1
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Smith NA, Menting JG, Weiss MA, Lawrence MC, Smith BJ. Single-chain insulin analogs threaded by the insulin receptor αCT domain. Biophys J 2022; 121:4063-4077. [PMID: 36181268 PMCID: PMC9675026 DOI: 10.1016/j.bpj.2022.09.038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Revised: 09/12/2022] [Accepted: 09/28/2022] [Indexed: 11/18/2022] Open
Abstract
Insulin is a mainstay of therapy for diabetes mellitus, yet its thermal stability complicates global transportation and storage. Cold-chain transport, coupled with optimized formulation and materials, prevents to some degree nucleation of amyloid and hence inactivation of hormonal activity. These issues hence motivate the design of analogs with increased stability, with a promising approach being single-chain insulins (SCIs), whose C domains (foreshortened relative to proinsulin) resemble those of the single-chain growth factors (IGFs). We have previously demonstrated that optimized SCIs can exhibit native-like hormonal activity with enhanced thermal stability and marked resistance to fibrillation. Here, we describe the crystal structure of an ultrastable SCI (C-domain length 6; sequence EEGPRR) bound to modules of the insulin receptor (IR) ectodomain (N-terminal α-subunit domains L1-CR and C-terminal αCT peptide; "microreceptor" [μIR]). The structure of the SCI-μIR complex, stabilized by an Fv module, was determined using diffraction data to a resolution of 2.6 Å. Remarkably, the αCT peptide (IR-A isoform) "threads" through a gap between the flexible C domain and the insulin core. To explore such threading, we undertook molecular dynamics simulations to 1) compare threaded with unthreaded binding modes and 2) evaluate effects of C-domain length on these alternate modes. The simulations (employing both conventional and enhanced sampling simulations) provide evidence that very short linkers (C-domain length of -1) would limit gap opening in the SCI and so impair threading. We envisage that analogous threading occurs in the intact SCI-IR complex-rationalizing why minimal C-domain lengths block complete activity-and might be exploited to design novel receptor-isoform-specific analogs.
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Affiliation(s)
- Nicholas A Smith
- La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, Australia
| | - John G Menting
- WEHI, Parkville, Victoria, Australia; Department of Medical Biology, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville, Victoria, Australia
| | - Michael A Weiss
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana.
| | - Michael C Lawrence
- WEHI, Parkville, Victoria, Australia; Department of Medical Biology, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville, Victoria, Australia.
| | - Brian J Smith
- La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, Australia.
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2
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Chen YS, Gleaton J, Yang Y, Dhayalan B, Phillips NB, Liu Y, Broadwater L, Jarosinski MA, Chatterjee D, Lawrence MC, Hattier T, Michael MD, Weiss MA. Insertion of a synthetic switch into insulin provides metabolite-dependent regulation of hormone-receptor activation. Proc Natl Acad Sci U S A 2021; 118:e2103518118. [PMID: 34290145 PMCID: PMC8325334 DOI: 10.1073/pnas.2103518118] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Insulin-signaling requires conformational change: whereas the free hormone and its receptor each adopt autoinhibited conformations, their binding leads to structural reorganization. To test the functional coupling between insulin's "hinge opening" and receptor activation, we inserted an artificial ligand-dependent switch into the insulin molecule. Ligand-binding disrupts an internal tether designed to stabilize the hormone's native closed and inactive conformation, thereby enabling productive receptor engagement. This scheme exploited a diol sensor (meta-fluoro-phenylboronic acid at GlyA1) and internal diol (3,4-dihydroxybenzoate at LysB28). The sensor recognizes monosaccharides (fructose > glucose). Studies of insulin-signaling in human hepatoma-derived cells (HepG2) demonstrated fructose-dependent receptor autophosphorylation leading to appropriate downstream signaling events, including a specific kinase cascade and metabolic gene regulation (gluconeogenesis and lipogenesis). Addition of glucose (an isomeric ligand with negligible sensor affinity) did not activate the hormone. Similarly, metabolite-regulated signaling was not observed in control studies of 1) an unmodified insulin analog or 2) an analog containing a diol sensor without internal tethering. Although secondary structure (as probed by circular dichroism) was unaffected by ligand-binding, heteronuclear NMR studies revealed subtle local and nonlocal monosaccharide-dependent changes in structure. Insertion of a synthetic switch into insulin has thus demonstrated coupling between hinge-opening and allosteric holoreceptor signaling. In addition to this foundational finding, our results provide proof of principle for design of a mechanism-based metabolite-responsive insulin. In particular, replacement of the present fructose sensor by an analogous glucose sensor may enable translational development of a "smart" insulin analog to mitigate hypoglycemic risk in diabetes therapy.
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Affiliation(s)
- Yen-Shan Chen
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202
| | | | - Yanwu Yang
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202
| | - Balamurugan Dhayalan
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202
| | - Nelson B Phillips
- Department of Biochemistry, Case Western Reserve University, Cleveland, OH 44106
| | - Yule Liu
- Thermalin Inc., Cleveland, OH 44106
| | | | - Mark A Jarosinski
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202
| | - Deepak Chatterjee
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202
| | - Michael C Lawrence
- Structural Biology Division, WEHI, Parkville, VIC 3052, Australia
- Department of Medical Biology, University of Melbourne, Royal Parade, Parkville, VIC 3050, Australia
| | | | | | - Michael A Weiss
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202;
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3
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Rege NK, Liu M, Dhayalan B, Chen YS, Smith NA, Rahimi L, Sun J, Guo H, Yang Y, Haataja L, Phillips NFB, Whittaker J, Smith BJ, Arvan P, Ismail-Beigi F, Weiss MA. "Register-shift" insulin analogs uncover constraints of proteotoxicity in protein evolution. J Biol Chem 2020; 295:3080-3098. [PMID: 32005662 DOI: 10.1074/jbc.ra119.011389] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Revised: 01/27/2020] [Indexed: 12/16/2022] Open
Abstract
Globular protein sequences encode not only functional structures (the native state) but also protein foldability, i.e. a conformational search that is both efficient and robustly minimizes misfolding. Studies of mutations associated with toxic misfolding have yielded insights into molecular determinants of protein foldability. Of particular interest are residues that are conserved yet dispensable in the native state. Here, we exploited the mutant proinsulin syndrome (a major cause of permanent neonatal-onset diabetes mellitus) to investigate whether toxic misfolding poses an evolutionary constraint. Our experiments focused on an invariant aromatic motif (PheB24-PheB25-TyrB26) with complementary roles in native self-assembly and receptor binding. A novel class of mutations provided evidence that insulin can bind to the insulin receptor (IR) in two different modes, distinguished by a "register shift" in this motif, as visualized by molecular dynamics (MD) simulations. Register-shift variants are active but defective in cellular foldability and exquisitely susceptible to fibrillation in vitro Indeed, expression of the corresponding proinsulin variant induced endoplasmic reticulum stress, a general feature of the mutant proinsulin syndrome. Although not present among vertebrate insulin and insulin-like sequences, a prototypical variant ([GlyB24]insulin) was as potent as WT insulin in a rat model of diabetes. Although in MD simulations the shifted register of receptor engagement is compatible with the structure and allosteric reorganization of the IR-signaling complex, our results suggest that this binding mode is associated with toxic misfolding and so is disallowed in evolution. The implicit threat of proteotoxicity limits sequence variation among vertebrate insulins and insulin-like growth factors.
