1
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Weiss MA, Lawrence MC. A thing of beauty: Structure and function of insulin's "aromatic triplet". Diabetes Obes Metab 2018; 20 Suppl 2:51-63. [PMID: 30230175 PMCID: PMC6159917 DOI: 10.1111/dom.13402] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 05/25/2018] [Accepted: 05/31/2018] [Indexed: 12/30/2022]
Abstract
The classical crystal structure of insulin was determined in 1969 by D.C. Hodgkin et al. following a 35-year program of research. This structure depicted a hexamer remarkable for its self-assembly as a zinc-coordinated trimer of dimer. Prominent at the dimer interface was an "aromatic triplet" of conserved residues at consecutive positions in the B chain: PheB24 , PheB25 and TyrB26 . The elegance of this interface inspired the Oxford team to poetry: "A thing of beauty is a joy forever" (John Keats as quoted by Blundell, T.L., et al. Advances in Protein Chemistry 26:279-286 [1972]). Here, we revisit this aromatic triplet in light of recent advances in the structural biology of insulin bound as a monomer to fragments of the insulin receptor. Such co-crystal structures have defined how these side chains pack at the primary hormone-binding surface of the receptor ectodomain. On receptor binding, the B-chain β-strand (residues B24-B28) containing the aromatic triplet detaches from the α-helical core of the hormone. Whereas TyrB26 lies at the periphery of the receptor interface and may functionally be replaced by a diverse set of substitutions, PheB24 and PheB25 engage invariant elements of receptor domains L1 and αCT. These critical contacts were anticipated by the discovery of diabetes-associated mutations at these positions by Donald Steiner et al. at the University of Chicago. Conservation of PheB24 , PheB25 and TyrB26 among vertebrate insulins reflects the striking confluence of structure-based evolutionary constraints: foldability, protective self-assembly and hormonal activity.
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Affiliation(s)
- Michael A. Weiss
- Department of Biochemistry & Molecular Biology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, IN 46202 USA
| | - Michael C. Lawrence
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, AUSTRALIA
- Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, AUSTRALIA
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2
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Lisgarten DR, Palmer RA, Lobley CMC, Naylor CE, Chowdhry BZ, Al-Kurdi ZI, Badwan AA, Howlin BJ, Gibbons NCJ, Saldanha JW, Lisgarten JN, Basak AK. Ultra-high resolution X-ray structures of two forms of human recombinant insulin at 100 K. Chem Cent J 2017; 11:73. [PMID: 29086855 PMCID: PMC5539060 DOI: 10.1186/s13065-017-0296-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2017] [Accepted: 07/12/2017] [Indexed: 11/30/2022] Open
Abstract
The crystal structure of a commercially available form of human recombinant (HR) insulin, Insugen (I), used in the treatment of diabetes has been determined to 0.92 Å resolution using low temperature, 100 K, synchrotron X-ray data collected at 16,000 keV (λ = 0.77 Å). Refinement carried out with anisotropic displacement parameters, removal of main-chain stereochemical restraints, inclusion of H atoms in calculated positions, and 220 water molecules, converged to a final value of R = 0.1112 and Rfree = 0.1466. The structure includes what is thought to be an ordered propanol molecule (POL) only in chain D(4) and a solvated acetate molecule (ACT) coordinated to the Zn atom only in chain B(2). Possible origins and consequences of the propanol and acetate molecules are discussed. Three types of amino acid representation in the electron density are examined in detail: (i) sharp with very clearly resolved features; (ii) well resolved but clearly divided into two conformations which are well behaved in the refinement, both having high quality geometry; (iii) poor density and difficult or impossible to model. An example of type (ii) is observed for the intra-chain disulphide bridge in chain C(3) between Sγ6–Sγ11 which has two clear conformations with relative refined occupancies of 0.8 and 0.2, respectively. In contrast the corresponding S–S bridge in chain A(1) shows one clearly defined conformation. A molecular dynamics study has provided a rational explanation of this difference between chains A and C. More generally, differences in the electron density features between corresponding residues in chains A and C and chains B and D is a common observation in the Insugen (I) structure and these effects are discussed in detail. The crystal structure, also at 0.92 Å and 100 K, of a second commercially available form of human recombinant insulin, Intergen (II), deposited in the Protein Data Bank as 3W7Y which remains otherwise unpublished is compared here with the Insugen (I) structure. In the Intergen (II) structure there is no solvated propanol or acetate molecule. The electron density of Intergen (II), however, does also exhibit the three types of amino acid representations as in Insugen (I). These effects do not necessarily correspond between chains A and C or chains B and D in Intergen (II), or between corresponding residues in Insugen (I). The results of this comparison are reported.Conformations of PheB25 and PheD25 in three insulin structures: implications for biological activity? Insulin residues PheB25 and PheD25 are considered to be important for insulin receptor binding and changes in biological activity occur when these residues are modified. In porcine insulin and Intergen (II) PheB25 adopts conformation B and PheD25 conformation D. However, unexpectedly PheB25 in Insugen (I) human recombinant insulin adopts two distinct conformations corresponding to B and D, Figure 1 and PheD25 adopts a single conformation corresponding to B not D, Figure 2. Conformations of this residue in the ultra-high resolution structure of Insugen (I) are therefore unique within this set. Figures were produced with Biovia, Discovery Studio 2016. ![]()
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Affiliation(s)
- David R Lisgarten
- Biomolecular Research Group, School of Human and Life Sciences, Canterbury Christ Church University, North Holmes Road, Canterbury, Kent, CT1 1QU, UK
| | - Rex A Palmer
- Department of Crystallography, Biochemical Sciences, Birkbeck College, Malet St, London, WC1E7HX, UK.
| | - Carina M C Lobley
- Diamond Light Source Ltd, Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK
| | - Claire E Naylor
- Molecular Dimensions Ltd, Unit 6, Goodwin Business Park, Willie Snaith Road, Newmarket, Suffolk, CB8 7SQ, UK
| | - Babur Z Chowdhry
- Faculty of Engineering & Science, University of Greenwich (Medway Campus), Chatham Maritime, Kent, ME4 4TB, UK
| | - Zakieh I Al-Kurdi
- The Jordanian Pharmaceutical Manufacturing Company (PLC), Suwagh Subsidiary for Drug Delivery Systems, P.O. Box 94, Naor, 11710, Jordan
| | - Adnan A Badwan
- The Jordanian Pharmaceutical Manufacturing Company (PLC), Suwagh Subsidiary for Drug Delivery Systems, P.O. Box 94, Naor, 11710, Jordan
| | - Brendan J Howlin
- Chemical Sciences Division, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey, GU2 7HX, UK
| | - Nicholas C J Gibbons
- Department of Natural Sciences, School of Science and Technology, University of Middlesex, Hendon Campus, The Burroughs, London, NW4 4BT, UK
| | - José W Saldanha
- MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW71AA, UK
| | - John N Lisgarten
- Faculty of Engineering & Science, University of Greenwich (Medway Campus), Chatham Maritime, Kent, ME4 4TB, UK
| | - Ajit K Basak
- Department of Crystallography, Biochemical Sciences, Birkbeck College, Malet St, London, WC1E7HX, UK
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3
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Inversion of the Side-Chain Stereochemistry of Indvidual Thr or Ile Residues in a Protein Molecule: Impact on the Folding, Stability, and Structure of the ShK Toxin. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201612398] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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4
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Dang B, Shen R, Kubota T, Mandal K, Bezanilla F, Roux B, Kent SBH. Inversion of the Side-Chain Stereochemistry of Indvidual Thr or Ile Residues in a Protein Molecule: Impact on the Folding, Stability, and Structure of the ShK Toxin. Angew Chem Int Ed Engl 2017; 56:3324-3328. [PMID: 28194851 DOI: 10.1002/anie.201612398] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Indexed: 11/05/2022]
Abstract
ShK toxin is a cysteine-rich 35-residue protein ion-channel ligand isolated from the sea anemone Stichodactyla helianthus. In this work, we studied the effect of inverting the side chain stereochemistry of individual Thr or Ile residues on the properties of the ShK protein. Molecular dynamics simulations were used to calculate the free energy cost of inverting the side-chain stereochemistry of individual Thr or Ile residues. Guided by the computational results, we used chemical protein synthesis to prepare three ShK polypeptide chain analogues, each containing either an allo-Thr or an allo-Ile residue. The three allo-Thr or allo-Ile-containing ShK polypeptides were able to fold into defined protein products, but with different folding propensities. Their relative thermal stabilities were measured and were consistent with the MD simulation data. Structures of the three ShK analogue proteins were determined by quasi-racemic X-ray crystallography and were similar to wild-type ShK. All three ShK analogues retained ion-channel blocking activity.
