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Abstract
Glycans, carbohydrate molecules in the realm of biology, are present as biomedically important glycoconjugates and a characteristic aspect is that their structures in many instances are branched. In determining the primary structure of a glycan, the sugar components including the absolute configuration and ring form, anomeric configuration, linkage(s), sequence, and substituents should be elucidated. Solution state NMR spectroscopy offers a unique opportunity to resolve all these aspects at atomic resolution. During the last two decades, advancement of both NMR experiments and spectrometer hardware have made it possible to unravel carbohydrate structure more efficiently. These developments applicable to glycans include, inter alia, NMR experiments that reduce spectral overlap, use selective excitations, record tilted projections of multidimensional spectra, acquire spectra by multiple receivers, utilize polarization by fast-pulsing techniques, concatenate pulse-sequence modules to acquire several spectra in a single measurement, acquire pure shift correlated spectra devoid of scalar couplings, employ stable isotope labeling to efficiently obtain homo- and/or heteronuclear correlations, as well as those that rely on dipolar cross-correlated interactions for sequential information. Refined computer programs for NMR spin simulation and chemical shift prediction aid the structural elucidation of glycans, which are notorious for their limited spectral dispersion. Hardware developments include cryogenically cold probes and dynamic nuclear polarization techniques, both resulting in enhanced sensitivity as well as ultrahigh field NMR spectrometers with a 1H NMR resonance frequency higher than 1 GHz, thus improving resolution of resonances. Taken together, the developments have made and will in the future make it possible to elucidate carbohydrate structure in great detail, thereby forming the basis for understanding of how glycans interact with other molecules.
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Affiliation(s)
- Carolina Fontana
- Departamento
de Química del Litoral, CENUR Litoral Norte, Universidad de la República, Paysandú 60000, Uruguay
| | - Göran Widmalm
- Department
of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden,
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2
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Novakovic M, Battistel MD, Azurmendi HF, Concilio MG, Freedberg DI, Frydman L. The Incorporation of Labile Protons into Multidimensional NMR Analyses: Glycan Structures Revisited. J Am Chem Soc 2021; 143:8935-8948. [PMID: 34085814 PMCID: PMC8297728 DOI: 10.1021/jacs.1c04512] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Glycan structures
are often stabilized by a repertoire of hydrogen-bonded
donor/acceptor groups, revealing longer-lived structures that could
represent biologically relevant conformations. NMR provides unique
data on these hydrogen-bonded networks from multidimensional experiments
detecting cross-peaks resulting from through-bond (TOCSY) or through-space
(NOESY) interactions. However, fast OH/H2O exchange, and
the spectral proximity among these NMR resonances, hamper the use
of glycans’ labile protons in such analyses; consequently,
studies are often restricted to aprotic solvents or supercooled aqueous
solutions. These nonphysiological conditions may lead to unrepresentative
structures or to probing a small subset of accessible conformations
that may miss “active” glycan conformations. Looped,
projected spectroscopy (L-PROSY) has been recently shown to substantially
enhance protein NOESY and TOCSY cross-peaks, for 1Hs that
undergo fast exchange with water. This study shows that even larger
enhancements can be obtained for rapidly exchanging OHs in saccharides,
leading to the retrieval of previously undetectable 2D TOCSY/NOESY
cross-peaks with nonlabile protons. After demonstrating ≥300%
signal enhancements on model monosaccharides, these experiments were
applied at 1 GHz to elucidate the structural network adopted by a
sialic acid homotetramer, used as a model for α,2–8 linked
polysaccharides. High-field L-PROSY NMR enabled these studies at higher
temperatures and provided insight previously unavailable from lower-field
NMR investigations on supercooled samples, involving mostly nonlabile
nuclei. Using L-PROSY’s NOEs and other restraints, a revised
structural model for the homotetramer was obtained combining rigid
motifs and flexible segments, that is well represented by conformations
derived from 40 μs molecular dynamics simulations.