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Affiliation(s)
- Nischay K Rege
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Ming Liu
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan 48105, Australia; Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin, Heping District, 300052 China
| | - Balamurugan Dhayalan
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202
| | - Yen-Shan Chen
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202
| | - Nicholas A Smith
- La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Leili Rahimi
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106; Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Jinhong Sun
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan 48105, Australia
| | - Huan Guo
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan 48105, Australia
| | - Yanwu Yang
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202
| | - Leena Haataja
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan 48105, Australia
| | - Nelson F B Phillips
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Jonathan Whittaker
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Brian J Smith
- La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Peter Arvan
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan 48105, Australia
| | - Faramarz Ismail-Beigi
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106; Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Michael A Weiss
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202.
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4
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Mao R, Chen Y, Chi Z, Wang Y. Insulin and its single-chain analogue. Appl Microbiol Biotechnol 2019; 103:8737-8751. [DOI: 10.1007/s00253-019-10170-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2019] [Revised: 10/02/2019] [Accepted: 10/08/2019] [Indexed: 12/26/2022]
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5
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Glucose-responsive insulin by molecular and physical design. Nat Chem 2019; 9:937-943. [PMID: 28937662 DOI: 10.1038/nchem.2857] [Citation(s) in RCA: 89] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 07/11/2017] [Indexed: 12/15/2022]
Abstract
The concept of a glucose-responsive insulin (GRI) has been a recent objective of diabetes technology. The idea behind the GRI is to create a therapeutic that modulates its potency, concentration or dosing relative to a patient's dynamic glucose concentration, thereby approximating aspects of a normally functioning pancreas. From the perspective of the medicinal chemist, the GRI is also important as a generalized model of a potentially new generation of therapeutics that adjust potency in response to a critical therapeutic marker. The aim of this Perspective is to highlight emerging concepts, including mathematical modelling and the molecular engineering of insulin itself and its potency, towards a viable GRI. We briefly outline some of the most important recent progress toward this goal and also provide a forward-looking viewpoint, which asks if there are new approaches that could spur innovation in this area as well as to encourage synthetic chemists and chemical engineers to address the challenges and promises offered by this therapeutic approach.
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6
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Glidden MD, Aldabbagh K, Phillips NB, Carr K, Chen YS, Whittaker J, Phillips M, Wickramasinghe NP, Rege N, Swain M, Peng Y, Yang Y, Lawrence MC, Yee VC, Ismail-Beigi F, Weiss MA. An ultra-stable single-chain insulin analog resists thermal inactivation and exhibits biological signaling duration equivalent to the native protein. J Biol Chem 2017; 293:47-68. [PMID: 29114035 DOI: 10.1074/jbc.m117.808626] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Revised: 10/12/2017] [Indexed: 12/12/2022] Open
Abstract
Thermal degradation of insulin complicates its delivery and use. Previous efforts to engineer ultra-stable analogs were confounded by prolonged cellular signaling in vivo, of unclear safety and complicating mealtime therapy. We therefore sought an ultra-stable analog whose potency and duration of action on intravenous bolus injection in diabetic rats are indistinguishable from wild-type (WT) insulin. Here, we describe the structure, function, and stability of such an analog, a 57-residue single-chain insulin (SCI) with multiple acidic substitutions. Cell-based studies revealed native-like signaling properties with negligible mitogenic activity. Its crystal structure, determined as a novel zinc-free hexamer at 2.8 Å, revealed a native insulin fold with incomplete or absent electron density in the C domain; complementary NMR studies are described in the accompanying article. The stability of the analog (ΔGU 5.0(±0.1) kcal/mol at 25 °C) was greater than that of WT insulin (3.3(±0.1) kcal/mol). On gentle agitation, the SCI retained full activity for >140 days at 45 °C and >48 h at 75 °C. These findings indicate that marked resistance to thermal inactivation in vitro is compatible with native duration of activity in vivo Further, whereas WT insulin forms large and heterogeneous aggregates above the standard 0.6 mm pharmaceutical strength, perturbing the pharmacokinetic properties of concentrated formulations, dynamic light scattering, and size-exclusion chromatography revealed only limited SCI self-assembly and aggregation in the concentration range 1-7 mm Such a combination of favorable biophysical and biological properties suggests that SCIs could provide a global therapeutic platform without a cold chain.
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Affiliation(s)
- Michael D Glidden
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106; Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106
| | - Khadijah Aldabbagh
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Nelson B Phillips
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Kelley Carr
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Yen-Shan Chen
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Jonathan Whittaker
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Manijeh Phillips
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | | | - Nischay Rege
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Mamuni Swain
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Yi Peng
- Department of Nutrition, Case Western Reserve University, Cleveland, Ohio 44106
| | - Yanwu Yang
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - 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
| | - Vivien C Yee
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106
| | - Faramarz Ismail-Beigi
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106; Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106; Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Michael A Weiss
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106; Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44106; Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106.
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7
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Avital-Shmilovici M, Mandal K, Gates ZP, Phillips NB, Weiss MA, Kent SBH. Fully convergent chemical synthesis of ester insulin: determination of the high resolution X-ray structure by racemic protein crystallography. J Am Chem Soc 2013; 135:3173-85. [PMID: 23343390 DOI: 10.1021/ja311408y] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Efficient total synthesis of insulin is important to enable the application of medicinal chemistry to the optimization of the properties of this important protein molecule. Recently we described "ester insulin"--a novel form of insulin in which the function of the 35 residue C-peptide of proinsulin is replaced by a single covalent bond--as a key intermediate for the efficient total synthesis of insulin. Here we describe a fully convergent synthetic route to the ester insulin molecule from three unprotected peptide segments of approximately equal size. The synthetic ester insulin polypeptide chain folded much more rapidly than proinsulin, and at physiological pH. Both the D-protein and L-protein enantiomers of monomeric DKP ester insulin (i.e., [Asp(B10), Lys(B28), Pro(B29)]ester insulin) were prepared by total chemical synthesis. The atomic structure of the synthetic ester insulin molecule was determined by racemic protein X-ray crystallography to a resolution of 1.6 Å. Diffraction quality crystals were readily obtained from the racemic mixture of {D-DKP ester insulin + L-DKP ester insulin}, whereas crystals were not obtained from the L-ester insulin alone even after extensive trials. Both the D-protein and L-protein enantiomers of monomeric DKP ester insulin were assayed for receptor binding and in diabetic rats, before and after conversion by saponification to the corresponding DKP insulin enantiomers. L-DKP ester insulin bound weakly to the insulin receptor, while synthetic L-DKP insulin derived from the L-DKP ester insulin intermediate was fully active in binding to the insulin receptor. The D- and L-DKP ester insulins and D-DKP insulin were inactive in lowering blood glucose in diabetic rats, while synthetic L-DKP insulin was fully active in this biological assay. The structural basis of the lack of biological activity of ester insulin is discussed.