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Affiliation(s)
- Bobo Dang
- Department of Chemistry, Department of Biochemistry & Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, 60637, USA
| | - Rong Shen
- Department of Biochemistry & Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, 60637, USA
| | - Tomoya Kubota
- Department of Biochemistry & Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, 60637, USA
| | - Kalyaneswar Mandal
- Department of Chemistry, Department of Biochemistry & Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, 60637, USA
| | - Francisco Bezanilla
- Department of Biochemistry & Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, 60637, USA
| | - Benoit Roux
- Department of Biochemistry & Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, 60637, USA
| | - Stephen B H Kent
- Department of Chemistry, Department of Biochemistry & Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, 60637, USA
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5
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Islam MA, Bhayye S, Adeniyi AA, Soliman ME, Pillay TS. Diabetes mellitus caused by mutations in human insulin: analysis of impaired receptor binding of insulins Wakayama, Los Angeles and Chicago using pharmacoinformatics. J Biomol Struct Dyn 2016; 35:724-737. [DOI: 10.1080/07391102.2016.1160258] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Md Ataul Islam
- Faculty of Health Sciences, Department of Chemical Pathology, & Institute of Cellular & Molecular Medicine, University of Pretoria and National Health Laboratory Service Tshwane Academic Division, Pretoria, South Africa
| | - Sagar Bhayye
- Department of Chemical Technology, University of Calcutta, 92, A. P. C. Road, Kolkata 700009, India
| | - Adebayo A. Adeniyi
- Discipline of Pharmaceutical Sciences, School of Health Sciences, University of KwaZulu-Natal, Durban 4000, South Africa
| | - Mahmoud E.S. Soliman
- Discipline of Pharmaceutical Sciences, School of Health Sciences, University of KwaZulu-Natal, Durban 4000, South Africa
| | - Tahir S. Pillay
- Faculty of Health Sciences, Department of Chemical Pathology, & Institute of Cellular & Molecular Medicine, University of Pretoria and National Health Laboratory Service Tshwane Academic Division, Pretoria, South Africa
- Division of Chemical Pathology, University of Cape Town, Cape Town, South Africa
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6
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Liu M, Haataja L, Wright J, Wickramasinghe NP, Hua QX, Phillips NF, Barbetti F, Weiss MA, Arvan P. Mutant INS-gene induced diabetes of youth: proinsulin cysteine residues impose dominant-negative inhibition on wild-type proinsulin transport. PLoS One 2010; 5:e13333. [PMID: 20948967 PMCID: PMC2952628 DOI: 10.1371/journal.pone.0013333] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Accepted: 09/13/2010] [Indexed: 02/06/2023] Open
Abstract
Recently, a syndrome of Mutant INS-gene-induced Diabetes of Youth (MIDY, derived from one of 26 distinct mutations) has been identified as a cause of insulin-deficient diabetes, resulting from expression of a misfolded mutant proinsulin protein in the endoplasmic reticulum (ER) of insulin-producing pancreatic beta cells. Genetic deletion of one, two, or even three alleles encoding insulin in mice does not necessarily lead to diabetes. Yet MIDY patients are INS-gene heterozygotes; inheritance of even one MIDY allele, causes diabetes. Although a favored explanation for the onset of diabetes is that insurmountable ER stress and ER stress response from the mutant proinsulin causes a net loss of beta cells, in this report we present three surprising and interlinked discoveries. First, in the presence of MIDY mutants, an increased fraction of wild-type proinsulin becomes recruited into nonnative disulfide-linked protein complexes. Second, regardless of whether MIDY mutations result in the loss, or creation, of an extra unpaired cysteine within proinsulin, Cys residues in the mutant protein are nevertheless essential in causing intracellular entrapment of co-expressed wild-type proinsulin, blocking insulin production. Third, while each of the MIDY mutants induces ER stress and ER stress response; ER stress and ER stress response alone appear insufficient to account for blockade of wild-type proinsulin. While there is general agreement that ultimately, as diabetes progresses, a significant loss of beta cell mass occurs, the early events described herein precede cell death and loss of beta cell mass. We conclude that the molecular pathogenesis of MIDY is initiated by perturbation of the disulfide-coupled folding pathway of wild-type proinsulin.
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Affiliation(s)
- Ming Liu
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan, United States of America
| | - Leena Haataja
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan, United States of America
| | - Jordan Wright
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan, United States of America
| | - Nalinda P. Wickramasinghe
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, United States of America
| | - Qing-Xin Hua
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, United States of America
| | - Nelson F. Phillips
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, United States of America
| | - Fabrizio Barbetti
- Laboratory of Molecular Endocrinology and Metabolism, Bambino Gesù Children's Hospital, Scientific Institute (IRCCS), Rome, Italy
- Department of Internal Medicine, University of Tor Vergata, Rome, Italy
| | - Michael A. Weiss
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, United States of America
- * E-mail: (PA); (MAW)
| | - Peter Arvan
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan, United States of America
- * E-mail: (PA); (MAW)
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7
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Liu M, Hua QX, Hu SQ, Jia W, Yang Y, Saith SE, Whittaker J, Arvan P, Weiss MA. Deciphering the hidden informational content of protein sequences: foldability of proinsulin hinges on a flexible arm that is dispensable in the mature hormone. J Biol Chem 2010; 285:30989-1001. [PMID: 20663888 PMCID: PMC2945590 DOI: 10.1074/jbc.m110.152645] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Revised: 07/21/2010] [Indexed: 01/28/2023] Open
Abstract
Protein sequences encode both structure and foldability. Whereas the interrelationship of sequence and structure has been extensively investigated, the origins of folding efficiency are enigmatic. We demonstrate that the folding of proinsulin requires a flexible N-terminal hydrophobic residue that is dispensable for the structure, activity, and stability of the mature hormone. This residue (Phe(B1) in placental mammals) is variably positioned within crystal structures and exhibits (1)H NMR motional narrowing in solution. Despite such flexibility, its deletion impaired insulin chain combination and led in cell culture to formation of non-native disulfide isomers with impaired secretion of the variant proinsulin. Cellular folding and secretion were maintained by hydrophobic substitutions at B1 but markedly perturbed by polar or charged side chains. We propose that, during folding, a hydrophobic side chain at B1 anchors transient long-range interactions by a flexible N-terminal arm (residues B1-B8) to mediate kinetic or thermodynamic partitioning among disulfide intermediates. Evidence for the overall contribution of the arm to folding was obtained by alanine scanning mutagenesis. Together, our findings demonstrate that efficient folding of proinsulin requires N-terminal sequences that are dispensable in the native state. Such arm-dependent folding can be abrogated by mutations associated with β-cell dysfunction and neonatal diabetes mellitus.