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Affiliation(s)
- Mihajlo Novakovic
- Department of Chemical and Biological Physics, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Marcos D Battistel
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, Maryland 20993, United States
| | - Hugo F Azurmendi
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, Maryland 20993, United States
| | - Maria-Grazia Concilio
- Department of Chemical and Biological Physics, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Darón I Freedberg
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, Maryland 20993, United States
| | - Lucio Frydman
- Department of Chemical and Biological Physics, Weizmann Institute of Science, 76100 Rehovot, Israel
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3
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Hamagami H, Yamaguchi Y, Tanaka H. Chemical Synthesis of Residue-Selectively 13C and 2H Double-Isotope-Labeled Oligosaccharides as Chemical Probes for the NMR-Based Conformational Analysis of Oligosaccharides. J Org Chem 2020; 85:16115-16127. [PMID: 33107296 DOI: 10.1021/acs.joc.0c01939] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The conformational analysis of oligosaccharide is a fundamental issue in glycobiology. NMR measurements of atom-selectively 13C-labeled oligosaccharides have provided valuable information concerning their conformation, which would not be possible using nonlabeled oligosaccharides. The amount of accessible information from an atom-selectively labeled molecule, however, is limited. In this work, we report on the chemical synthesis of residue-selectively 13C- and 2H-labeled oligosaccharides and their use in conformational analysis. 1H NMR measurements of such double isotope-labeled compounds can provide a great deal of information on the dihedral angles across glycosidic linkages. We demonstrated this method in the conformational analyses of some linear and branched β(1,3)-glucan oligosaccharides.
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Affiliation(s)
- Hiroki Hamagami
- Department of Chemical Science and Engineering, Tokyo Institute of Technology, 2-12-1-H101 Ookayama, Meguro, Tokyo 152-8552, Japan
| | - Yoshiki Yamaguchi
- RIKEN-Max-Planck Joint Research Center for Systems Chemical Biology RIKEN Global Research Cluster, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Hiroshi Tanaka
- Department of Chemical Science and Engineering, Tokyo Institute of Technology, 2-12-1-H101 Ookayama, Meguro, Tokyo 152-8552, Japan
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4
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Rönnols J, Engström O, Schnupf U, Säwén E, Brady JW, Widmalm G. Inter-residual Hydrogen Bonding in Carbohydrates Unraveled by NMR Spectroscopy and Molecular Dynamics Simulations. Chembiochem 2019; 20:2519-2528. [PMID: 31066963 DOI: 10.1002/cbic.201900301] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Indexed: 12/15/2022]
Abstract
Carbohydrates, also known as glycans in biological systems, are omnipresent in nature where they as glycoconjugates occur as oligo- and polysaccharides linked to lipids and proteins. Their three-dimensional structure is defined by two or three torsion angles at each glycosidic linkage. In addition, transglycosidic hydrogen bonding between sugar residues may be important. Herein we investigate the presence of these inter-residue interactions by NMR spectroscopy in D2 O/[D6 ]DMSO (70:30) or D2 O and by molecular dynamics (MD) simulations with explicit water as solvent for disaccharides with structural elements α-d-Manp-(1→2)-d-Manp, β-d-GlcpNAc-(1→2)-d-Manp, and α-d-Glcp-(1→4)-β-d-Glcp, all of which have been suggested to exhibit inter-residue hydrogen bonding. For the disaccharide β-d-GlcpNAc-(1→2)-β-d-Manp-OMe, the large extent of O5'⋅⋅⋅HO3 hydrogen bonding as seen from the MD simulation is implicitly supported by the 1 H NMR chemical shift and 3 JHO3,H3 value of the hydroxy proton. In the case of α-d-Glcp-(1→4)-β-d-Glcp-OMe, the existence of a transglycosidic hydrogen bond O2'⋅⋅⋅HO3 was proven by the presence of a cross-peak in 1 H,13 C HSQC-TOCSY experiments as a result of direct TOCSY transfer between HO3 of the reducing end residue and H2' (detected at C2') of the terminal residue. The occurrence of inter-residue hydrogen bonding, albeit transient, is judged important for the stabilization of three-dimensional structures, which may be essential in maintaining a conformational state for carbohydrate-protein interactions of glycans to take place in biologically important environments.