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8
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Pedersen SL, Tofteng AP, Malik L, Jensen KJ. Microwave heating in solid-phase peptide synthesis. Chem Soc Rev 2012; 41:1826-44. [DOI: 10.1039/c1cs15214a] [Citation(s) in RCA: 214] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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9
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Kiselar JG, Datt M, Chance MR, Weiss MA. Structural analysis of proinsulin hexamer assembly by hydroxyl radical footprinting and computational modeling. J Biol Chem 2011; 286:43710-43716. [PMID: 22033917 DOI: 10.1074/jbc.m111.297853] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in the insulin gene can impair proinsulin folding and cause diabetes mellitus. Although crystal structures of insulin dimers and hexamers are well established, proinsulin is refractory to crystallization. Although an NMR structure of an engineered proinsulin monomer has been reported, structures of the wild-type monomer and hexamer remain undetermined. We have utilized hydroxyl radical footprinting and molecular modeling to characterize these structures. Differences between the footprints of insulin and proinsulin, defining a "shadow" of the connecting (C) domain, were employed to refine the model. Our results demonstrate that in its monomeric form, (i) proinsulin contains a native-like insulin moiety and (ii) the C-domain footprint resides within an adjoining segment (residues B23-B29) that is accessible to modification in insulin but not proinsulin. Corresponding oxidation rates were observed within core insulin moieties of insulin and proinsulin hexamers, suggesting that the proinsulin hexamer retains an A/B structure similar to that of insulin. Further similarities in rates of oxidation between the respective C-domains of proinsulin monomers and hexamers suggest that this loop in each case flexibly projects from an outer surface. Although dimerization or hexamer assembly would not be impaired, an ensemble of predicted C-domain positions would block hexamer-hexamer stacking as visualized in classical crystal lattices. We anticipate that protein footprinting in combination with modeling, as illustrated here, will enable comparative studies of diabetes-associated mutant proinsulins and their aberrant modes of aggregation.
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Affiliation(s)
- Janna G Kiselar
- Center for Proteomics and Bioinformatics, Case Western Reserve University, Cleveland, Ohio 44106.
| | - Manish Datt
- Center for Proteomics and Bioinformatics, Case Western Reserve University, Cleveland, Ohio 44106
| | - Mark R Chance
- Center for Proteomics and Bioinformatics, Case Western Reserve University, Cleveland, Ohio 44106; Center for Synchrotron Biosciences, Case Western Reserve University, Cleveland, Ohio 44106
| | - Michael A Weiss
- Departments of Biochemistry and Medicine, Case Western Reserve University, Cleveland, Ohio 44106
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10
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Sohma Y, Hua QX, Whittaker J, Weiss MA, Kent SBH. Design and folding of [GluA4(ObetaThrB30)]insulin ("ester insulin"): a minimal proinsulin surrogate that can be chemically converted into human insulin. Angew Chem Int Ed Engl 2011; 49:5489-93. [PMID: 20509131 DOI: 10.1002/anie.201001151] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Youhei Sohma
- Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637, USA.
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11
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Abstract
We have exploited a prandial insulin analog to elucidate the underlying structure and dynamics of insulin as a monomer in solution. A model was provided by insulin lispro (the active component of Humalog(®); Eli Lilly and Co.). Whereas NMR-based modeling recapitulated structural relationships of insulin crystals (T-state protomers), dynamic anomalies were revealed by amide-proton exchange kinetics in D(2)O. Surprisingly, the majority of hydrogen bonds observed in crystal structures are only transiently maintained in solution, including key T-state-specific inter-chain contacts. Long-lived hydrogen bonds (as defined by global exchange kinetics) exist only at a subset of four α-helical sites (two per chain) flanking an internal disulfide bridge (cystine A20-B19); these sites map within the proposed folding nucleus of proinsulin. The anomalous flexibility of insulin otherwise spans its active surface and may facilitate receptor binding. Because conformational fluctuations promote the degradation of pharmaceutical formulations, we envisage that "dynamic re-engineering" of insulin may enable design of ultra-stable formulations for humanitarian use in the developing world.
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Affiliation(s)
- Qing-Xin Hua
- Department of Biochemistry, School of Medicine, Case Western Reserve UniversityCleveland, OH, USA
| | - Wenhua Jia
- Department of Biochemistry, School of Medicine, Case Western Reserve UniversityCleveland, OH, USA
| | - Michael A. Weiss
- Department of Biochemistry, School of Medicine, Case Western Reserve UniversityCleveland, OH, USA
- *Correspondence: Michael A. Weiss, Department of Biochemistry, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue – Wood W436, Cleveland, OH 44106-4935, USA. e-mail:
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12
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Sohma Y, Hua QX, Whittaker J, Weiss M, Kent S. Design and Folding of [GluA4(OβThrB30)]Insulin (“Ester Insulin”): A Minimal Proinsulin Surrogate that Can Be Chemically Converted into Human Insulin. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201001151] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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13
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Kolychev AP. Structural organization of binding determinants in the molecule of insulin-like growth factor-I (IGF-I). J EVOL BIOCHEM PHYS+ 2010. [DOI: 10.1134/s002209301001010x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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14
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Yang Y, Petkova A, Huang K, Xu B, Hua QX, Ye IJ, Chu YC, Hu SQ, Phillips NB, Whittaker J, Ismail-Beigi F, Mackin RB, Katsoyannis PG, Tycko R, Weiss MA. An Achilles' heel in an amyloidogenic protein and its repair: insulin fibrillation and therapeutic design. J Biol Chem 2010; 285:10806-21. [PMID: 20106984 PMCID: PMC2856287 DOI: 10.1074/jbc.m109.067850] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2009] [Revised: 01/19/2010] [Indexed: 11/06/2022] Open
Abstract
Insulin fibrillation provides a model for a broad class of amyloidogenic diseases. Conformational distortion of the native monomer leads to aggregation-coupled misfolding. Whereas beta-cells are protected from proteotoxicity by hexamer assembly, fibrillation limits the storage and use of insulin at elevated temperatures. Here, we have investigated conformational distortions of an engineered insulin monomer in relation to the structure of an insulin fibril. Anomalous (13)C NMR chemical shifts and rapid (15)N-detected (1)H-(2)H amide-proton exchange were observed in one of the three classical alpha-helices (residues A1-A8) of the hormone, suggesting a conformational equilibrium between locally folded and unfolded A-chain segments. Whereas hexamer assembly resolves these anomalies in accordance with its protective role, solid-state (13)C NMR studies suggest that the A-chain segment participates in a fibril-specific beta-sheet. Accordingly, we investigated whether helicogenic substitutions in the A1-A8 segment might delay fibrillation. Simultaneous substitution of three beta-branched residues (Ile(A2) --> Leu, Val(A3) --> Leu, and Thr(A8) --> His) yielded an analog with reduced thermodynamic stability but marked resistance to fibrillation. Whereas amide-proton exchange in the A1-A8 segment remained rapid, (13)Calpha chemical shifts exhibited a more helical pattern. This analog is essentially without activity, however, as Ile(A2) and Val(A3) define conserved receptor contacts. To obtain active analogs, substitutions were restricted to A8. These analogs exhibit high receptor-binding affinity; representative potency in a rodent model of diabetes mellitus was similar to wild-type insulin. Although (13)Calpha chemical shifts remain anomalous, significant protection from fibrillation is retained. Together, our studies define an "Achilles' heel" in a globular protein whose repair may enhance the stability of pharmaceutical formulations and broaden their therapeutic deployment in the developing world.
