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  • 1. Both, P.
    et al.
    Green, A. P.
    Gray, C. J.
    Sardzik, R.
    Voglmeir, J.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Austeri, M.
    Rejzek, M.
    Richardson, D.
    Field, R. A.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Flitsch, S. L.
    Eyers, C. E.
    Discrimination of epimeric glycans and glycopeptides using IM-MS and its potential for carbohydrate sequencing2014In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 6, no 1, p. 65-74Article in journal (Refereed)
    Abstract [en]

    Mass spectrometry is the primary analytical technique used to characterize the complex oligosaccharides that decorate cell surfaces. Monosaccharide building blocks are often simple epimers, which when combined produce diastereomeric glycoconjugates indistinguishable by mass spectrometry. Structure elucidation frequently relies on assumptions that biosynthetic pathways are highly conserved. Here, we show that biosynthetic enzymes can display unexpected promiscuity, with human glycosyltransferase pp-a-GanT2 able to utilize both uridine diphosphate N-acetylglucosamine and uridine diphosphate N-acetylgalactosamine, leading to the synthesis of epimeric glycopeptides in vitro. Ion-mobility mass spectrometry ( IM-MS) was used to separate these structures and, significantly, enabled characterization of the attached glycan based on the drift times of the monosaccharide product ions generated following collision-induced dissociation. Finally, ion-mobility mass spectrometry following fragmentation was used to determine the nature of both the reducing and non-reducing glycans of a series of epimeric disaccharides and the branched pentasaccharide Man3 glycan, demonstrating that this technique may prove useful for the sequencing of complex oligosaccharides.

  • 2. Chassagne, Pierre
    et al.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Guerreiro, Catherine
    Gauthier, Charles
    Phalipon, Armelle
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mulard, Laurence A.
    Structural Studies of the O-Acetyl-Containing O-Antigen from a Shigella flexneri Serotype 6 Strain and Synthesis of Oligosaccharide Fragments Thereof2013In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 19, p. 4085-4106Article in journal (Refereed)
    Abstract [en]

    Extensive analysis by NMR spectroscopy of the delipidated lipopolysaccharide of Shigella flexneri serotype 6 strain MDC 2924-71 confirmed the most recently reported structure of the O-antigen repeating unit as {4)--D-GalpA-(13)--D-GalpNAc-(12)--L-Rhap3Ac/4Ac-(12)--L-Rhap-(1}, and revealed the non-stoichiometric acetylation at O-3C/4C. Input from the CASPER program helped to ascertain the fine distribution of the three possible patterns of O-acetylation. The non-O-acetylated repeating unit (ABCD) corresponded to about 2/3 of the population, while 1/4 was acetylated at O-3C (3AcCDAB), and 1/10 at O-4C (4AcCDAB). Di- to tetrasaccharides with a GalpA residue (A) at their reducing end were synthesized as their propyl glycosides following a multistep linear strategy relying on late-stage acetylation at O-3C. Thus, the 3C-O-acetylated and non-O-acetylated targets were synthesized from common protected intermediates. Rhamnosylation was most efficiently achieved by using imidate donors, including at O-4 of a benzyl galacturonate acceptor. In contrast, a thiophenyl 2-deoxy-2-trichloroacetamido-D-galactopyranoside precursor was preferred for chain elongation involving residue B. Final Pd/C-mediated deprotection ensured O-acetyl stability. All of the target molecules represent parts of the O-antigen of S. flexneri 6, a prevalent serotype. Non-O-acetylated oligosaccharides are also fragments of the Escherichia coli O147 O-antigen.

  • 3.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    NMR spectroscopy in structural and conformational analysis of bacterial polysaccharides2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carbohydrates constitute one of the three major classes of biomolecules found in all living cells and, unlike nucleic acids and proteins, their polymeric structures are not based on a template. The structural diversity of these molecules confers them an enormous capacity to encode information in biological systems, acting as efficient mediators in the interaction of the cell with the environment. In order to understand the roles of glycans in biological processes it is of key importance to have a detailed understanding of their structures and conformational preferences, and NMR spectroscopy is one of most powerful techniques for the study of these molecules in solution.

