport and receptor kinase activity. The R86P mutation is located in a putative beta turn N-terminal to a proposed insulin binding domain of the receptor [P. DeMeyts, J.L. Gu, R.M. Shymko, B.E. Kaplan, G.I. Bell, J. Whittaker, Mol. Endocrinol. 4 (1990) 409-416]. To get further insight into the mechanism of the paradoxical activation of receptor signalling by the R86P mutation, the codons for proline, alanine, and glycine were substituted in the R86 position of the insulin receptor cDNA by PCR-mediated mutagenesis and stably transfected into Chinese hamster ovary (CHO) cells. Insulin binding increased 10-20 fold in CHO cells transfected with the wild type, the R86A, and the R86G insulin receptor cDNA, but did not increase in cells expressing the R86P mutation. The R86P mutation caused a constitutive activation of insulin receptor phosphorylation in CHO cells, but did not increase basal glucose transport or its sensitivity to insulin stimulation. By contrast, transfection with the wild type and the R86A receptors increased 20-30 fold the sensitivity of glucose transport to stimulation by insulin. The R86G insulin receptor bound insulin normally, but was four times less efficient than the wild type or R86A insulin receptor in increasing the sensitivity for insulin stimulation of glucose transport. These results indicate that position 86 of the insulin receptor alpha subunit is tolerant to substitution by alanine, but not by proline. Substitution with glycine allows insulin binding, but does not activate normally glucose transport, further supporting an essential role of this position in the initiation of insulin receptor signalling of glucose transport.

Long-term effect of recombinant human insulin-like growth factor I on metabolic and growth control in a patient with leprechaunism

Leprechaunism is the most severe form of insulin resistance, manifesting with abnormal glucose metabolism and retarded growth. In the present study, we investigated the biological actions of recombinant human insulin-like growth factor I (rhIGF-I) in fibroblasts derived from a patient with leprechaunism. In the same patient, we also investigated the pharmacokinetics of IGF-I and the long-term effect of rhIGF-I treatment on metabolic control and physical growth. The patient's fibroblasts showed normal binding of IGF-I, normal phosphorylation of the beta-subunit of the IGF-I receptor, and normal [3H]thymidine incorporation in response to IGF-I. The fibroblast studies suggested that the patient would respond to IGF-I therapy, but certainly did not exclude the possibility of IGF-I resistance in vivo. Administration of recombinant human GH at the dose of 2.0 IU/kg for 3 consecutive days induced a minimal response of serum total IGF-I and IGF-binding protein-3 (IGFBP-3), suggesting partial GH resistance. To increase the serum total IGF-I level, we administered rhIGF-I with combination therapy of intermittent and continuous s.c. injection. This sustained the serum total IGF-I level, but not the serum IGFBP-3 level, within the normal range. The patient was treated with combination therapy of rhIGF-I by both s.c. injection and continuous s.c. infusion for 6 yr and 10 months. Administration of rhIGF-I at total daily dose of 1.6 mg/kg maintained her growth rate and hemoglobin A1c level nearly within the normal range. These findings suggest 1) that this leprechaun patient has an IGF-I-deficient state and partial GH resistance, as reflected by impaired production of IGF-I and IGFBP-3; 2) that rhIGF-I treatment works effectively for preventing postnatal growth retardation and normalizing glucose metabolism in patients with extreme insulin resistance; 3) that this treatment requires relatively higher dose of rhIGF-I; and 4) that treatment appears to be safe and devoid of adverse effects.