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Affiliation(s)
- Jerk Rönnols
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
| | - Olof Engström
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
| | - Udo Schnupf
- Department of Chemistry and Biochemistry, Bradley University, Peoria, IL, 61625, USA
| | - Elin Säwén
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
| | - John W Brady
- Department of Food Science, Cornell University, Ithaca, NY, 14853, USA
| | - Göran Widmalm
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
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5
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Green AR, Li K, Lockard B, Young RP, Mueller LJ, Larive CK. Investigation of the Amide Proton Solvent Exchange Properties of Glycosaminoglycan Oligosaccharides. J Phys Chem B 2019; 123:4653-4662. [PMID: 31067054 DOI: 10.1021/acs.jpcb.9b01794] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
One-dimensional 1H NMR experiments were conducted for aqueous solutions of glycosaminoglycan oligosaccharides to measure the amide proton temperature coefficients and activation energy barriers for solvent exchange and evaluate the effect of pH on the solvent exchange properties. A library of mono- and oligosaccharides was prepared by enzymatic depolymerization of amide-containing polysaccharides and by chemical modification of heparin and heparan sulfate saccharides including members that contain a 3- O-sulfated glucosamine residue. The systematic evaluation of this saccharide library facilitated assessment of the effects of structural characteristics, such as size, sulfation number and site, and glycosidic linkage, on amide proton solvent exchange rates. Charge repulsion by neighboring negatively charged sulfate and carboxylate groups was found to have a significant impact on the catalysis of amide proton solvent exchange by hydroxide. This observation leads to the conclusion that solvent exchange rates must be interpreted within the context of a given chemical environment. On their own, slow exchange rates do not conclusively establish the involvement of a labile proton in a hydrogen bond, and additional supporting experimental evidence such as reduced temperature coefficients is required.
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Affiliation(s)
- Andrew R Green
- Department of Chemistry , University of California-Riverside , Riverside , California 92501 , United States
| | - Kecheng Li
- Department of Chemistry , University of California-Riverside , Riverside , California 92501 , United States.,Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology , Chinese Academy of Sciences , Qingdao 266071 , China.,Laboratory for Marine Drugs and Bioproducts of Qingdao National Laboratory for Marine Science and Technology , Qingdao 266237 , China
| | - Blake Lockard
- Department of Chemistry , University of California-Riverside , Riverside , California 92501 , United States
| | - Robert P Young
- Department of Chemistry , University of California-Riverside , Riverside , California 92501 , United States.,Environmental Molecular Sciences Laboratory , Pacific Northwest National Laboratory , Richland , Washington 99352 , United States
| | - Leonard J Mueller
- Department of Chemistry , University of California-Riverside , Riverside , California 92501 , United States
| | - Cynthia K Larive
- Department of Chemistry , University of California-Riverside , Riverside , California 92501 , United States
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6
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Brown GD, Bauer J, Osborn HMI, Kuemmerle R. A Solution NMR Approach To Determine the Chemical Structures of Carbohydrates Using the Hydroxyl Groups as Starting Points. ACS OMEGA 2018; 3:17957-17975. [PMID: 31458388 PMCID: PMC6644132 DOI: 10.1021/acsomega.8b02136] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/22/2018] [Accepted: 12/07/2018] [Indexed: 06/10/2023]
Abstract
An efficient NMR approach is described for determining the chemical structures of the monosaccharide glucose and four disaccharides, namely, nigerose, gentiobiose, leucrose and isomaltulose. This approach uses the 1H resonances of the -OH groups, which are observable in the NMR spectrum of a supercooled aqueous solution, as the starting point for further analysis. The 2D-NMR technique, HSQC-TOCSY, is then applied to fully define the covalent structure (i.e., the topological relationship between C-C, C-H, and O-H bonds) that must be established for a novel carbohydrate before proceeding to further conformational studies. This process also leads to complete assignment of all 1H and 13C resonances. The approach is exemplified by analyzing the monosaccharide glucose, which is treated as if it were an "unknown", and also by fully assigning all the NMR resonances for the four disaccharides that contain glucose. It is proposed that this technique should be equally applicable to the determination of chemical structures for larger carbohydrates of unknown composition, including those that are only available in limited quantities from biological studies. The advantages of commencing the structure elucidation of a carbohydrate at the -OH groups are discussed with reference to the now well-established 2D-/3D-NMR strategy for investigation of peptides/proteins, which employs the -NH resonances as the starting point.