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Affiliation(s)
- Yanwu Yang
- From the Departments of Biochemistry and
| | - Aneta Petkova
- the Laboratory of Chemical Physics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0520
| | - Kun Huang
- From the Departments of Biochemistry and
| | - Bin Xu
- From the Departments of Biochemistry and
| | | | - I-Ju Ye
- From the Departments of Biochemistry and
| | - Ying-Chi Chu
- the Department of Pharmacology and Biological Chemistry, Mt. Sinai School of Medicine, New York University, New York, New York 10029, and
| | | | | | | | | | - Robert B. Mackin
- the Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178
| | - Panayotis G. Katsoyannis
- the Department of Pharmacology and Biological Chemistry, Mt. Sinai School of Medicine, New York University, New York, New York 10029, and
| | - Robert Tycko
- the Laboratory of Chemical Physics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0520
| | - Michael A. Weiss
- From the Departments of Biochemistry and
- Medicine, Case Western Reserve University, Cleveland, Ohio 44106
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15
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Sohma Y, Hua QX, Liu M, Phillips NB, Hu SQ, Whittaker J, Whittaker LJ, Ng A, Roberts CT, Arvan P, Kent SBH, Weiss MA. Contribution of residue B5 to the folding and function of insulin and IGF-I: constraints and fine-tuning in the evolution of a protein family. J Biol Chem 2009; 285:5040-55. [PMID: 19959476 DOI: 10.1074/jbc.m109.062992] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proinsulin exhibits a single structure, whereas insulin-like growth factors refold as two disulfide isomers in equilibrium. Native insulin-related growth factor (IGF)-I has canonical cystines (A6-A11, A7-B7, and A20-B19) maintained by IGF-binding proteins; IGF-swap has alternative pairing (A7-A11, A6-B7, and A20-B19) and impaired activity. Studies of mini-domain models suggest that residue B5 (His in insulin and Thr in IGFs) governs the ambiguity or uniqueness of disulfide pairing. Residue B5, a site of mutation in proinsulin causing neonatal diabetes, is thus of broad biophysical interest. Here, we characterize reciprocal B5 substitutions in the two proteins. In insulin, His(B5) --> Thr markedly destabilizes the hormone (DeltaDeltaG(u) 2.0 +/- 0.2 kcal/mol), impairs chain combination, and blocks cellular secretion of proinsulin. The reciprocal IGF-I substitution Thr(B5) --> His (residue 4) specifies a unique structure with native (1)H NMR signature. Chemical shifts and nuclear Overhauser effects are similar to those of native IGF-I. Whereas wild-type IGF-I undergoes thiol-catalyzed disulfide exchange to yield IGF-swap, His(B5)-IGF-I retains canonical pairing. Chemical denaturation studies indicate that His(B5) does not significantly enhance thermodynamic stability (DeltaDeltaG(u) 0.2 +/- 0.2 kcal/mol), implying that the substitution favors canonical pairing by destabilizing competing folds. Whereas the activity of Thr(B5)-insulin is decreased 5-fold, His(B5)-IGF-I exhibits 2-fold increased affinity for the IGF receptor and augmented post-receptor signaling. We propose that conservation of Thr(B5) in IGF-I, rescued from structural ambiguity by IGF-binding proteins, reflects fine-tuning of signal transduction. In contrast, the conservation of His(B5) in insulin highlights its critical role in insulin biosynthesis.
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Affiliation(s)
- Youhei Sohma
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, USA
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16
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Abstract
Acute insulin secretion from stimulated pancreatic beta-cells is derived from the intracellular pool of insulin secretory granules wherein insulin is packaged in a highly concentrated (and in some species, crystalline) state. Here we review experimental work, principally from our laboratory, on the question of biogenesis of mature secretory granules within the broader context of intracellular protein trafficking. Events occurring in the lumen of organelles at various stages of intracellular transport within the secretory pathway and events at the limiting membrane of newly forming secretory granules each contribute to formation of the insulin storage compartment comprising the readily releasable pool.
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Affiliation(s)
- Peter Arvan
- Divisions of Metabolism, Endocrinology, and Diabetes, University of Michigan, Ann Arbor, MI, USA.
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17
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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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18
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Tofteng AP, Jensen KJ, Schäffer L, Hoeg-Jensen T. Total synthesis of desB30 insulin analogues by biomimetic folding of single-chain precursors. Chembiochem 2009; 9:2989-96. [PMID: 19035371 DOI: 10.1002/cbic.200800430] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Insulin is a peptide hormone consisting of 51 amino acids in two chains with three disulfide bridges. Human insulin and various analogues are used for the treatment of diabetes and are produced recombinantly at ton scale. Herein, we report the chemical synthesis of insulin by the step-wise, Fmoc-based, solid-phase synthesis of single-chain precursors with solubilising extensions, which under redox conditions, spontaneously fold with the correct pairing of the three disulfide bridges. The folded, single-chain, insulin precursors can be transformed into bioactive two-chain desB30 insulin by the simultaneous removal of the solubilising extension (4-5 residues) and the chain-bridging C-peptide (3-5 residues) by employing Achromobacter lyticus protease--a process well-known from the yeast-based recombinant production of insulin. The overall yields of synthetic insulins were as much as 6 %, and the synthetic process was straightforward and not labour intensive.
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Affiliation(s)
- A Pernille Tofteng
- Faculty of Life Sciences, University of Copenhagen, Frederiksberg, Denmark
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19
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Abbas A, Grant PJ, Kearney MT. Role of IGF-1 in glucose regulation and cardiovascular disease. Expert Rev Cardiovasc Ther 2008; 6:1135-49. [PMID: 18793116 DOI: 10.1586/14779072.6.8.1135] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
IGF-1 is a peptide hormone that is expressed in most tissues. It shares significant structural and functional similarities with insulin, and is implicated in the pathogenesis of insulin resistance and cardiovascular disease. Recombinant human IGF-1 has been used in Type 2 diabetes to improve insulin sensitivity and aid glycemic control. There is evidence supporting IGF-1 as a vascular protective factor and it may also be beneficial in the treatment of chronic heart failure. Further understanding of the effects of IGF-1 signaling in health and disease may lead to novel approaches to the prevention and treatment of diabetes and cardiovascular disease.