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Affiliation(s)
- Ming Liu
- From the Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan 48109 and
| | - Qing-xin Hua
- the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Shi-Quan Hu
- the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Wenhua Jia
- the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Yanwu Yang
- the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Sunil Evan Saith
- From the Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan 48109 and
| | - Jonathan Whittaker
- the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Peter Arvan
- From the Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan 48109 and
| | - Michael A. Weiss
- the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
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8
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Thorsøe KS, Schlein M, Steensgaard DB, Brandt J, Schluckebier G, Naver H. Kinetic Evidence for the Sequential Association of Insulin Binding Sites 1 and 2 to the Insulin Receptor and the Influence of Receptor Isoform,. Biochemistry 2010; 49:6234-46. [DOI: 10.1021/bi1000118] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
| | - Morten Schlein
- Diabetes Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, 2760 Måløv, Denmark
| | | | - Jakob Brandt
- Diabetes Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, 2760 Måløv, Denmark
| | - Gerd Schluckebier
- Diabetes Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, 2760 Måløv, Denmark
| | - Helle Naver
- Diabetes Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, 2760 Måløv, Denmark
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9
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Yang Y, Hua QX, Liu J, Shimizu EH, Choquette MH, Mackin RB, Weiss MA. Solution structure of proinsulin: connecting domain flexibility and prohormone processing. J Biol Chem 2010; 285:7847-51. [PMID: 20106974 PMCID: PMC2832934 DOI: 10.1074/jbc.c109.084921] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Revised: 01/13/2010] [Indexed: 12/21/2022] Open
Abstract
The folding of proinsulin, the single-chain precursor of insulin, ensures native disulfide pairing in pancreatic beta-cells. Mutations that impair folding cause neonatal diabetes mellitus. Although the classical structure of insulin is well established, proinsulin is refractory to crystallization. Here, we employ heteronuclear NMR spectroscopy to characterize a monomeric analogue. Proinsulin contains a native-like insulin moiety (A- and B-domains); the tethered connecting (C) domain (as probed by {(1)H}-(15)N nuclear Overhauser enhancements) is progressively less ordered. Although the BC junction is flexible, residues near the CA junction exhibit alpha-helical-like features. Relative to canonical alpha-helices, however, segmental (13)C(alpha/beta) chemical shifts are attenuated, suggesting that this junction and contiguous A-chain residues are molten. We propose that flexibility at each C-domain junction facilitates prohormone processing. Studies of protease SPC3 (PC1/3) suggest that C-domain sequences contribute to cleavage site selection. The structure of proinsulin provides a foundation for studies of insulin biosynthesis and its impairment in monogenic forms of diabetes mellitus.
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Affiliation(s)
- Yanwu Yang
- From the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106 and
| | - Qing-xin Hua
- From the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106 and
| | - Jin Liu
- the Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178
| | - Eri H. Shimizu
- the Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178
| | - Meredith H. Choquette
- the Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178
| | - Robert B. Mackin
- the Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178
| | - Michael A. Weiss
- From the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106 and
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10
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Nakamura T, Takahashi H, Takahashi M, Shimba N, Suzuki EI, Shimada I. Direct Determination of the Insulin−Insulin Receptor Interface Using Transferred Cross-Saturation Experiments. J Med Chem 2010; 53:1917-22. [DOI: 10.1021/jm901099v] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Takefumi Nakamura
- The Institute of Life Sciences, Ajinomoto Co. Inc., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, Kanagawa, Japan
- Japan Biological Informatics Consortium, 2-41-6 Aomi, Koto-ku, Tokyo, Japan
- Biomedicinal Information Research Center, National institute of Advanced Industrial Science and Technology, 2-41-6 Aomi, Koto-ku, Tokyo, Japan
| | - Hideo Takahashi
- Biomedicinal Information Research Center, National institute of Advanced Industrial Science and Technology, 2-41-6 Aomi, Koto-ku, Tokyo, Japan
| | - Mitsuo Takahashi
- The Institute of Life Sciences, Ajinomoto Co. Inc., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, Kanagawa, Japan
| | - Nobuhisa Shimba
- The Institute of Life Sciences, Ajinomoto Co. Inc., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, Kanagawa, Japan
- Japan Biological Informatics Consortium, 2-41-6 Aomi, Koto-ku, Tokyo, Japan
- Biomedicinal Information Research Center, National institute of Advanced Industrial Science and Technology, 2-41-6 Aomi, Koto-ku, Tokyo, Japan
| | - Ei-ichiro Suzuki
- The Institute of Life Sciences, Ajinomoto Co. Inc., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, Kanagawa, Japan
- Japan Biological Informatics Consortium, 2-41-6 Aomi, Koto-ku, Tokyo, Japan
| | - Ichio Shimada
- Biomedicinal Information Research Center, National institute of Advanced Industrial Science and Technology, 2-41-6 Aomi, Koto-ku, Tokyo, Japan
- The Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
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11
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Implications for the active form of human insulin based on the structural convergence of highly active hormone analogues. Proc Natl Acad Sci U S A 2010; 107:1966-70. [PMID: 20133841 DOI: 10.1073/pnas.0911785107] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Insulin is a key protein hormone that regulates blood glucose levels and, thus, has widespread impact on lipid and protein metabolism. Insulin action is manifested through binding of its monomeric form to the Insulin Receptor (IR). At present, however, our knowledge about the structural behavior of insulin is based upon inactive, multimeric, and storage-like states. The active monomeric structure, when in complex with the receptor, must be different as the residues crucial for the interactions are buried within the multimeric forms. Although the exact nature of the insulin's induced-fit is unknown, there is strong evidence that the C-terminal part of the B-chain is a dynamic element in insulin activation and receptor binding. Here, we present the design and analysis of highly active (200-500%) insulin analogues that are truncated at residue 26 of the B-chain (B(26)). They show a structural convergence in the form of a new beta-turn at B(24)-B(26). We propose that the key element in insulin's transition, from an inactive to an active state, may be the formation of the beta-turn at B(24)-B(26) associated with a trans to cis isomerisation at the B(25)-B(26) peptide bond. Here, this turn is achieved with N-methylated L-amino acids adjacent to the trans to cis switch at the B(25)-B(26) peptide bond or by the insertion of certain D-amino acids at B(26). The resultant conformational changes unmask previously buried amino acids that are implicated in IR binding and provide structural details for new approaches in rational design of ligands effective in combating diabetes.
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12
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Xu B, Huang K, Chu YC, Hu SQ, Nakagawa S, Wang S, Wang RY, Whittaker J, Katsoyannis PG, Weiss MA. Decoding the cryptic active conformation of a protein by synthetic photoscanning: insulin inserts a detachable arm between receptor domains. J Biol Chem 2009; 284:14597-608. [PMID: 19321435 PMCID: PMC2682907 DOI: 10.1074/jbc.m900087200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2009] [Revised: 03/20/2009] [Indexed: 12/15/2022] Open
Abstract
Proteins evolve in a fitness landscape encompassing a complex network of biological constraints. Because of the interrelation of folding, function, and regulation, the ground-state structure of a protein may be inactive. A model is provided by insulin, a vertebrate hormone central to the control of metabolism. Whereas native assembly mediates storage within pancreatic beta-cells, the active conformation of insulin and its mode of receptor binding remain elusive. Here, functional surfaces of insulin were probed by photocross-linking of an extensive set of azido derivatives constructed by chemical synthesis. Contacts are circumferential, suggesting that insulin is encaged within its receptor. Mapping of photoproducts to the hormone-binding domains of the insulin receptor demonstrated alternating contacts by the B-chain beta-strand (residues B24-B28). Whereas even-numbered probes (at positions B24 and B26) contact the N-terminal L1 domain of the alpha-subunit, odd-numbered probes (at positions B25 and B27) contact its C-terminal insert domain. This alternation corresponds to the canonical structure of abeta-strand (wherein successive residues project in opposite directions) and so suggests that the B-chain inserts between receptor domains. Detachment of a receptor-binding arm enables photo engagement of surfaces otherwise hidden in the free hormone. The arm and associated surfaces contain sites also required for nascent folding and self-assembly of storage hexamers. The marked compression of structural information within a short polypeptide sequence rationalizes the diversity of diabetes-associated mutations in the insulin gene. Our studies demonstrate that photoscanning mutagenesis can decode the active conformation of a protein and so illuminate cryptic constraints underlying its evolution.
