1
|
Pujahari SR, Purusottam RN, Mali PS, Sarkar S, Khaneja N, Vajpai N, Kumar A. Exploring the Higher Order Structure and Conformational Transitions in Insulin Microcrystalline Biopharmaceuticals by Proton-Detected Solid-State Nuclear Magnetic Resonance at Natural Abundance. Anal Chem 2024; 96:4756-4763. [PMID: 38326990 DOI: 10.1021/acs.analchem.3c04040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2024]
Abstract
The integrity of a higher order structure (HOS) is an essential requirement to ensure the efficacy, stability, and safety of protein therapeutics. Solution-state nuclear magnetic resonance (NMR) occupies a unique niche as one of the most promising methods to access atomic-level structural information on soluble biopharmaceutical formulations. Another major class of drugs is poorly soluble, such as microcrystalline suspensions, which poses significant challenges for the characterization of the active ingredient in its native state. Here, we have demonstrated a solid-state NMR method for HOS characterization of biopharmaceutical suspensions employing a selective excitation scheme under fast magic angle spinning (MAS). The applicability of the method is shown on commercial insulin suspensions at natural isotopic abundance. Selective excitation aided with proton detection and non-uniform sampling (NUS) provides improved sensitivity and resolution. The enhanced resolution enabled us to demonstrate the first experimental evidence of a phenol-escaping pathway in insulin, leading to conformational transitions to different hexameric states. This approach has the potential to serve as a valuable means for meticulously examining microcrystalline biopharmaceutical suspensions, which was previously not attainable in their native formulation states and can be seamlessly extended to other classes of biopharmaceuticals such as mAbs and other microcrystalline proteins.
Collapse
Affiliation(s)
- Soumya Ranjan Pujahari
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai Mumbai 400076, India
| | - Rudra N Purusottam
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai Mumbai 400076, India
| | - Pramod S Mali
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai Mumbai 400076, India
| | - Sambeda Sarkar
- System and Control Engineering, Indian Institute of Technology, Bombay, Powai Mumbai 400076, India
| | - Navin Khaneja
- System and Control Engineering, Indian Institute of Technology, Bombay, Powai Mumbai 400076, India
| | - Navratna Vajpai
- Biocon Biologics Limited, Biocon SEZ, Plot No. 2 & 3, Phase IV-B.I.A, Bommasandra-Jigani Link Road, Bangalore 560099, India
| | - Ashutosh Kumar
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai Mumbai 400076, India
| |
Collapse
|
2
|
Karavassili F, Valmas A, Fili S, Georgiou CD, Margiolaki I. In Quest for Improved Drugs against Diabetes: The Added Value of X-ray Powder Diffraction Methods. Biomolecules 2017; 7:E63. [PMID: 28829407 PMCID: PMC5618244 DOI: 10.3390/biom7030063] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Revised: 08/14/2017] [Accepted: 08/16/2017] [Indexed: 01/04/2023] Open
Abstract
Human insulin (HI) is a well-characterized natural hormone which regulates glycose levels into the blood-stream and is widely used for diabetes treatment. Numerous studies have manifested that despite significant efforts devoted to structural characterization of this molecule and its complexes with organic compounds (ligands), there is still a rich diagram of phase transitions and novel crystalline forms to be discovered. Towards the improvement of drug delivery, identification of new insulin polymorphs from polycrystalline samples, simulating the commercially available drugs, is feasible today via macromolecular X-ray powder diffraction (XRPD). This approach has been developed, and is considered as a respectable method, which can be employed in biosciences for various purposes, such as observing phase transitions and characterizing bulk pharmaceuticals. An overview of the structural studies on human insulin complexes performed over the past decade employing both synchrotron and laboratory sources for XRPD measurements, is reported herein. This review aims to assemble all of the recent advances in the diabetes treatment field in terms of drug formulation, verifying in parallel the efficiency and applicability of protein XRPD for quick and accurate preliminary structural characterization in the large scale.