    This thesis is focused on the structural and conformational analysis of lipopolysaccharides from Gram-negative bacteria. In the first two projects (Chapter 2 and 3) the structural analyses of the biological repeating units of the O-antigen polysaccharides from E. coli O174ab and O115 are described; in both cases a combination of NMR spectroscopy and gas chromatography techniques were used. Special emphasis was made in the characterization of the O-acetylation patterns observed in the native O-antigen polysaccharide from E. coli O115. Chapter 4 describes the development of a new methodology for the determination of the absolute configuration of monosaccharide components of glycans. This methodology was used in the structural elucidation of the O-antigen PS of E. coli O155 (Chapter 5) that was carried out in a semi-automated manner using the program CASPER and unassigned NMR data. The conformational preferences of O-antigen PS of E. coli O5ac and O5ab are analyzed in Chapter 6, using a combination of NMR spectroscopy and molecular modeling methods. In Chapter 7 the structural analysis is focused on the core region of the LPS, and the structures of the deacylated lipooligosaccharides of three rough mutants of B. melitesis are reported. In several of the aforementioned chapters, the biosynthetic aspects behind the assembly of the respective PSs were examined on the bases of genetic information available in the NCBI and ECODAB databases.  Finally, in Chapter 8, different NMR pulse sequences available for the study of proteins and nucleic acids were evaluated and optimized for the structural analysis of 13C uniformly-labeled oligo- and polysaccharides.

  • 4.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural studies of glycans by NMR spectroscopy2012Licentiate thesis, comprehensive summary (Other academic)
  • 5.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Conde-Alvarez, Raquel
    Ståhle, Jonas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Holst, Otto
    Iriarte, Maite
    Zhao, Yun
    Arce-Gorvel, Vilma
    Hanniffy, Sean
    Gorvel, Jean-Pierre
    Moriyon, Ignacio
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural Studies of Lipopolysaccharide-defective Mutants from Brucella melitensis Identify a Core Oligosaccharide Critical in Virulence2016In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 291, no 14, p. 7727-7741Article in journal (Refereed)
    Abstract [en]

    The structures of the lipooligosaccharides from Brucella melitensis mutants affected in the WbkD and ManB(core) proteins have been fully characterized using NMR spectroscopy. The results revealed that disruption of wbkD gives rise to a rough lipopolysaccharide (R-LPS) with a complete core structure (beta-D-Glcp-(1 -> 4)-alpha-Kdop-(2 -> 4)[beta-D-GlcpN-(1 -> 6)-beta-D-GlcpN-(1 -> 4)[beta-D-GlcpN-(1 -> 6)]-beta-D-GlcpN-(1 -> 3)-alpha-D-Manp-(1 -> 5)]-alpha-Kdop-(2 -> 6)-beta-D-GlcpN3N4P-(1 -> 6)-alpha-D-GlcpN3N1P), in addition to components lacking one of the terminal beta-D-GlcpN and/or the beta-D-Glcp residues (48 and 17%, respectively). These structures were identical to those of the R-LPS from B. melitensis EP, a strain simultaneously expressing both smooth and R-LPS, also studied herein. In contrast, disruption of man-B-core gives rise to a deep-rough pentasaccharide core (beta-D-Glcp-(1 -> 4)-alpha-Kdop-(2 -> 4)-alpha-Kdop-(2 -> 6)-beta-D-GlcpN3N4P-(1 -> 6)-alpha-D-GlcpN3N1P) as the major component (63%), as well as a minor tetrasaccharide component lacking the terminal beta-D-Glcp residue (37%). These results are in agreement with the predicted functions of the WbkD (glycosyltransferase involved in the biosynthesis of the O-antigen) and ManB(core) proteins (phosphomannomutase involved in the biosynthesis of a mannosyl precursor needed for the biosynthesis of the core and O-antigen). We also report that deletion of B. melitensis wadC removes the core oligosaccharide branch not linked to the O-antigen causing an increase in overall negative charge of the remaining LPS inner section. This is in agreement with the mannosyltransferase role predicted for WadC and the lack of GlcpN residues in the defective core oligosaccharide. Despite carrying the O-antigen essential in B. melitensis virulence, the core deficiency in the wadC mutant structure resulted in a more efficient detection by innate immunity and attenuation, proving the role of the beta-D-GlcpN-(1 -> 6)-beta-D-GlcpN-(1 -> 4)[beta-D-GlcpN-(1 -> 6)]-beta-D-GlcpN-(1 -> 3)-alpha-D-Manp-(1 -> 5) structure in virulence.