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Affiliation(s)
- Bin Xu
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA
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13
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Hua QX, Xu B, Huang K, Hu SQ, Nakagawa S, Jia W, Wang S, Whittaker J, Katsoyannis PG, Weiss MA. Enhancing the activity of a protein by stereospecific unfolding: conformational life cycle of insulin and its evolutionary origins. J Biol Chem 2009; 284:14586-96. [PMID: 19321436 DOI: 10.1074/jbc.m900085200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A central tenet of molecular biology holds that the function of a protein is mediated by its structure. An inactive ground-state conformation may nonetheless be enjoined by the interplay of competing biological constraints. A model is provided by insulin, well characterized at atomic resolution by x-ray crystallography. Here, we demonstrate that the activity of the hormone is enhanced by stereospecific unfolding of a conserved structural element. A bifunctional beta-strand mediates both self-assembly (within beta-cell storage vesicles) and receptor binding (in the bloodstream). This strand is anchored by an invariant side chain (Phe(B24)); its substitution by Ala leads to an unstable but native-like analog of low activity. Substitution by d-Ala is equally destabilizing, and yet the protein diastereomer exhibits enhanced activity with segmental unfolding of the beta-strand. Corresponding photoactivable derivatives (containing l- or d-para-azido-Phe) cross-link to the insulin receptor with higher d-specific efficiency. Aberrant exposure of hydrophobic surfaces in the analogs is associated with accelerated fibrillation, a form of aggregation-coupled misfolding associated with cellular toxicity. Conservation of Phe(B24), enforced by its dual role in native self-assembly and induced fit, thus highlights the implicit role of misfolding as an evolutionary constraint. Whereas classical crystal structures of insulin depict its storage form, signaling requires engagement of a detachable arm at an extended receptor interface. Because this active conformation resembles an amyloidogenic intermediate, we envisage that induced fit and self-assembly represent complementary molecular adaptations to potential proteotoxicity. The cryptic threat of misfolding poses a universal constraint in the evolution of polypeptide sequences.
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Affiliation(s)
- Qing-xin Hua
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA
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14
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Abstract
Crystal structures of insulin are remarkable for a long-range reorganization among three families of hexamers (designated T(6), T(3)R(3)(f), and R(6)). Although these structures are well characterized at atomic resolution, the biological implications of the TR transition remain the subject of speculation. Recent studies indicate that such allostery reflects a structural switch between distinct folding-competent and active conformations. Stereospecific modulation of this switch by corresponding d- and l-amino-acid substitutions yields reciprocal effects on protein stability and receptor-binding activity. Naturally occurring human mutations at the site of conformational change impair the folding of proinsulin and cause permanent neonatal-onset diabetes mellitus. The repertoire of classical structures thus foreshadows the conformational lifecycle of insulin in vivo. By highlighting the richness of information provided by protein crystallography-even in a biological realm far removed from conditions of crystallization-these findings validate the prescient insights of the late D. C. Hodgkin. Future studies of the receptor-bound structure of insulin may enable design of novel agonists for the treatment of diabetes mellitus.
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15
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Wan ZL, Huang K, Hu SQ, Whittaker J, Weiss MA. The structure of a mutant insulin uncouples receptor binding from protein allostery. An electrostatic block to the TR transition. J Biol Chem 2008; 283:21198-210. [PMID: 18492668 PMCID: PMC2475698 DOI: 10.1074/jbc.m800235200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2008] [Revised: 05/01/2008] [Indexed: 11/06/2022] Open
Abstract
The zinc insulin hexamer undergoes allosteric reorganization among three conformational states, designated T(6), T(3)R(3)(f), and R(6). Although the free monomer in solution (the active species) resembles the classical T-state, an R-like conformational change is proposed to occur upon receptor binding. Here, we distinguish between the conformational requirements of receptor binding and the crystallographic TR transition by design of an active variant refractory to such reorganization. Our strategy exploits the contrasting environments of His(B5) in wild-type structures: on the T(6) surface but within an intersubunit crevice in R-containing hexamers. The TR transition is associated with a marked reduction in His(B5) pK(a), in turn predicting that a positive charge at this site would destabilize the R-specific crevice. Remarkably, substitution of His(B5) (conserved among eutherian mammals) by Arg (occasionally observed among other vertebrates) blocks the TR transition, as probed in solution by optical spectroscopy. Similarly, crystallization of Arg(B5)-insulin in the presence of phenol (ordinarily a potent inducer of the TR transition) yields T(6) hexamers rather than R(6) as obtained in control studies of wild-type insulin. The variant structure, determined at a resolution of 1.3A, closely resembles the wild-type T(6) hexamer. Whereas Arg(B5) is exposed on the protein surface, its side chain participates in a solvent-stabilized network of contacts similar to those involving His(B5) in wild-type T-states. The substantial receptor-binding activity of Arg(B5)-insulin (40% relative to wild type) demonstrates that the function of an insulin monomer can be uncoupled from its allosteric reorganization within zinc-stabilized hexamers.
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Affiliation(s)
- Zhu-li Wan
- Departments of Biochemistry
and Nutrition, Case Western Reserve
University School of Medicine, Cleveland, Ohio 44106
| | - Kun Huang
- Departments of Biochemistry
and Nutrition, Case Western Reserve
University School of Medicine, Cleveland, Ohio 44106
| | - Shi-Quan Hu
- Departments of Biochemistry
and Nutrition, Case Western Reserve
University School of Medicine, Cleveland, Ohio 44106
| | - Jonathan Whittaker
- Departments of Biochemistry
and Nutrition, Case Western Reserve
University School of Medicine, Cleveland, Ohio 44106
| | - Michael A. Weiss
- Departments of Biochemistry
and Nutrition, Case Western Reserve
University School of Medicine, Cleveland, Ohio 44106
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16
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Žáková L, Kazdová L, Hančlová I, Protivínská E, Šanda M, Buděšínský M, Jiráček J. Insulin Analogues with Modifications at Position B26. Divergence of Binding Affinity and Biological Activity. Biochemistry 2008; 47:5858-68. [DOI: 10.1021/bi702086w] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Lenka Žáková
- Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic, and Institute for Clinical and Experimental Medicine, Vídeňská 1958/9, 140 21 Praha 4, Czech Republic
| | - Ludmila Kazdová
- Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic, and Institute for Clinical and Experimental Medicine, Vídeňská 1958/9, 140 21 Praha 4, Czech Republic
| | - Ivona Hančlová
- Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic, and Institute for Clinical and Experimental Medicine, Vídeňská 1958/9, 140 21 Praha 4, Czech Republic
| | - Eva Protivínská
- Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic, and Institute for Clinical and Experimental Medicine, Vídeňská 1958/9, 140 21 Praha 4, Czech Republic
| | - Miloslav Šanda
- Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic, and Institute for Clinical and Experimental Medicine, Vídeňská 1958/9, 140 21 Praha 4, Czech Republic
| | - Miloš Buděšínský
- Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic, and Institute for Clinical and Experimental Medicine, Vídeňská 1958/9, 140 21 Praha 4, Czech Republic
| | - Jiří Jiráček
- Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic, and Institute for Clinical and Experimental Medicine, Vídeňská 1958/9, 140 21 Praha 4, Czech Republic
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17
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Glendorf T, Sørensen AR, Nishimura E, Pettersson I, Kjeldsen T. Importance of the solvent-exposed residues of the insulin B chain alpha-helix for receptor binding. Biochemistry 2008; 47:4743-51. [PMID: 18376848 DOI: 10.1021/bi800054z] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Conjointly, the solvent-exposed residues of the central alpha-helix of the B chain form a well-defined ridge, which is flanked and partly overlapped by the two described insulin receptor binding surfaces on either side of the insulin molecule. To evaluate the importance of this interface in insulin receptor binding, we developed a new powerful method that allows us to introduce all the naturally occurring amino acids into a given position and subsequently determine the receptor binding affinities of the resulting insulin analogues. The total amino acid scanning mutagenesis was performed at positions B9, B10, B12, B13, B16, and B17, and the vast majority of the insulin analogue precursors were expressed and secreted in amounts close to that of the wild-type (human insulin) precursor. The analogue binding data revealed that positions B12 and B16 were the two positions most affected by the amino acid substitutions. Interestingly, the receptor binding affinities of the B13 analogues were also markedly affected by the amino acid substitutions, suggesting that GluB13 indeed is a part of insulin's binding surface. The B10 library screen generated analogues covering a wide range of (20-340%) of relative binding affinities, and the results indicated that a structural stabilization of the central alpha-helix and thereby a more rigid presentation of the binding epitope at the insulin receptor is important for receptor recognition. In conclusion, systematic amino acid scanning mutagenesis allowed us to confirm the importance of the B chain alpha-helix as a central recognition element serving as a linker of a continual binding surface.