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Affiliation(s)
- Afroze Abbas
- BHF Clinical Research Fellow, Division of Cardiovascular and Diabetes Research, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds, UK.
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20
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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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21
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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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22
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Clemmons DR. Modifying IGF1 activity: an approach to treat endocrine disorders, atherosclerosis and cancer. Nat Rev Drug Discov 2007; 6:821-33. [PMID: 17906644 DOI: 10.1038/nrd2359] [Citation(s) in RCA: 249] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Insulin-like growth factor 1 (IGF1) is a polypeptide hormone that has a high degree of structural similarity to human proinsulin. Owing to its ubiquitous nature and its role in promoting cell growth, strategies to inhibit IGF1 actions are being pursued as potential adjunctive measures for treating diseases such as short stature, atherosclerosis and diabetes. In addition, most tumour cell types possess IGF1 receptors and conditions in the tumour microenvironment, such as hypoxia, can lead to enhanced responsiveness to IGF1. Therefore, inhibiting IGF1 action has been proposed as a specific mechanism for potentiating the effects of existing anticancer therapies or for directly inhibiting tumour cell growth.
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Affiliation(s)
- David R Clemmons
- Division of Endocrinology, Department of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7170, 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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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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25
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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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26
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Huang K, Dong J, Phillips NB, Carey PR, Weiss MA. Proinsulin Is Refractory to Protein Fibrillation. J Biol Chem 2005; 280:42345-55. [PMID: 16239223 DOI: 10.1074/jbc.m507110200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin is susceptible to fibrillation, a misfolding process leading to well ordered cross-beta assembly. Protection from fibrillation in beta cells is provided by sequestration of the susceptible monomer within zinc hexamers. We demonstrate that proinsulin is refractory to fibrillation under conditions that promote the rapid fibrillation of zinc-free insulin. Proinsulin fibrils, as probed by Raman microscopy, are nonetheless similar in structure to insulin fibrils. The connecting peptide, although not well ordered in native proinsulin, participates in a fibril-specific beta-sheet. Native insulin and proinsulin exhibit similar free energies of unfolding as inferred from guanidine denaturation studies: relative amyloidogenicities are thus not correlated with global stability. Strikingly, the susceptibility of proinsulin to fibrillation is increased by scission of the connecting peptide at single sites. We thus propose that the connecting peptide constrains a large scale conformational change in the misfolded protein. A tethering mechanism is proposed based on a model of an insulin protofilament derived from electron-microscopic image reconstruction. The proposed relationship between cross-beta assembly and protein topology is supported by studies of single-chain analogs (mini-proinsulin and insulin-like growth factor I) in which foreshortened connecting peptides further retard fibrillation. In addition to its classic function to facilitate disulfide pairing, the connecting peptide may protect beta cells from toxic protein misfolding in the endoplasmic reticulum.
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Affiliation(s)
- Kun Huang
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA
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27
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Guo ZY, Zhang Z, Jia XY, Tang YH, Feng YM. Mutational analysis of the absolutely conserved B8Gly: consequence on foldability and activity of insulin. Acta Biochim Biophys Sin (Shanghai) 2005; 37:673-9. [PMID: 16215634 DOI: 10.1111/j.1745-7270.2005.00093.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
B8Gly is absolutely conserved in insulins during evolution. Moreover, its corresponding position is always occupied by a Gly residue in other members of insulin superfamily. Previous work showed that Ala replacement of B8Gly significantly decreased both the activity and the foldability of insulin. However, the effects of substitution are complicated, and different replacements sometimes cause significantly different results. To analyze the effects of B8 replacement by different amino acids, three new insulin/single-chain insulin mutants with B8Gly replaced by Ser, Thr or Leu were prepared by protein engineering, and both their foldability and activity were analyzed. In general, replacement of B8Gly by other amino acids causes significant detriment to the foldability of single-chain insulin: the conformations of the three B8 mutants are essentially different from that of wild-type molecules as revealed by circular dichroism; their disulfide stabilities in redox buffer are significantly decreased; their in vitro refolding efficiencies are decreased approximately two folds; the structural stabilities of the mutants with Ser or Thr substitution are decreased significantly, while Leu substitution has little effect as measured by equilibrium guanidine denaturation. As far as biological activity is concerned, Ser replacement of B8Gly has only a moderate effect: its insulin receptor-binding activity is 23% of native insulin. But Thr or Leu replacement produces significant detriment: the receptor-binding potencies of the two mutants are less than 0.2% of native insulin. The present results suggest that Gly is likely the only applicable natural amino acid for the B8 position of insulin where both foldability and activity are concerned.
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Affiliation(s)
- Zhan-Yun Guo
- Key Laboratory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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28
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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: 55] [Impact Index Per Article: 2.9] [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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29
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Guo ZY, Jia XY, Feng YM. Replacement of the interchain disulfide bridge-forming amino acids A7 and B7 by glutamate impairs the structure and activity of insulin. Biol Chem 2004; 385:1171-5. [PMID: 15653430 DOI: 10.1515/bc.2004.151] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Insulin contains three disulfide bonds, one intrachain bond, A6–A11, and two interchain bonds, A7–B7 and A20–B19. Site-directed mutagenesis results (the two cysteine residues of disulfide A7–B7 were replaced by serine) showed that disulfide A7–B7 is crucial to both the structure and activity of insulin. However, chemical modification results showed that the insulin analogs still retained relatively high biological activity when A7Cys and B7Cys were modified by chemical groups with a negative charge. Did the negative charge of the modification groups restore the loss of activity and/or the disturbance of structure of these insulin analogs caused by deletion of disulfide A7–B7? To answer this question, an insulin analog with both A7Cys and B7Cys replaced by Glu, which has a long side-chain and a negative charge, was prepared by protein engineering, and its structure and activity were analyzed. Both the structure and activity of the present analog are very similar to that of the mutant with disulfide A7–B7 replaced by Ser, but significantly different from that of wild-type insulin. The present results suggest that removal of disulfide A7–B7 will result in serious loss of biological activity and the native conformation of insulin, even if the disulfide is replaced by residues with a negative charge.