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Affiliation(s)
- Geoffrey D. Brown
- Department of Chemistry and Reading School of Pharmacy, The University of Reading, Whiteknights, Reading RG6 6AP, United Kingdom
| | - Julia Bauer
- Department of Chemistry and Reading School of Pharmacy, The University of Reading, Whiteknights, Reading RG6 6AP, United Kingdom
| | - Helen M. I. Osborn
- Department of Chemistry and Reading School of Pharmacy, The University of Reading, Whiteknights, Reading RG6 6AP, United Kingdom
| | - Rainer Kuemmerle
- Bruker
Biospin AG, NMR Division, Industriestrasse 26, CH-8117 Fallanden, Switzerland
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7
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Battistel MD, Azurmendi HF, Freedberg DI. Glycan OH Exchange Rate Determination in Aqueous Solution: Seeking Evidence for Transient Hydrogen Bonds. J Phys Chem B 2017; 121:683-695. [PMID: 27995788 DOI: 10.1021/acs.jpcb.6b10594] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Hydrogen bonds (Hbonds) are important stabilizing forces in biomolecules. However, for glycans in aqueous solution, direct NMR detection of Hbonds is elusive because of their transient nature. Here, we present Isotope-based Natural-abundance TOtal correlation eXchange SpectroscopY (INTOXSY), a new 1H-13C heteronuclear single quantum coherence-total correlation spectroscopy based method, to extract OH groups' exchange rate constants (kex) for molecules in natural 13C abundance and show that OH Hbonds can be inferred from "slower" H/D kex. We evaluate kex measured with INTOXSY in light of those extracted with line-shape analysis. Subsequently, we use a set of common glycans to establish a kex reference basis set and to infer the existence of transient Hbonds involving OH donor groups. Then, we report kex values for a series of mono- and disaccharides, as well as for oligosaccharides sialyl Lewis X and β-cyclodextrin, and compare the results with those from the reference set to extract Hbond information. Finally, we utilize NMR experimental data in conjunction with molecular dynamics simulations to establish donor and acceptor Hbond pairs. Our exchange rate measurements indicate that OH/OD exchange rates, kHD, values <10 s-1 are consistent with transient Hbond OH groups and potential acceptor groups can be uncovered through MD simulations.
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Affiliation(s)
- Marcos D Battistel
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration , 10903 New Hampshire Avenue, Silver Spring, Maryland 20903, United States
| | - Hugo F Azurmendi
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration , 10903 New Hampshire Avenue, Silver Spring, Maryland 20903, United States
| | - Darón I Freedberg
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration , 10903 New Hampshire Avenue, Silver Spring, Maryland 20903, United States
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8
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Fontana C, Kovacs H, Widmalm G. NMR structure analysis of uniformly 13C-labeled carbohydrates. JOURNAL OF BIOMOLECULAR NMR 2014; 59:95-110. [PMID: 24771296 DOI: 10.1007/s10858-014-9830-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Accepted: 04/16/2014] [Indexed: 05/26/2023]
Abstract
In this study, a set of nuclear magnetic resonance experiments, some of them commonly used in the study of (13)C-labeled proteins and/or nucleic acids, is applied for the structure determination of uniformly (13)C-enriched carbohydrates. Two model substances were employed: one compound of low molecular weight [(UL-(13)C)-sucrose, 342 Da] and one compound of medium molecular weight ((13)C-enriched O-antigenic polysaccharide isolated from Escherichia coli O142, ~10 kDa). The first step in this approach involves the assignment of the carbon resonances in each monosaccharide spin system using the anomeric carbon signal as the starting point. The (13)C resonances are traced using (13)C-(13)C correlations from homonuclear experiments, such as (H)CC-CT-COSY, (H)CC-NOESY, CC-CT-TOCSY and/or virtually decoupled (H)CC-TOCSY. Based on the assignment of the (13)C resonances, the (1)H chemical shifts are derived in a straightforward manner using one-bond (1)H-(13)C correlations from heteronuclear experiments (HC-CT-HSQC). In order to avoid the (1) J CC splitting of the (13)C resonances and to improve the resolution, either constant-time (CT) in the indirect dimension or virtual decoupling in the direct dimension were used. The monosaccharide sequence and linkage positions in oligosaccharides were determined using either (13)C or (1)H detected experiments, namely CC-CT-COSY, band-selective (H)CC-TOCSY, HC-CT-HSQC-NOESY or long-range HC-CT-HSQC. However, due to the short T2 relaxation time associated with larger polysaccharides, the sequential information in the O-antigen polysaccharide from E. coli O142 could only be elucidated using the (1)H-detected experiments. Exchanging protons of hydroxyl groups and N-acetyl amides in the (13)C-enriched polysaccharide were assigned by using HC-H2BC spectra. The assignment of the N-acetyl groups with (15)N at natural abundance was completed by using HN-SOFAST-HMQC, HNCA, HNCO and (13)C-detected (H)CACO spectra.