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Affiliation(s)
- Tine Glendorf
- Diabetes Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Måløv, Denmark.
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18
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Hua QX, Nakagawa SH, Jia W, Huang K, Phillips NB, Hu SQ, Weiss MA. Design of an active ultrastable single-chain insulin analog: synthesis, structure, and therapeutic implications. J Biol Chem 2008; 283:14703-16. [PMID: 18332129 DOI: 10.1074/jbc.m800313200] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Single-chain insulin (SCI) analogs provide insight into the inter-relation of hormone structure, function, and dynamics. Although compatible with wild-type structure, short connecting segments (<3 residues) prevent induced fit upon receptor binding and so are essentially without biological activity. Substantial but incomplete activity can be regained with increasing linker length. Here, we describe the design, structure, and function of a single-chain insulin analog (SCI-57) containing a 6-residue linker (GGGPRR). Native receptor-binding affinity (130 +/- 8% relative to the wild type) is achieved as hindrance by the linker is offset by favorable substitutions in the insulin moiety. The thermodynamic stability of SCI-57 is markedly increased (DeltaDeltaG(u) = 0.7 +/- 0.1 kcal/mol relative to the corresponding two-chain analog and 1.9 +/- 0.1 kcal/mol relative to wild-type insulin). Analysis of inter-residue nuclear Overhauser effects demonstrates that a native-like fold is maintained in solution. Surprisingly, the glycine-rich connecting segment folds against the insulin moiety: its central Pro contacts Val(A3) at the edge of the hydrophobic core, whereas the final Arg extends the A1-A8 alpha-helix. Comparison between SCI-57 and its parent two-chain analog reveals striking enhancement of multiple native-like nuclear Overhauser effects within the tethered protein. These contacts are consistent with wild-type crystal structures but are ordinarily attenuated in NMR spectra of two-chain analogs, presumably due to conformational fluctuations. Linker-specific damping of fluctuations provides evidence for the intrinsic flexibility of an insulin monomer. In addition to their biophysical interest, ultrastable SCIs may enhance the safety and efficacy of insulin replacement therapy in the developing world.
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Affiliation(s)
- Qing-xin Hua
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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19
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Abstract
Throughout much of the last century insulin served a central role in the advancement of peptide chemistry, pharmacology, cell signaling and structural biology. These discoveries have provided a steadily improved quantity and quality of life for those afflicted with diabetes. The collective work serves as a foundation for the development of insulin analogs and mimetics capable of providing more tailored therapy. Advancements in patient care have been paced by breakthroughs in core technologies, such as semisynthesis, high performance chromatography, rDNA-biosynthesis and formulation sciences. How the structural and conformational dynamics of this endocrine hormone elicit its biological response remains a vigorous area of study. Numerous insulin analogs have served to coordinate structural biology and biochemical signaling to provide a first level understanding of insulin action. The introduction of broad chemical diversity to the study of insulin has been limited by the inefficiency in total chemical synthesis, and the inherent limitations in rDNA-biosynthesis and semisynthetic approaches. The goals of continued investigation remain the delivery of insulin therapy where glycemic control is more precise and hypoglycemic liability is minimized. Additional objectives for medicinal chemists are the identification of superagonists and insulins more suitable for non-injectable delivery. The historical advancements in the synthesis of insulin analogs by multiple methods is reviewed with the specific structural elements of critical importance being highlighted. The functional refinement of this hormone as directed to improved patient care with insulin analogs of more precise pharmacology is reported.
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Affiliation(s)
- John P Mayer
- Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, IN 46285, USA
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20
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Sohma Y, Pentelute B, Whittaker J, Hua QX, Whittaker L, Weiss M, Kent S. Comparative Properties of Insulin-like Growth Factor 1 (IGF-1) and [Gly7D-Ala]IGF-1 Prepared by Total Chemical Synthesis. Angew Chem Int Ed Engl 2008; 47:1102-6. [DOI: 10.1002/anie.200703521] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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21
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Sohma Y, Pentelute B, Whittaker J, Hua QX, Whittaker L, Weiss M, Kent S. Comparative Properties of Insulin-like Growth Factor 1 (IGF-1) and [Gly7D-Ala]IGF-1 Prepared by Total Chemical Synthesis. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200703521] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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22
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Huang K, Chan SJ, Hua QX, Chu YC, Wang RY, Klaproth B, Jia W, Whittaker J, De Meyts P, Nakagawa SH, Steiner DF, Katsoyannis PG, Weiss MA. The A-chain of Insulin Contacts the Insert Domain of the Insulin Receptor. J Biol Chem 2007; 282:35337-49. [PMID: 17884811 DOI: 10.1074/jbc.m705996200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The contribution of the insulin A-chain to receptor binding is investigated by photo-cross-linking and nonstandard mutagenesis. Studies focus on the role of Val(A3), which projects within a crevice between the A- and B-chains. Engineered receptor alpha-subunits containing specific protease sites ("midi-receptors") are employed to map the site of photo-cross-linking by an analog containing a photoactivable A3 side chain (para-azido-Phe (Pap)). The probe cross-links to a C-terminal peptide (residues 703-719 of the receptor A isoform, KTFEDYLHNVVFVPRPS) containing side chains critical for hormone binding (underlined); the corresponding segment of the holoreceptor was shown previously to cross-link to a Pap(B25)-insulin analog. Because Pap is larger than Val and so may protrude beyond the A3-associated crevice, we investigated analogs containing A3 substitutions comparable in size to Val as follows: Thr, allo-Thr, and alpha-aminobutyric acid (Aba). Substitutions were introduced within an engineered monomer. Whereas previous studies of smaller substitutions (Gly(A3) and Ser(A3)) encountered nonlocal conformational perturbations, NMR structures of the present analogs are similar to wild-type insulin; the variant side chains are accommodated within a native-like crevice with minimal distortion. Receptor binding activities of Aba(A3) and allo-Thr(A3) analogs are reduced at least 10-fold; the activity of Thr(A3)-DKP-insulin is reduced 5-fold. The hormone-receptor interface is presumably destabilized either by a packing defect (Aba(A3)) or by altered polarity (allo-Thr(A3) and Thr(A3)). Our results provide evidence that Val(A3), a site of mutation causing diabetes mellitus, contacts the insert domain-derived tail of the alpha-subunit in a hormone-receptor complex.
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Affiliation(s)
- Kun Huang
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA
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23
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Abstract
One of the predominant aims of insulin therapy for diabetes is to appropriately mimic physiological insulin secretion levels and their correlation with glucose concentration in healthy individuals. This report outlines current methods and their limitations in glycemic control and their possible relationship to insufficient knowledge about the structure and dynamics of the insulin hormone itself. Based on recent experimental and computational work, a possible approach to less-invasive insulin administration is sketched.
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Affiliation(s)
- Manuela Koch
- Department of Chemistry, University of Basel, Basel, Switzerland
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24
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Lou M, Garrett TPJ, McKern NM, Hoyne PA, Epa VC, Bentley JD, Lovrecz GO, Cosgrove LJ, Frenkel MJ, Ward CW. The first three domains of the insulin receptor differ structurally from the insulin-like growth factor 1 receptor in the regions governing ligand specificity. Proc Natl Acad Sci U S A 2006; 103:12429-34. [PMID: 16894147 PMCID: PMC1533800 DOI: 10.1073/pnas.0605395103] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
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.