Collapse
Affiliation(s)
- Fotini Karavassili
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece.
| | - Alexandros Valmas
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece.
| | - Stavroula Fili
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece.
| | - Christos D Georgiou
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece.
| | - Irene Margiolaki
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece.
| |
Collapse
|
3
|
Koch H, Noack K, Will S. Raman excess spectroscopy vs. principal component analysis: probing the intermolecular interactions between chiral molecules and imidazolium-based ionic liquids. Phys Chem Chem Phys 2016; 18:28370-28375. [DOI: 10.1039/c6cp04372k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
PCA: Optical separation of glucose enantiomers based on enantioselective interactions.
Collapse
Affiliation(s)
- H. Koch
- Lehrstuhl für Technische Thermodynamik (LTT) and Erlangen Graduate School in Advanced Optical Technologies (SAOT)
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - K. Noack
- Lehrstuhl für Technische Thermodynamik (LTT) and Erlangen Graduate School in Advanced Optical Technologies (SAOT)
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - S. Will
- Lehrstuhl für Technische Thermodynamik (LTT) and Erlangen Graduate School in Advanced Optical Technologies (SAOT)
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| |
Collapse
|
4
|
Fili S, Valmas A, Norrman M, Schluckebier G, Beckers D, Degen T, Wright J, Fitch A, Gozzo F, Giannopoulou AE, Karavassili F, Margiolaki I. Human insulin polymorphism upon ligand binding and pH variation: the case of 4-ethylresorcinol. IUCRJ 2015; 2:534-44. [PMID: 26306195 PMCID: PMC4547821 DOI: 10.1107/s2052252515013159] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 07/08/2015] [Indexed: 06/04/2023]
Abstract
This study focuses on the effects of the organic ligand 4-ethylresorcinol on the crystal structure of human insulin using powder X-ray crystallography. For this purpose, systematic crystallization experiments have been conducted in the presence of the organic ligand and zinc ions within the pH range 4.50-8.20, while observing crystallization behaviour around the isoelectric point of insulin. High-throughput crystal screening was performed using a laboratory X-ray diffraction system. The most representative samples were selected for synchrotron X-ray diffraction measurements, which took place at the European Synchrotron Radiation Facility (ESRF) and the Swiss Light Source (SLS). Four different crystalline polymorphs have been identified. Among these, two new phases with monoclinic symmetry have been found, which are targets for the future development of microcrystalline insulin drugs.
Collapse
Affiliation(s)
- S. Fili
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece
| | - A. Valmas
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece
| | - M. Norrman
- Diabetes Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Malov, Denmark
| | - G. Schluckebier
- Diabetes Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Malov, Denmark
| | - D. Beckers
- PANalytical B.V., Lelyweg 1, 7602 EA Almelo, The Netherlands
| | - T. Degen
- PANalytical B.V., Lelyweg 1, 7602 EA Almelo, The Netherlands
| | - J. Wright
- European Synchrotron Radiation Facility, CS40220, F-38043 Grenoble CEDEX 9, France
| | - A. Fitch
- European Synchrotron Radiation Facility, CS40220, F-38043 Grenoble CEDEX 9, France
| | - F. Gozzo
- Excelsus Structural Solutions, Belgium
| | - A. E. Giannopoulou
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece
| | - F. Karavassili
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece
| | - I. Margiolaki
- Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, GR-26500 Patras, Greece
| |
Collapse
|
5
|
Kundu PP, Bhowmick T, Swapna G, Pavan Kumar GV, Nagaraja V, Narayana C. Allosteric transition induced by Mg²⁺ ion in a transactivator monitored by SERS. J Phys Chem B 2014; 118:5322-30. [PMID: 24783979 DOI: 10.1021/jp5000733] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We demonstrate the utility of the surface-enhanced Raman spectroscopy (SERS) to monitor conformational transitions in protein upon ligand binding. The changes in protein's secondary and tertiary structures were monitored using amide and aliphatic/aromatic side chain vibrations. Changes in these bands are suggestive of the stabilization of the secondary and tertiary structure of transcription activator protein C in the presence of Mg(2+) ion, whereas the spectral fingerprint remained unaltered in the case of a mutant protein, defective in Mg(2+) binding. The importance of the acidic residues in Mg(2+) binding, which triggers an overall allosteric transition in the protein, is visualized in the molecular model. The present study thus opens up avenues toward the application of SERS as a potential tool for gaining structural insights into the changes occurring during conformational transitions in proteins.