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Affiliation(s)
- Carolina Fontana
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
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9
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Soltesova M, Kowalewski J, Widmalm G. Dynamics of exocyclic groups in the Escherichia coli O91 O-antigen polysaccharide in solution studied by carbon-13 NMR relaxation. JOURNAL OF BIOMOLECULAR NMR 2013; 57:37-45. [PMID: 23897032 DOI: 10.1007/s10858-013-9763-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Accepted: 07/17/2013] [Indexed: 06/02/2023]
Abstract
Carbon-13 relaxation data are reported for exocyclic groups of hexopyranosyl sugar residues in the repeating unit within the Escherichia coli O91 O-antigen polysaccharide in a dilute D2O solution. The measurements of T 1, T 2 and heteronuclear nuclear Overhauser enhancements were carried out at 310 K at two magnetic fields (16.4 T, 21.1 T). The data were analyzed using the standard and extended Lipari-Szabo models, as well as a conformational jump model. The extended version of the Lipari-Szabo and the two-site jump models were most successful for the hydroxymethyl groups of Gal and GlcNAc sugar residues. Different dynamics was found for the hydroxymethyl groups associated with different configurations (D-gluco, D-galacto) of the sugar residues, the latter being faster than the former.
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Affiliation(s)
- Maria Soltesova
- Arrhenius Laboratory, Department of Materials and Environmental Chemistry, Stockholm University, 106 91, Stockholm, Sweden
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10
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Battistel MD, Pendrill R, Widmalm G, Freedberg DI. Direct Evidence for Hydrogen Bonding in Glycans: A Combined NMR and Molecular Dynamics Study. J Phys Chem B 2013; 117:4860-9. [DOI: 10.1021/jp400402b] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Marcos D. Battistel
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration, 1401 Rockville Pike, Rockville, Maryland 20852-1448, United States
| | - Robert Pendrill
- Department of Organic Chemistry,
Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
| | - Göran Widmalm
- Department of Organic Chemistry,
Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
| | - Darón I. Freedberg
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration, 1401 Rockville Pike, Rockville, Maryland 20852-1448, United States
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11
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Widmalm G. A perspective on the primary and three-dimensional structures of carbohydrates. Carbohydr Res 2013; 378:123-32. [PMID: 23522728 DOI: 10.1016/j.carres.2013.02.005] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 02/13/2013] [Indexed: 10/27/2022]
Abstract
Carbohydrates, in more biologically oriented areas referred to as glycans, constitute one of the four groups of biomolecules. The glycans, often present as glycoproteins or glycolipids, form highly complex structures. In mammals ten monosaccharides are utilized in building glycoconjugates in the form of oligo- (up to about a dozen monomers) and polysaccharides. Subsequent modifications and additions create a large number of different compounds. In bacteria, more than a hundred monosaccharides have been reported to be constituents of lipopolysaccharides, capsular polysaccharides, and exopolysaccharides. Thus, the number of polysaccharide structures possible to create is huge. NMR spectroscopy plays an essential part in elucidating the primary structure, that is, monosaccharide identity and ring size, anomeric configuration, linkage position, and sequence, of the sugar residues. The structural studies may also employ computational approaches for NMR chemical shift predictions (CASPER program). Once the components and sequence of sugar residues have been unraveled, the three-dimensional arrangement of the sugar residues relative to each other (conformation), their flexibility (transitions between and populations of conformational states), together with the dynamics (timescales) should be addressed. To shed light on these aspects we have utilized a combination of experimental liquid state NMR techniques together with molecular dynamics simulations. For the latter a molecular mechanics force field such as our CHARMM-based PARM22/SU01 has been used. The experimental NMR parameters acquired are typically (1)H,(1)H cross-relaxation rates (related to NOEs), (3)JCH and (3)JCCtrans-glycosidic coupling constants and (1)H,(13)C- and (1)H,(1)H-residual dipolar couplings. At a glycosidic linkage two torsion angles ϕ and ψ are defined and for 6-substituted residues also the ω torsion angle is required. Major conformers can be identified for which highly populated states are present. Thus, in many cases a well-defined albeit not rigid structure can be identified. However, on longer timescales, oligosaccharides must be considered as highly flexible molecules since also anti-conformations have been shown to exist with H-C-O-C torsion angles of ∼180°, compared to syn-conformations in which the protons at the carbon atoms forming the glycosidic linkage are in close proximity. The accessible conformational space governs possible interactions with proteins and both minor changes and significant alterations occur for the oligosaccharides in these interaction processes. Transferred NOE NMR experiments give information on the conformation of the glycan ligand when bound to the proteins whereas saturation transfer difference NMR experiments report on the carbohydrate part in contact with the protein. It is anticipated that the subtle differences in conformational preferences for glycan structures facilitate a means to regulate biochemical processes in different environments. Further developments in the analysis of glycan structure and in particular its role in interactions with other molecules, will lead to clarifications of the importance of structure in biochemical regulation processes essential to health and disease.