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MESH Headings
- Amino Acid Sequence
- Animals
- CHO Cells
- Cricetinae
- Crystallography, X-Ray
- Humans
- Insulin-Like Growth Factor I/chemistry
- Insulin-Like Growth Factor I/genetics
- Insulin-Like Growth Factor I/metabolism
- Ligands
- Models, Molecular
- Molecular Sequence Data
- Mutation
- Protein Binding
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Receptor, IGF Type 1/chemistry
- Receptor, IGF Type 1/genetics
- Receptor, IGF Type 1/metabolism
- Receptor, Insulin/chemistry
- Receptor, Insulin/genetics
- Receptor, Insulin/metabolism
- Sequence Alignment
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Affiliation(s)
- Meizhen Lou
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
| | - Thomas P. J. Garrett
- Walter and Eliza Hall Institute for Medical Research, Post Office, Royal Melbourne Hospital, Parkville, Victoria 3050, Australia
- To whom correspondence may be addressed. E-mail:
or
| | - Neil M. McKern
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
| | - Peter A. Hoyne
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
| | - V. Chandana Epa
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
| | - John D. Bentley
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
| | - George O. Lovrecz
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
| | - Leah J. Cosgrove
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
| | - Maurice J. Frenkel
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
| | - Colin W. Ward
- *Division of Molecular and Health Technologies, Commonwealth Scientific and Industrial Research Organization, 343 Royal Parade, Parkville, Victoria 3052, Australia; and
- To whom correspondence may be addressed. E-mail:
or
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25
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Hua QX, Nakagawa S, Hu SQ, Jia W, Wang S, Weiss MA. Toward the active conformation of insulin: stereospecific modulation of a structural switch in the B chain. J Biol Chem 2006; 281:24900-9. [PMID: 16762918 DOI: 10.1074/jbc.m602691200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
How insulin binds to the insulin receptor has long been a subject of speculation. Although the structure of the free hormone has been extensively characterized, a variety of evidence suggests that a conformational change occurs upon receptor binding. Here, we employ chiral mutagenesis, comparison of corresponding d and l amino acid substitutions, to investigate a possible switch in the B-chain. To investigate the interrelation of structure, function, and stability, isomeric analogs have been synthesized in which an invariant glycine in a beta-turn (Gly(B8)) is replaced by d- or l-Ser. The d substitution enhances stability (DeltaDeltaG(u) 0.9 kcal/mol) but impairs receptor binding by 100-fold; by contrast, the l substitution markedly impairs stability (DeltaDeltaG(u) -3.0 kcal/mol) with only 2-fold reduction in receptor binding. Although the isomeric structures each retain a native-like overall fold, the l-Ser(B8) analog exhibits fewer helix-related and long range nuclear Overhauser effects than does the d-Ser(B8) analog or native monomer. Evidence for enhanced conformational fluctuations in the unstable analog is provided by its attenuated CD spectrum. The inverse relationship between stereospecific stabilization and receptor binding strongly suggests that the B7-B10 beta-turn changes conformation on receptor binding.
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Affiliation(s)
- Qing-Xin Hua
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA
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26
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Nakagawa SH, Hua QX, Hu SQ, Jia W, Wang S, Katsoyannis PG, Weiss MA. Chiral mutagenesis of insulin. Contribution of the B20-B23 beta-turn to activity and stability. J Biol Chem 2006; 281:22386-22396. [PMID: 16751187 DOI: 10.1074/jbc.m603547200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin contains a beta-turn (residues B20-B23) interposed between two receptor-binding elements, the central alpha-helix of the B chain (B9-B19) and its C-terminal beta-strand (B24-B28). The turn contains conserved glycines at B20 and B23. Although insulin exhibits marked conformational variability among crystal forms, these glycines consistently maintain positive phi dihedral angles within a classic type-I beta-turn. Because the Ramachandran conformations of GlyB20 and GlyB23 are ordinarily forbidden to L-amino acids, turn architecture may contribute to structure or function. Here, we employ "chiral mutagenesis," comparison of corresponding D- and L-Ala substitutions, to investigate this turn. Control substitutions are introduced at GluB21, a neighboring residue exhibiting a conventional (negative) phi angle. The D- and L-Ala substitutions at B23 are associated with a marked stereospecific difference in activity. Whereas the D-AlaB23 analog retains native activity, the L analog exhibits a 20-fold decrease in receptor binding. By contrast, D- and L-AlaB20 analogs each exhibit high activity. Stereospecific differences between the thermodynamic stabilities of the analogs are nonetheless more pronounced at B20 (delta deltaG(u) 2.0 kcal/mole) than at B23 (delta deltaG(u) 0.7 kcal/mole). Control substitutions at B21 are well tolerated without significant stereospecificity. Chiral mutagenesis thus defines the complementary contributions of these conserved glycines to protein stability (GlyB20) or receptor recognition (GlyB23).
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Affiliation(s)
- Satoe H Nakagawa
- Department of Biochemistry & Molecular Biology, University of Chicago, Chicago, Illinois 60637
| | - Qing-Xin Hua
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
| | - Shi-Quan Hu
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
| | - Wenhua Jia
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
| | - Shuhua Wang
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
| | - Panayotis G Katsoyannis
- Department of Pharmacology & Biological Chemistry, Mt. Sinai School of Medicine, New York, New York 10029
| | - Michael A Weiss
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106.
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27
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Hua QX, Liu M, Hu SQ, Jia W, Arvan P, Weiss MA. A conserved histidine in insulin is required for the foldability of human proinsulin: structure and function of an ALAB5 analog. J Biol Chem 2006; 281:24889-99. [PMID: 16728398 DOI: 10.1074/jbc.m602617200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The insulins of eutherian mammals contain histidines at positions B5 and B10. The role of His(B10) is well defined: although not required in the mature hormone for receptor binding, in the islet beta cell this side chain functions in targeting proinsulin to glucose-regulated secretory granules and provides axial zincbinding sites in storage hexamers. In contrast, the role of His(B5) is less well understood. Here, we demonstrate that its substitution with Ala markedly impairs insulin chain combination in vitro and blocks the folding and secretion of human proinsulin in a transfected mammalian cell line. The structure and stability of an Ala(B5)-insulin analog were investigated in an engineered monomer (DKP-insulin). Despite its impaired foldability, the structure of the Ala(B5) analog retains a native-like T-state conformation. At the site of substitution, interchain nuclear Overhauser effects are observed between the methyl resonance of Ala(B5) and side chains in the A chain; these nuclear Overhauser effects resemble those characteristic of His(B5) in native insulin. Substantial receptor binding activity is retained (80 +/- 10% relative to the parent monomer). Although the thermodynamic stability of the Ala(B5) analog is decreased (DeltaDeltaG(u) = 1.7 +/- 0.1 kcal/mol), consistent with loss of His(B5)-related interchain packing and hydrogen bonds, control studies suggest that this decrement cannot account for its impaired foldability. We propose that nascent long-range interactions by His(B5) facilitate alignment of Cys(A7) and Cys(B7) in protein-folding intermediates; its conservation thus reflects mechanisms of oxidative folding rather than structure-function relationships in the native state.
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Affiliation(s)
- Qing-Xin Hua
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106-4935
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28
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Zoete V, Meuwly M, Karplus M. Study of the insulin dimerization: binding free energy calculations and per-residue free energy decomposition. Proteins 2006; 61:79-93. [PMID: 16080143 DOI: 10.1002/prot.20528] [Citation(s) in RCA: 185] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A calculation of the binding free energy for the dimerization of insulin has been performed using the molecular mechanics-generalized Born surface area approach. The calculated absolute binding free energy is -11.9 kcal/mol, in approximate agreement with the experimental value of -7.2 kcal/mol. The results show that the dimerization is mainly due to nonpolar interactions. The role of the hydrogen bonds between the 2 monomers appears to give the direction of the interactions. A per-atom decomposition of the binding free energy has been performed to identify the residues contributing most to the self association free energy. Residues B24-B26 are found to make the largest favorable contributions to the dimerization. Other residues situated at the interface between the 2 monomers were found to make favorable but smaller contributions to the dimerization: Tyr B16, Val B12, and Pro B28, and to an even lesser extent, Gly B23. The energy decomposition on a per-residue basis is in agreement with experimental alanine scanning data. The results obtained from a single trajectory (i.e., the dimer trajectory is also used for the monomer analysis) and 2 trajectories (i.e., separate trajectories are used for the monomer and dimer) are similar.