Collapse
Affiliation(s)
- Partha P Kundu
- Light Scattering Laboratory, Chemistry and Physics of Material Unit, Jawaharlal Nehru Center for Advanced Scientific Research , Jakkur, Bangalore 560064, India
| | | | | | | | | | | |
Collapse
|
6
|
Zeng G, Shou JJ, Li KK, Zhang YH. In-situ confocal Raman observation of structural changes of insulin crystals in sequential dehydration process. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1631-40. [DOI: 10.1016/j.bbapap.2011.09.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2011] [Revised: 09/01/2011] [Accepted: 09/02/2011] [Indexed: 11/25/2022]
|
7
|
Muzaffar M, Ahmad A. The mechanism of enhanced insulin amyloid fibril formation by NaCl is better explained by a conformational change model. PLoS One 2011; 6:e27906. [PMID: 22132167 PMCID: PMC3221682 DOI: 10.1371/journal.pone.0027906] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2011] [Accepted: 10/27/2011] [Indexed: 01/05/2023] Open
Abstract
The high propensity of insulin to fibrillate causes severe biomedical and biotechnological complications. Insulin fibrillation studies attain significant importance considering the prevalence of diabetes and the requirement of functional insulin in each dose. Although studied since the early years of the 20(th) century, elucidation of the mechanism of insulin fibrillation has not been understood completely. We have previously, through several studies, shown that insulin hexamer dissociates into monomer that undergoes partial unfolding before converting into mature fibrils. In this study we have established that NaCl enhances insulin fibrillation mainly due to subtle structural changes and is not a mere salt effect. We have carried out studies both in the presence and absence of urea and Gdn.HCl and compared the relationship between conformation of insulin induced by urea and Gdn.HCl with respect to NaCl at both pH 7.4 (hexamer) and pH 2 (monomer). Fibril formation was followed with a Thioflavin T assay and structural changes were monitored by circular dichroism and size-exclusion chromatography. The results show salt-insulin interactions are difficult to classify as commonly accepted Debye-Hückel or Hofmeister series interactions but instead a strong correlation between the association states and conformational states of insulin and their propensity to fibrillate is evident.
Collapse
Affiliation(s)
- Mahvish Muzaffar
- Department of Biological Chemistry and Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
| | | |
Collapse
|
8
|
Maltesen; MJ, Bjerregaard S, Hovgaard L, Havelund S, Van De Weert M. Analysis of Insulin Allostery in Solution and Solid State With FTIR. J Pharm Sci 2009; 98:3265-77. [DOI: 10.1002/jps.21736] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
9
|
Keidel D, Bonaccio M, Ghaderi N, Niks D, Borchardt D, Dunn MF. 1H{19F} NOE NMR Structural Signatures of the Insulin R6Hexamer: Evidence of a Capped HisB10 Site in Aryl- and Arylacryloyl-carboxylate Complexes. Chembiochem 2009; 10:450-3. [DOI: 10.1002/cbic.200800746] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
10
|
Ligand escape pathways and (un)binding free energy calculations for the hexameric insulin-phenol complex. Biophys J 2008; 95:4193-204. [PMID: 18676643 DOI: 10.1529/biophysj.108.139675] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cooperative binding of phenolic species to insulin hexamers is known to stabilize pharmaceutical preparations of the hormone. Phenol dissociation is rapid on hexamer dissolution timescales, and phenol unbinding upon dilution is likely the first step in the conversion of (pharmaceutical) hexameric insulin to the active monomeric form upon injection. However, a clear understanding of the determinants of the rates of phenol unbinding remains obscure, chiefly because residues implicated in phenol exchange as determined by NMR are not all associated with likely unbinding routes suggested by the best-resolved hexamer structures. We apply random acceleration molecular dynamics simulation to identify potential escape routes of phenol from hydrophobic cavities in the hexameric insulin-phenol complex. We find three major pathways, which provide new insights into (un)binding mechanisms for phenol. We identify several residues directly participating in escape events that serve to resolve ambiguities from recent NMR experiments. Reaction coordinates for dissociation of phenol are developed based on these exit pathways. Potentials of mean force along the reaction coordinate for each pathway are resolved using multiple independent steered molecular dynamics simulations with second-order cumulant expansion of Jarzynski's equality. Our results for DeltaF agree reasonably well within the range of known experimental and previous simulation magnitudes of this quantity. Based on structural analysis and energetic barriers for each pathway, we suggest a plausible preferred mechanism of phenolic exchange that differs from previous mechanisms. Several weakly-bound metastable states are also observed for the first time in the phenol dissociation reaction.