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Affiliation(s)
- Zhan-Yun Guo
- Key Laboratory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, The Chinese Academy of Sciences, Shanghai 200031, PR China
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30
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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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31
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Jia XY, Guo ZY, Wang Y, Xu Y, Duan SS, Feng YM. Peptide models of four possible insulin folding intermediates with two disulfides. Protein Sci 2004; 12:2412-9. [PMID: 14573855 PMCID: PMC2366966 DOI: 10.1110/ps.0389303] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The single-chain insulin (PIP) can spontaneously fold into native structure through preferred kinetic intermediates. During refolding, pairing of the first disulfide A20-B19 is highly specific, whereas pairing of the second disulfide is likely random because two two-disulfide intermediates have been trapped. To get more details of pairing property of the second disulfide, four model peptides of possible folding intermediates with two disulfides were prepared by protein engineering, and their properties were analyzed. The four model peptides were named [A20-B19, A7-B7]PIP, [A20-B19, A6-B7]PIP, [A20-B19, A6-A11]PIP, and [A20-B19, A7-A11]PIP according to their remaining disulfides. The four model peptides all adopt partially folded structure with moderate conformational differences. In redox buffer, the disulfides of the model peptides are more easily reduced than those of the wild-type PIP. During in vitro refolding, the reduced model peptides share similar relative folding rates but different folding yields: The refolding efficiency of the reduced [A20-B19, A7-A11]PIP is about threefold lower than that of the other three peptides. The present results indicate that the folding intermediates corresponding to the present model peptides all adopt partially folded conformation, and can be formed during PIP refolding, but the chance of forming the intermediate with disulfide [A20-B19, A7-A11] is much lower than that of forming the other three intermediates.
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Affiliation(s)
- Xiao-Yuan Jia
- Key Laboratory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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32
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Arvan P. Secretory protein trafficking. Cell Biochem Biophys 2004. [DOI: 10.1007/bf02739021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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33
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Nguyen MT, Beck J, Lue H, Fünfzig H, Kleemann R, Koolwijk P, Kapurniotu A, Bernhagen J. A 16-residue peptide fragment of macrophage migration inhibitory factor, MIF-(50-65), exhibits redox activity and has MIF-like biological functions. J Biol Chem 2003; 278:33654-71. [PMID: 12796500 DOI: 10.1074/jbc.m301735200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Macrophage migration inhibitory factor (MIF) is a cytokine that participates in the host inflammatory response. A Cys-Xaa-Xaa-Cys (CXXC)-based thiol-protein oxidoreductase activity of MIF is associated with certain biological functions. Peptides spanning the CXXC region of thiol-protein oxidoreductases retain some biochemical properties of the full-length protein. We report on the characterization of CXXC-spanning MIF-(50-65) and its serine variant, C57S/C60S-MIF-(50-65). Following disulfide-mediated cyclization, MIF-(50-65) adapted a beta-turn conformation comparable with that of beta-turn-containing cyclo-57,60-[Asp57,Dap60]MIF-(50-65). MIF-(50-65) had a redox potential E'0 of -0.258 V and formed mixed disulfides with glutathione and cysteine. MIF-(50-65) but not C57S/C60S-MIF-(50-65) had oxidoreductase activity in vitro. Intriguingly, MIF-(50-65) exhibited MIF-like cellular activities. The peptide but not its variant had glucocorticoid overriding and proliferation-enhancing activity and stimulated ERK1/2 phosphorylation. MIF-(50-65) and its variant bound to the MIF-binding protein JAB1 and enhanced cellular levels of p27Kip1. As the peptide and its variant were endocytosed at similar efficiency, sequence 50-65 appears sufficient for the JAB1-related effects of MIF, whereas other activities require CXXC. Cyclo-57,60-[Asp57,Dap60]MIF-(50-65) activated ERK1/2, indicating that CXXC-dependent disulfide and beta-turn formation is associated with an activity-inducing conformation. We conclude that CXXC and sequence 50-65 are critical for the activities of MIF. MIF-(50-65) is a surprisingly short sequence with MIF-like functions that could be an excellent molecular template for MIF therapeutics.
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Affiliation(s)
- Mai Tuyet Nguyen
- Division of Biochemistry and Molecular Cell Biology, Institute of Biochemistry, University Hospital RWTH Aachen, D-52074 Aachen, Germany
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34
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Dong J, Wan Z, Popov M, Carey PR, Weiss MA. Insulin assembly damps conformational fluctuations: Raman analysis of amide I linewidths in native states and fibrils. J Mol Biol 2003; 330:431-42. [PMID: 12823980 DOI: 10.1016/s0022-2836(03)00536-9] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The crystal structure of insulin has been investigated in a variety of dimeric and hexameric assemblies. Interest in dynamics has been stimulated by conformational variability among crystal forms and evidence suggesting that the functional monomer undergoes a conformational change on receptor binding. Here, we employ Raman spectroscopy and Raman microscopy to investigate well-defined oligomeric species: monomeric and dimeric analogs in solution, native T(6) and R(6) hexamers in solution and corresponding polycrystalline samples. Remarkably, linewidths of Raman bands associated with the polypeptide backbone (amide I) exhibit progressive narrowing with successive self-assembly. Whereas dimerization damps fluctuations at an intermolecular beta-sheet, deconvolution of the amide I band indicates that formation of hexamers stabilizes both helical and non-helical elements. Although the structure of a monomer in solution resembles a crystallographic protomer, its encagement in a native assembly damps main-chain fluctuations. Further narrowing of a beta-sheet-specific amide I band is observed on reorganization of insulin in a cross-beta fibril. Enhanced flexibility of the native insulin monomer is in accord with molecular dynamics simulations. Such conformational fluctuations may initiate formation of an amyloidogenic nucleus and enable induced fit on receptor binding.
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Affiliation(s)
- Jian Dong
- Department of Biochemistry, Case Western Reserve University School of Medicine, 10900 Euclid Avenue SOM-W427, Cleveland, OH 44106-4935, USA
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35
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Guo ZY, Tang YH, Wang S, Feng YM. Contribution of the absolutely conserved B8Gly to the foldability of insulin. Biol Chem 2003; 384:805-9. [PMID: 12817477 DOI: 10.1515/bc.2003.089] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
B8Gly is absolutely conserved in insulin from different species, and in other members of the insulin superfamily the corresponding position is always occupied by a Gly residue. However, the reasons for its conservation are still unclear; probably many factors contribute to this phenomenon. In our previous work, B8Gly was replaced by an Ala residue, which suggested that biological activity is one of the factors contributing to its conservation. In order to identify more factors contributing to this positional conservation, the secretion efficiency, structural stability, disulfide stability, and in vitro refolding of single-chain insulin (PIP) and a mutant with B8Gly replaced by Ala, were investigated. Compared with wild-type PIP, the B8Ala replacement decreased the secretion efficiency, structural stability, disulfide stability, and in vitro refolding efficiency of the PIP sequence. These results suggest that B8Gly is important to the secretion, folding, and stability of the insulin sequence.