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Affiliation(s)
- Vincent Zoete
- Laboratoire de Chimie Biophysique, ISIS/Université Louis Pasteur, Strasbourg Cedex, France
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Nakagawa SH, Zhao M, Hua QX, Hu SQ, Wan ZL, Jia W, Weiss MA. Chiral mutagenesis of insulin. Foldability and function are inversely regulated by a stereospecific switch in the B chain. Biochemistry 2005; 44:4984-99. [PMID: 15794637 PMCID: PMC3845378 DOI: 10.1021/bi048025o] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
How insulin binds to its receptor is unknown despite decades of investigation. Here, we employ chiral mutagenesis-comparison of corresponding d and l amino acid substitutions in the hormone-to define a structural switch between folding-competent and active conformations. Our strategy is motivated by the T --> R transition, an allosteric feature of zinc-hexamer assembly in which an invariant glycine in the B chain changes conformations. In the classical T state, Gly(B8) lies within a beta-turn and exhibits a positive phi angle (like a d amino acid); in the alternative R state, Gly(B8) is part of an alpha-helix and exhibits a negative phi angle (like an l amino acid). Respective B chain libraries containing mixtures of d or l substitutions at B8 exhibit a stereospecific perturbation of insulin chain combination: l amino acids impede native disulfide pairing, whereas diverse d substitutions are well-tolerated. Strikingly, d substitutions at B8 enhance both synthetic yield and thermodynamic stability but markedly impair biological activity. The NMR structure of such an inactive analogue (as an engineered T-like monomer) is essentially identical to that of native insulin. By contrast, l analogues exhibit impaired folding and stability. Although synthetic yields are very low, such analogues can be highly active. Despite the profound differences between the foldabilities of d and l analogues, crystallization trials suggest that on protein assembly substitutions of either class can be accommodated within classical T or R states. Comparison between such diastereomeric analogues thus implies that the T state represents an inactive but folding-competent conformation. We propose that within folding intermediates the sign of the B8 phi angle exerts kinetic control in a rugged landscape to distinguish between trajectories associated with productive disulfide pairing (positive T-like values) or off-pathway events (negative R-like values). We further propose that the crystallographic T -->R transition in part recapitulates how the conformation of an insulin monomer changes on receptor binding. At the very least the ostensibly unrelated processes of disulfide pairing, allosteric assembly, and receptor binding appear to utilize the same residue as a structural switch; an "ambidextrous" glycine unhindered by the chiral restrictions of the Ramachandran plane. We speculate that this switch operates to protect insulin-and the beta-cell-from protein misfolding.
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Affiliation(s)
- Satoe H. Nakagawa
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637
| | - Ming Zhao
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637
| | - Qing-xin Hua
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106-4935
| | - Shi-Quan Hu
- Department of Pharmacology and Biological Chemistry, Mt. Sinai School of Medicine of New York University, New York, New York 10029
| | - Zhu-li Wan
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106-4935
| | - Wenhua Jia
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106-4935
| | - Michael A. Weiss
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106-4935
- To whom correspondence should be addressed. ; telephone: (216) 368-5991; fax: (216) 368-3419
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Denley A, Wang CC, McNeil KA, Walenkamp MJE, van Duyvenvoorde H, Wit JM, Wallace JC, Norton RS, Karperien M, Forbes BE. Structural and functional characteristics of the Val44Met insulin-like growth factor I missense mutation: correlation with effects on growth and development. Mol Endocrinol 2004; 19:711-21. [PMID: 15576456 DOI: 10.1210/me.2004-0409] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
We have previously described the phenotype resulting from a missense mutation in the IGF-I gene, which leads to expression of IGF-I with a methionine instead of a valine at position 44 (Val44Met IGF-I). This mutation caused severe growth and mental retardation as well as deafness evident at birth and growth retardation in childhood, but is relatively well tolerated in adulthood. We have conducted a biochemical and structural analysis of Val44Met IGF-I to provide a molecular basis for the phenotype observed. Val44Met IGF-I exhibits a 90-fold decrease in type 1 IGF receptor (IGF-1R) binding compared with wild-type human IGF-I and only poorly stimulates autophosphorylation of the IGF-1R. The ability of Val44Met IGF-I to signal via the extracellular signal-regulated kinase 1/2 and Akt/protein kinase B pathways and to stimulate DNA synthesis is correspondingly poorer. Binding or activation of both insulin receptor isoforms is not detectable even at micromolar concentrations. However, Val44Met IGF-I binds IGF-binding protein-2 (IGFBP-2), IGFBP-3, and IGFBP-6 with equal affinity to IGF-I, suggesting the maintenance of overall structure, particularly in the IGFBP binding domain. Structural analysis by nuclear magnetic resonance confirms retention of near-native structure with only local side-chain disruptions despite the significant loss of function. To our knowledge, our results provide the first structural study of a naturally occurring mutant human IGF-I associated with growth and developmental abnormalities and identifies Val44 as an essential residue involved in the IGF-IGF-1R interaction.
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Affiliation(s)
- Adam Denley
- School of Molecular and Biomedical Science, University of Adelaide, Adelaide, 5005 South Australia
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Zoete V, Meuwly M, Karplus M. A Comparison of the Dynamic Behavior of Monomeric and Dimeric Insulin Shows Structural Rearrangements in the Active Monomer. J Mol Biol 2004; 342:913-29. [PMID: 15342246 DOI: 10.1016/j.jmb.2004.07.033] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2004] [Revised: 07/07/2004] [Accepted: 07/07/2004] [Indexed: 10/26/2022]
Abstract
Molecular dynamics (MD) simulations (5-10ns in length) and normal mode analyses were performed for the monomer and dimer of native porcine insulin in aqueous solution; both starting structures were obtained from an insulin hexamer. Several simulations were done to confirm that the results obtained are meaningful. The insulin dimer is very stable during the simulation and remains very close to the starting X-ray structure; the RMS fluctuations calculated from the MD simulation agree with the experimental B-factors. Correlated motions were found within each of the two monomers; they can be explained by persistent non-bonded interactions and disulfide bridges. The correlated motions between residues B24 and B26 of the two monomers are due to non-bonded interactions between the side-chains and backbone atoms. For the isolated monomer in solution, the A chain and the helix of the B chain are found to be stable during 5ns and 10ns MD simulations. However, the N-terminal and the C-terminal parts of the B chain are very flexible. The C-terminal part of the B chain moves away from the X-ray conformation after 0.5-2.5ns and exposes the N-terminal residues of the A chain that are thought to be important for the binding of insulin to its receptor. Our results thus support the hypothesis that, when monomeric insulin is released from the hexamer (or the dimer in our study), the C-terminal end of the monomer (residues B25-B30) is rearranged to allow binding to the insulin receptor. The greater flexibility of the C-terminal part of the beta chain in the B24 (Phe-->Gly) mutant is in accord with the NMR results. The details of the backbone and side-chain motions are presented. The transition between the starting conformation and the more dynamic structure of the monomers is characterized by displacements of the backbone of Phe B25 and Tyr B26; of these, Phe B25 has been implicated in insulin activation.