Collapse
|
11
|
Huus K, Havelund S, Olsen HB, van de Weert M, Frokjaer S. Chemical and Thermal Stability of Insulin: Effects of Zinc and Ligand Binding to the Insulin Zinc-Hexamer. Pharm Res 2006; 23:2611-20. [PMID: 16969698 DOI: 10.1007/s11095-006-9098-y] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2006] [Accepted: 06/23/2006] [Indexed: 11/26/2022]
Abstract
PURPOSE To study the correlation between the thermal and chemical stability of insulin formulations with various insulin hexamer ligands. MATERIALS AND METHODS The thermal stability was investigated using differential scanning calorimetry (DSC) and near-UV circular dichroism (NUV-CD). The formation of chemical degradation products was studied with reversed-phase and size-exclusion chromatography and mass spectrometry. RESULTS An excellent correlation between the thermal stabilization by ligand binding and the deamidation of Asn(B3) was observed. The correlation between thermal stability and the formation of covalent dimer and other insulin related products was less clear. Zinc was found to specifically increase the deamidation and covalent dimer formation rate when the insulin hexamer was not further stabilized by phenolic ligand. Thiocyanate alone had no effect on the thermal stability of the insulin zinc-hexamer but significantly improved the chemical stability at 37 degrees C. At low temperatures thiocyanate induced a conformational change in the insulin hexamer. NUV-CD thermal scans revealed that this effect decreased with temperature; when the thermal denaturation temperature was reached, the effect was eliminated. CONCLUSIONS Thermal stability can be used to predict the rate of Asn(B3) deamidation in human insulin. Chemical degradation processes that do not rely on the structural stability of the protein do not necessarily correlate to the thermal stability.
Collapse
Affiliation(s)
- Kasper Huus
- Department of Pharmaceutics and Analytical Chemistry, The Danish University of Pharmaceutical Sciences, 2100 Copenhagen, Denmark.
| | | | | | | | | |
Collapse
|
12
|
Drachev VP, Thoreson MD, Khaliullin EN, Davisson VJ, Shalaev VM. Surface-Enhanced Raman Difference between Human Insulin and Insulin Lispro Detected with Adaptive Nanostructures. J Phys Chem B 2004. [DOI: 10.1021/jp047254h] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Vladimir P. Drachev
- School of Electrical and Computer Engineering and School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Mark D. Thoreson
- School of Electrical and Computer Engineering and School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Eldar N. Khaliullin
- School of Electrical and Computer Engineering and School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907
| | - V. Jo Davisson
- School of Electrical and Computer Engineering and School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Vladimir M. Shalaev
- School of Electrical and Computer Engineering and School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907
| |
Collapse
|
13
|
Zhang D, Mrozek MF, Xie Y, Ben-Amotz D. Chemical segregation and reduction of Raman background interference using drop coating deposition. APPLIED SPECTROSCOPY 2004; 58:929-933. [PMID: 15324499 DOI: 10.1366/0003702041655430] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A new application of the recently described drop coating deposition Raman (DCDR) method facilitates the segregation and independent spectral characterization of mixture components. The quality of the normal (un-enhanced) Raman spectra are significantly improved as a result of reduced spectral interference from fluorescent impurities and buffer compounds. Fluorescence of commercial amino acid (O-phospho-L-serine) and protein (myoglobin) samples is reduced by over an order of magnitude using DCDR, more effectively than prolonged photo-bleaching. Furthermore, DCDR is used to obtain high-quality Raman spectra of proteins, lysozyme, and insulin, derived from solutions with up to 1000-fold excess buffer concentration. Possible thermodynamic and kinetic contributions to the observed segregation phenomena are discussed.