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Affiliation(s)
- Göran Widmalm
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.
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12
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Battistel MD, Shangold M, Trinh L, Shiloach J, Freedberg DI. Evidence for helical structure in a tetramer of α2-8 sialic acid: unveiling a structural antigen. J Am Chem Soc 2012; 134:10717-20. [PMID: 22703338 DOI: 10.1021/ja300624j] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Characteristic H-bonding patterns define secondary structure in proteins and nucleic acids. We show that similar patterns apply for α2-8 sialic acid (SiA) in H(2)O and that H-bonds define its structure. A (15)N,(13)C α2-8 SiA tetramer, (SiA)(4), was used as a model system for the polymer. At 263 K, we detected intra-residue through-H-bond J couplings between (15)N and C8 for residues R-I-R-III of the tetramer, indicating H-bonds between the (15)N's and the O8's of these residues. Additional J couplings between the (15)N's and C2's of the adjacent residues confirm the putative H-bonds. NH groups showing this long-range correlation also experience slower (1)H/(2)H exchange. Additionally, detection of couplings between H7 and C2 for R-II and R-III implies that the conformations of the linkers between these residues are different than in the monomers. These structural elements are consistent with two left-handed helical models: 2 residues/turn (2(4) helix) and 4 residues/turn (1(4) helix). To discriminate between models, we resorted to (1)H,(1)H NOEs. The 2(4) helical model is in better agreement with the experimental data. We provide direct evidence of H-bonding for (SiA)(4) and show how H-bonds can be a determining factor for shaping its 3D structure.
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Affiliation(s)
- Marcos D Battistel
- Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration, 1401 Rockville Pike, Rockville, Maryland 20852-1448, USA
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13
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Langeslay DJ, Young RP, Beni S, Beecher CN, Mueller LJ, Larive CK. Sulfamate proton solvent exchange in heparin oligosaccharides: evidence for a persistent hydrogen bond in the antithrombin-binding pentasaccharide Arixtra. Glycobiology 2012; 22:1173-82. [PMID: 22593556 DOI: 10.1093/glycob/cws085] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Sulfamate groups (NHSO(3)(-)) are important structural elements in the glycosaminoglycans (GAGs) heparin and heparan sulfate (HS). In this work, proton nuclear magnetic resonance (NMR) line-shape analysis is used to explore the solvent exchange properties of the sulfamate NH groups within heparin-related mono-, di-, tetra- and pentasaccharides as a function of pH and temperature. The results of these experiments identified a persistent hydrogen bond within the Arixtra (fondaparinux sodium) pentasaccharide between the internal glucosamine sulfamate NH and the adjacent 3-O-sulfo group. This discovery provides new insights into the solution structure of the Arixtra pentasaccharide and suggests that 3-O-sulfation of the heparin N-sulfoglucosamine (GlcNS) residues pre-organize the secondary structure in a way that facilitates binding to antithrombin-III. NMR studies of the GlcNS NH groups can provide important information about heparin structure complementary to that available from NMR spectral analysis of the carbon-bound protons.
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Affiliation(s)
- Derek J Langeslay
- Department of Chemistry, University of California-Riverside, Riverside, CA 92521, USA
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