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Affiliation(s)
- Vincent Zoete
- Laboratoire de Chimie Biophysique, ISIS/Université Louis Pasteur, 8, allée Gaspard Monge, BP 70028, 67083 Strasbourg Cedex, France
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Huang K, Xu B, Hu SQ, Chu YC, Hua QX, Qu Y, Li B, Wang S, Wang RY, Nakagawa SH, Theede AM, Whittaker J, De Meyts P, Katsoyannis PG, Weiss MA. How Insulin Binds: the B-Chain α-Helix Contacts the L1 β-Helix of the Insulin Receptor. J Mol Biol 2004; 341:529-50. [PMID: 15276842 DOI: 10.1016/j.jmb.2004.05.023] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2004] [Revised: 05/11/2004] [Accepted: 05/12/2004] [Indexed: 10/26/2022]
Abstract
Binding of insulin to the insulin receptor plays a central role in the hormonal control of metabolism. Here, we investigate possible contact sites between the receptor and the conserved non-polar surface of the B-chain. Evidence is presented that two contiguous sites in an alpha-helix, Val(B12) and Tyr(B16), contact the receptor. Chemical synthesis is exploited to obtain non-standard substitutions in an engineered monomer (DKP-insulin). Substitution of Tyr(B16) by an isosteric photo-activatable derivative (para-azido-phenylalanine) enables efficient cross-linking to the receptor. Such cross-linking is specific and maps to the L1 beta-helix of the alpha-subunit. Because substitution of Val(B12) by larger side-chains markedly impairs receptor binding, cross-linking studies at B12 were not undertaken. Structure-function relationships are instead probed by side-chains of similar or smaller volume: respective substitution of Val(B12) by alanine, threonine, and alpha-aminobutyric acid leads to activities of 1(+/-0.1)%, 13(+/-6)%, and 14(+/-5)% (relative to DKP-insulin) without disproportionate changes in negative cooperativity. NMR structures are essentially identical with native insulin. The absence of transmitted structural changes suggests that the low activities of B12 analogues reflect local perturbation of a "high-affinity" hormone-receptor contact. By contrast, because position B16 tolerates alanine substitution (relative activity 34(+/-10)%), the contribution of this neighboring interaction is smaller. Together, our results support a model in which the B-chain alpha-helix, functioning as an essential recognition element, docks against the L1 beta-helix of the insulin receptor.
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Affiliation(s)
- Kun Huang
- Department of Biochemistry, Case Western Reserve School of Medicine, Cleveland OH 44106-4935, USA
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Xu B, Hu SQ, Chu YC, Wang S, Wang RY, Nakagawa SH, Katsoyannis PG, Weiss MA. Diabetes-associated mutations in insulin identify invariant receptor contacts. Diabetes 2004; 53:1599-602. [PMID: 15161767 DOI: 10.2337/diabetes.53.6.1599] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Mutations in human insulin cause an autosomal-dominant syndrome of diabetes and fasting hyperinsulinemia. We demonstrate by residue-specific photo cross-linking that diabetes-associated mutations occur at receptor-binding sites. The studies use para-azido-phenylalanine, introduced at five sites by total protein synthesis. Because two such sites (Val(A3) and Phe(B24)) are largely buried in crystal structures of the free hormone, their participation in receptor binding is likely to require a conformational change to expose a hidden functional surface. Our results demonstrate that this surface spans both chains of the insulin molecule and includes sites of rare human mutations that cause diabetes.
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Affiliation(s)
- Bin Xu
- Case Western Reserve University, Department of Biochemistry, 10900 Euclid Ave., SOM Room W427, Cleveland, OH 44106-4935, USA
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Hua QX, Weiss MA. Mechanism of insulin fibrillation: the structure of insulin under amyloidogenic conditions resembles a protein-folding intermediate. J Biol Chem 2004; 279:21449-60. [PMID: 14988398 DOI: 10.1074/jbc.m314141200] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin undergoes aggregation-coupled misfolding to form a cross-beta assembly. Such fibrillation has long complicated its manufacture and use in the therapy of diabetes mellitus. Of interest as a model for disease-associated amyloids, insulin fibrillation is proposed to occur via partial unfolding of a monomeric intermediate. Here, we describe the solution structure of human insulin under amyloidogenic conditions (pH 2.4 and 60 degrees C). Use of an enhanced sensitivity cryogenic probe at high magnetic field avoids onset of fibrillation during spectral acquisition. A novel partial fold is observed in which the N-terminal segments of the A- and B-chains detach from the core. Unfolding of the N-terminal alpha-helix of the A-chain exposes a hydrophobic surface formed by native-like packing of the remaining alpha-helices. The C-terminal segment of the B-chain, although not well ordered, remains tethered to this partial helical core. We propose that detachment of N-terminal segments makes possible aberrant protein-protein interactions in an amyloidogenic nucleus. Non-cooperative unfolding of the N-terminal A-chain alpha-helix resembles that observed in models of proinsulin folding intermediates and foreshadows the extensive alpha --> beta transition characteristic of mature fibrils.
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Affiliation(s)
- Qing-xin Hua
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44016-4935
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Narendra U, Zhu L, Li B, Wilken J, Weiss MA. Sex-specific gene regulation. The Doublesex DM motif is a bipartite DNA-binding domain. J Biol Chem 2002; 277:43463-73. [PMID: 12198117 DOI: 10.1074/jbc.m204616200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sex-specific gene expression in Drosophila melanogaster is regulated in part by the Doublesex (DSX) transcription factor. Male- and female-specific splicing isoforms share a novel DNA-binding domain, designated the DM motif. This domain is conserved among a newly recognized family of vertebrate transcription factors involved in developmental patterning and sex determination. The DM motif consists of an N-terminal zinc module and a disordered C-terminal tail, hypothesized to fold on specific DNA binding as a recognition alpha-helix. Truncation of the tail does not perturb the structure of the zinc module but impairs DNA binding and DNA-dependent dimerization. Chemical protein synthesis and alanine scanning mutagenesis are employed to test the contributions of 13 side chains to specific DNA binding. Selected arginine or lysine residues in the zinc module were substituted by norleucine, an isostere that maintains the aliphatic portion of the side chain but lacks a positive charge. Arginine or glutamine residues in the tail were substituted by alanine. Evidence is obtained that both the zinc module and C-terminal tail contribute to a bipartite DNA-binding surface. Conserved arginine and glutamine residues in the tail are required for high affinity DNA recognition, consistent with its proposed role as a nascent recognition alpha-helix.
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Affiliation(s)
- Uma Narendra
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA
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Hua QX, Chu YC, Jia W, Phillips NFB, Wang RY, Katsoyannis PG, Weiss MA. Mechanism of insulin chain combination. Asymmetric roles of A-chain alpha-helices in disulfide pairing. J Biol Chem 2002; 277:43443-53. [PMID: 12196530 DOI: 10.1074/jbc.m206107200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The A and B chains of insulin combine to form native disulfide bridges without detectable isomers. The fidelity of chain combination thus recapitulates the folding of proinsulin, a precursor protein in which the two chains are tethered by a disordered connecting peptide. We have recently shown that chain combination is blocked by seemingly conservative substitutions in the C-terminal alpha-helix of the A chain. Such analogs, once formed, nevertheless retain high biological activity. By contrast, we demonstrate here that chain combination is robust to non-conservative substitutions in the N-terminal alpha-helix. Introduction of multiple glycine substitutions into the N-terminal segment of the A chain (residues A1-A5) yields analogs that are less stable than native insulin and essentially without biological activity. (1)H NMR studies of a representative analog lacking invariant side chains Ile(A2) and Val(A3) (A chain sequence GGGEQCCTSICSLYQLENYCN; substitutions are italicized and cysteines are underlined) demonstrate local unfolding of the A1-A5 segment in an otherwise native-like structure. That this and related partial folds retain efficient disulfide pairing suggests that the native N-terminal alpha-helix does not participate in the transition state of the reaction. Implications for the hierarchical folding mechanisms of proinsulin and insulin-like growth factors are discussed.
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Affiliation(s)
- Qing-Xin Hua
- Department of Biochemistry, Case Western Reserve School of Medicine, Cleveland, Ohio 44106-4935, USA
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