Collapse
Affiliation(s)
- Dongmao Zhang
- Purdue University, Department of Chemistry, West Lafayette, Indiana 47907, USA
| | | | | | | |
Collapse
|
14
|
Zhang D, Xie Y, Mrozek MF, Ortiz C, Davisson VJ, Ben-Amotz D. Raman detection of proteomic analytes. Anal Chem 2004; 75:5703-9. [PMID: 14588009 DOI: 10.1021/ac0345087] [Citation(s) in RCA: 152] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The compatibility of nonenhanced Raman spectroscopy with chromatographic and mass spectroscopic proteomic sensing is demonstrated for the first time. High-quality normal Raman spectra are derived from protein solutions with concentrations down to 1 microM and 1 fmol of protein nondestructively probed within the excitation laser beam. These results are obtained using a drop coating deposition Raman (DCDR) method in which the solution of interest is microdeposited (or microprinted) on a compatible substrate, followed by solvent evaporation and backscattering detection. Representative applications include the DCDR detection of insulin derived from an HPLC fraction, nondestructive DCDR followed by MALDI-TOF of lysozyme, the DCDR detection of protein spots deposited using an ink-jet microprinter, and the identification of spectral differences between glycan isomers of equal mass (such as those derived from posttranslationally modified proteins).
Collapse
Affiliation(s)
- Dongmao Zhang
- Department of Chemistry and Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indianapolis, Indiana 47907, USA
| | | | | | | | | | | |
Collapse
|
15
|
Olsen HB, Leuenberger-Fisher MR, Kadima W, Borchardt D, Kaarsholm NC, Dunn MF. Structural signatures of the complex formed between 3-nitro-4-hydroxybenzoate and the Zn(II)-substituted R(6) insulin hexamer. Protein Sci 2003; 12:1902-13. [PMID: 12930990 PMCID: PMC2323988 DOI: 10.1110/ps.03116403] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
3-Nitro-4-hydroxybenzoate (3N4H) is a probe of the structure and dynamics of the metal-centered His B10 assembly sites of the insulin hexamer. Each His B10 site consists of a approximately 12 A-long cavity situated on the threefold symmetry axis. These sites play an important role in the storage and release of insulin in vivo. The allosteric behavior of the insulin hexamer is modulated by ligand binding to the His B10 zinc sites and to the phenolic pockets. Binding to these sites drives transitions among three allosteric states, designated T(6), T(3)R(3), and R(6). Although a wide variety of mono anions bind to the His B10 zinc sites of R(3), X-ray structures of ligands complexed to this site exist only for H(2)O, Cl(-), and SCN(-). This work combines one- and two-dimensional (1)H NMR and UV-Vis absorbance studies of the structure and dynamics of the 3N4H complex, which establish the following: (1). relative to the NMR time scale, 3N4H exchange between free and bound states is slow, while flipping among three equivalent orientations about the site threefold axis is fast; (2). binding of 3N4H perturbs resonances within the His B10 zinc site and generates NOEs between ligand resonances and the insulin C-alpha and side chain resonances of ValB2, AsnB3, LeuB6, and CysB7; and (3).3N4H exchange for other ligands is limited by a protein conformational transition. These results are consistent with coordination of the 3N4H carboxylate to the His B10 zinc ion and van der Waals interactions with Val B2, Asn B3, Leu B6, and Cys A7.
Collapse
|
16
|
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.
Collapse
Affiliation(s)
- Jian Dong
- Department of Biochemistry, Case Western Reserve University School of Medicine, 10900 Euclid Avenue SOM-W427, Cleveland, OH 44106-4935, USA
| | | | | | | | | |
Collapse
|