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Affiliation(s)
- Zhan-Yun Guo
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, People's Republic of China
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36
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Liu M, Ramos-Castañeda J, Arvan P. Role of the connecting peptide in insulin biosynthesis. J Biol Chem 2003; 278:14798-805. [PMID: 12590147 DOI: 10.1074/jbc.m212070200] [Citation(s) in RCA: 48] [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
In single-chain insulins (SCIs), the C terminus of the insulin B-chain is contiguous with the N terminus of the A-chain, connected by a short bioengineered linker sequence. SCIs have been proposed to offer potential benefit for gene therapy of diabetes (Lee, H. C., Kim, S. J., Kim, K. S., Shin, H. C., and Yoon, J. W. (2000) Nature 408, 483-488) yet relatively little is known about their folding, intracellular transport, or secretion from mammalian cells. Because SCIs can be considered as mutant proinsulin (with selective shortening of the 35-amino acid connecting peptide that normally includes two sets of flanking dibasic residues), they offer insights into understanding the role of the connecting peptide in insulin biosynthesis. Herein we have explored the relationship of the linker sequence to SCI biosynthesis, folding, and intracellular transport in transiently transfected HEK293 or Chinese hamster ovary cells or in stably transfected AtT20 cells. Despite previous reports that direct linkage of B- and A-chains produces a structure isomorphous with authentic two-chain insulin, we find that constructs with short linkers tend to be synthesized at lower levels, with a significant fraction of molecules exhibiting improper disulfide bonding. Nevertheless, disulfide-mispaired isoforms from a number of different SCI constructs are secreted. While this suggests that a novel folded state goes unrecognized by secretory pathway quality control, we find that misfolded SCIs are detected at higher levels in Chinese hamster ovary cells with artificially activated unfolded protein response mediated by inducible overexpression of active ATF-6. Such a maneuver allows analysis of more seriously misfolded mutants with further foreshortening of the linker sequence or loss (by mutation) of the insulin interchain disulfide bonds.
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Affiliation(s)
- Ming Liu
- Diabetes Research and Training Center and the Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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37
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Yan H, Guo ZY, Gong XW, Xi D, Feng YM. A peptide model of insulin folding intermediate with one disulfide. Protein Sci 2003; 12:768-75. [PMID: 12649435 PMCID: PMC2323835 DOI: 10.1110/ps.0237203] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Insulin folds into a unique three-dimensional structure stabilized by three disulfide bonds. Our previous work suggested that during in vitro refolding of a recombinant single-chain insulin (PIP) there exists a critical folding intermediate containing the single disulfide A20-B19. However, the intermediate cannot be trapped during refolding because once this disulfide is formed, the remaining folding process is very quick. To circumvent this difficulty, a model peptide ([A20-B19]PIP) containing the single disulfide A20-B19 was prepared by protein engineering. The model peptide can be secreted from transformed yeast cells, but its secretion yield decreases 2-3 magnitudes compared with that of the wild-type PIP. The physicochemical property analysis suggested that the model peptide adopts a partially folded conformation. In vitro, the fully reduced model peptide can quickly and efficiently form the disulfide A20-B19, which suggested that formation of the disulfide A20-B19 is kinetically preferred. In redox buffer, the model peptide is reduced gradually as the reduction potential is increased, while the disulfides of the wild-type PIP are reduced in a cooperative manner. By analysis of the model peptide, it is possible to deduce the properties of the critical folding intermediate with the single disulfide A20-B19.
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Affiliation(s)
- Han Yan
- Department of Bioengineering, Xi'an Jiaotong University, Xi'an 710049, China
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38
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Hua QX, Nakagawa SH, Wilken J, Ramos RR, Jia W, Bass J, Weiss MA. A divergent INS protein in Caenorhabditis elegans structurally resembles human insulin and activates the human insulin receptor. Genes Dev 2003; 17:826-31. [PMID: 12654724 PMCID: PMC196032 DOI: 10.1101/gad.1058003] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Caenorhabditis elegans contains a family of putative insulin-like genes proposed to regulate dauer arrest and senescence. These sequences often lack characteristic sequence features of human insulin essential for its folding, structure, and function. Here, we describe the structure and receptor-binding properties of INS-6, a single-chain polypeptide expressed in specific neurons. Despite multiple nonconservative changes in sequence, INS-6 recapitulates an insulin-like fold. Although lacking classical receptor-binding determinants, INS-6 binds to and activates the human insulin receptor. Its activity is greater than that of an analogous single-chain human insulin analog.
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Affiliation(s)
- Qing-Xin Hua
- Department of Biochemistry, Case Western Reserve School of Medicine, Cleveland, OH 44106, USA
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39
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Zhang BY, Liu M, Arvan P. Behavior in the eukaryotic secretory pathway of insulin-containing fusion proteins and single-chain insulins bearing various B-chain mutations. J Biol Chem 2003; 278:3687-93. [PMID: 12446709 DOI: 10.1074/jbc.m209474200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the secretory pathway, endoproteolytic cleavage of the insulin precursor protein promotes a change in the biophysical properties of the processed insulin product, and this may be relevant for its intracellular trafficking. We have now studied several independent point mutants contained within the insulin B-chain, S9D, H10D, V12E (called B9D, B10D, and B12E), as well as the double point mutant P28K,K29P (B28K,B29P), that have been reported to inhibit insulin oligomerization. In yeast cells, the unprocessed precursor of each of these mutants is secreted, whereas >90% of the endoproteolytically released single-chain insulin moiety is retained intracellularly; a large portion of the B9D, B10D, and B12E single-chain insulins exhibit abnormally slow mobility upon nonreducing SDS-PAGE, despite normal mobility upon reducing SDS-PAGE. Although no free thiols can be detected, each of these mutants exhibits increased disulfide accessibility to dithiothreitol. After dithiothreitol treatment, a portion of the molecules can reoxidize to a form more compact than the original single-chain insulin mutants formed in vivo (indicating initial disulfide mispairing). Disulfide mispairing of a fraction of B9D, B10D, and B12E mutants also occurs in the context of single-chain insulin and even in authentic proinsulin expressed within the secretory pathway of mammalian cells. We conclude that analyses of the intracellular trafficking of certain oligomerization-defective insulin mutants is complicated by the formation of disulfide isomers in the secretory pathway.
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Affiliation(s)
- Bao-yan Zhang
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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40
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Zhang BY, Chang A, Kjeldsen TB, Arvan P. Intracellular retention of newly synthesized insulin in yeast is caused by endoproteolytic processing in the Golgi complex. J Cell Biol 2001; 153:1187-98. [PMID: 11402063 PMCID: PMC2192022 DOI: 10.1083/jcb.153.6.1187] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
An insulin-containing fusion protein (ICFP, encoding the yeast prepro-alpha factor leader peptide fused via a lysine-arginine cleavage site to a single chain insulin) has been expressed in Saccharomyces cerevisiae where it is inefficiently secreted. Single gene disruptions have been identified that cause enhanced immunoreactive insulin secretion (eis). Five out of six eis mutants prove to be vacuolar protein sorting (vps)8, vps35, vps13, vps4, and vps36, which affect Golgi<-->endosome trafficking. Indeed, in wild-type yeast insulin is ultimately delivered to the vacuole, whereas vps mutants secrete primarily unprocessed ICFP. Disruption of KEX2, which blocks intracellular processing to insulin, quantitatively reroutes ICFP to the cell surface, whereas loss of the Vps10p sorting receptor is without effect. Secretion of unprocessed ICFP is not based on a dominant secretion signal in the alpha-leader peptide. Although insulin sorting mediated by Kex2p is saturable, Kex2p functions not as a sorting receptor but as a protease: replacement of Kex2p by truncated secretory Kex2p (which travels from Golgi to cell surface) still causes endoproteolytic processing and intracellular insulin retention. Endoproteolysis promotes a change in insulin's biophysical properties. B5His residues normally participate in multimeric insulin packing; a point mutation at this position permits ICFP processing but causes the majority of processed insulin to be secreted. The data argue that multimeric assembly consequent to endoproteolytic maturation regulates insulin sorting in the secretory pathway.
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Affiliation(s)
- Bao-yan Zhang
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York 10461
| | - Amy Chang
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York 10461
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York 10461
| | | | - Peter Arvan
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York 10461
- Division of Endocrinology, Albert Einstein College of Medicine, Bronx, New York 10461
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41
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Kleemann R, Rorsman H, Rosengren E, Mischke R, Mai NT, Bernhagen J. Dissection of the enzymatic and immunologic functions of macrophage migration inhibitory factor. Full immunologic activity of N-terminally truncated mutants. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:7183-93. [PMID: 11106430 DOI: 10.1046/j.1432-1327.2000.01823.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Macrophage migration inhibitory factor (MIF) is a cytokine with broad regulatory functions in innate immunity. MIF belongs to the few cytokines displaying catalytic activities, i.e. MIF has a Pro2-dependent tautomerase and a Cys-Ala-Leu-Cys (CALC) cysteine-based thiol-protein oxidoreductase activity. Previous studies have addressed the roles of the catalytic site residues and the C-terminus. The two activities have not been directly compared. Here we report on the N-terminal mutational analysis and minimization of MIF and on a dissection of the two catalytic activities by comparing mutants P2AMIF, Delta4MIF, Delta5MIF, Delta6MIF, Delta7MIF, Delta8MIF, and Delta10MIF with the cysteine mutants of MIF. As N-terminal deletion was predicted to interfere with protein structure due to disruption of the central beta sheet, it was surprising that deletion of up to six N-terminal residues resulted in normally expressed proteins with wild-type conformation. Strikingly, such mutants exhibited full MIF-specific immunologic activity. While mutation of Pro2 eliminated tautomerase activity, the CALC cysteine residues had no influence on this activity. However, mutant C81SMIF, which otherwise has full biologic activity, only had 32% tautomerase activity. Deletion of four N-terminal residues did not interfere with insulin reduction by MIF. By contrast, reduction of 2-hydroxyethyldisulfide (HED) was markedly affected by N-terminal manipulation, with P2AMIF and Delta2MIF exhibiting 40% activity, and Delta4MIF completely failing to reduce HED. This study constitutes the first comparison of the two catalytic activities of MIF and should assist in understanding the molecular links between the catalytic and immunologic activities of this cytokine and in providing guidelines for N-terminal protein minimization.
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Affiliation(s)
- R Kleemann
- Laboratory of Biochemistry, Institute for Interfacial Engineering, University of Stuttgart, Germany
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42
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Laajoki LG, Francis GL, Wallace JC, Carver JA, Keniry MA. Solution structure and backbone dynamics of long-[Arg(3)]insulin-like growth factor-I. J Biol Chem 2000; 275:10009-15. [PMID: 10744677 DOI: 10.1074/jbc.275.14.10009] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Long-[Arg(3)]insulin-like growth factor-I (IGF-I) is a potent analog of insulin-like growth factor-I that has been modified by a Glu(3) --> Arg mutation and a 13-amino acid extension appended to the N terminus. We have determined the solution structure of (15)N-labeled Long-[Arg(3)]-IGF-I using high resolution NMR and restrained molecular dynamics techniques to a precision of 0.82 +/- 0.28 A root mean square deviation for the backbone heavy atoms in the three alpha-helices and 3.5 +/- 0.9 A root mean square deviation for all backbone heavy atoms excluding the 8 N-terminal residues and the 8 C-terminal eight residues. Overall, the structure of the IGF-I domain is consistent with earlier studies of IGF-I with some minor changes remote from the N terminus. The major variations in the structure, compared with IGF-I, occur at the N terminus with a substantial reorientation of the N-terminal three residues of the IGF-I domain. These results are interpreted in terms of the lower binding affinity for insulin-like growth factor-binding proteins. The backbone dynamics of Long-[Arg(3)]IGF-I were investigated using (15)N nuclear spin relaxation and the heteronuclear nuclear Overhauser enhancement (NOE). There is a considerable degree of flexibility in Long-[Arg(3)]IGF-I, even in the alpha-helices, as indicated by an average ((1)H)(15)N NOE of 0.55 for the regions. The largest heteronuclear NOEs are observed in the helical regions, lower heteronuclear NOEs are observed in the C-domain loop separating helix 1 from helix 2, and negative heteronuclear NOEs are observed in the N-terminal extension and at the C terminus. Despite these data indicating conformational flexibility for the N-terminal extension, slow amide proton exchange was observed for some residues in this region, suggesting some transitory structure does exist, possibly a molten helix. A certain degree of flexibility may be necessary in all insulin-like growth factors to enable association with various receptors and binding proteins.
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Affiliation(s)
- L G Laajoki
- Research School of Chemistry, The Australian National University, Canberra, Australian Capital Territory 2601, South Australia 5000
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43
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Hober S, Lundström Ljung J, Uhlén M, Nilsson B. Insulin-like growth factors I and II are unable to form and maintain their native disulfides under in vivo redox conditions. FEBS Lett 1999; 443:271-6. [PMID: 10025946 DOI: 10.1016/s0014-5793(98)01737-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Insulin-like growth factor (IGF) I does not quantitatively form its three native disulfide bonds in the presence of 10 mM reduced and 1 mM oxidized glutathione in vitro [Hober, S. et al. (1992) Biochemistry 31, 1749-1756]. In this paper, we show (i) that both IGF-I and IGF-II are unable to form and maintain their native disulfide bonds at redox conditions that are similar to the situation in the secretory vesicles in vivo and (ii) that the presence of protein disulfide isomerase does not overcome this problem. The results indicate that the previously described thermodynamic disulfide exchange folding problem of IGF-I in vitro is also present in vivo. Speculatively, we suggest that the thermodynamic disulfide exchange properties of IGF-I and II are biologically significant for inactivation of the unbound growth factors by disulfide exchange reactions to generate variants destined for rapid clearance.
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Affiliation(s)
- S Hober
- Department of Biotechnology, Royal Institute of Technology, Stockholm, Sweden.
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