  • 6.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Holst, Otto
    Moriyón, Ignacio
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural studies of the rough lipopolysaccharides of Brucella melitensis mutants affected in the biosynthesis of the core and O-antigen polysaccharideManuscript (preprint) (Other academic)
  • 7.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kovacs, Helena
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    NMR structure analysis of uniformly 13C-labeled carbohydrates2014In: Journal of Biomolecular NMR, ISSN 0925-2738, E-ISSN 1573-5001, Vol. 59, no 2, p. 95-110Article in journal (Refereed)
    Abstract [en]

    In this study, a set of nuclear magnetic resonance experiments, some of them commonly used in the study of C-13-labeled proteins and/or nucleic acids, is applied for the structure determination of uniformly C-13-enriched carbohydrates. Two model substances were employed: one compound of low molecular weight [(UL-C-13)-sucrose, 342 Da] and one compound of medium molecular weight (C-13-enriched O-antigenic polysaccharide isolated from Escherichia coli O142, similar to 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 C-13 resonances are traced using C-13-C-13 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 C-13 resonances, the H-1 chemical shifts are derived in a straightforward manner using one-bond H-1-C-13 correlations from heteronuclear experiments (HC-CT-HSQC). In order to avoid the (1) J (CC) splitting of the C-13 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 C-13 or H-1 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 T-2 relaxation time associated with larger polysaccharides, the sequential information in the O-antigen polysaccharide from E. coli O142 could only be elucidated using the H-1-detected experiments. Exchanging protons of hydroxyl groups and N-acetyl amides in the C-13-enriched polysaccharide were assigned by using HC-H2BC spectra. The assignment of the N-acetyl groups with N-15 at natural abundance was completed by using HN-SOFAST-HMQC, HNCA, HNCO and C-13-detected (H)CACO spectra.

  • 8.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Li, Shengyu
    Yang, Zhennai
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural studies of the exopolysaccharide from Lactobacillus plantarum C88 using NMR spectroscopy and the program CASPER2015In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 402, p. 87-94Article in journal (Refereed)
    Abstract [en]

    Some lactic acid bacteria, such as those of the Lactobacillus genus, have the ability to produce exopolysaccharides (EPSs) that confer favorable physicochemical properties to food and/or beneficial physiological effects on human health. In particular, the EPS of Lactobacillus plantarum C88 has recently demonstrated in vitro antioxidant activity and, herein, its structure has been investigated using NMR spectroscopy and the computer program CASPER (Computer Assisted Spectrum Evaluation of Regular polysaccharides). The pentasaccharide repeating unit of the O-deacetylated EPS consists of a trisaccharide backbone, -> 4)-alpha-DGalp-(1 -> 2)-alpha-D-Glcp-(1 -> 3)-beta-D-Glcp-(1 ->, with terminal D-Glc and D-Gal residues (1.0 and 0.8 equiv per repeating unit, respectively) extending from O3 and O6, respectively, of the -> 4)-alpha-D-Galp-(1 -> residue. In the native EPS an O-acetyl group is present, 0.85 equiv per repeating unit, at O2 of the alpha-linked galactose residue; thus the repeating unit of the EPS has the following structure: -> 4)[beta-D-Glcp-(1 -> 3)][beta-D-Galp-(1 -> 6)]alpha-D-Galp2Ac-(1 -> 2)-alpha-D-Glcp-(1 -> 3)-beta-D-Glcp-(1 ->. These structural features, and the chain length (similar to 10(3) repeating units on average, determined in a previous study), are expected to play an important role in defining the physicochemical properties of the polymer.

  • 9.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lundborg, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Weintraub, Andrej
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Rapid structural elucidation of polysaccharides employing predicted functions of glycosyltransferases and NMR data: Application to the O-antigen of Escherichia coli O592014In: Glycobiology, ISSN 0959-6658, E-ISSN 1460-2423, Vol. 24, no 5, p. 450-457Article in journal (Refereed)
    Abstract [en]

    A computerized method that uses predicted functions of glycosyltransferases (GTs) in conjunction with unassigned NMR data has been developed for the structural elucidation of bacterial polysaccharides (PSs). In this approach, information about the action of GTs (consisting of possible sugar residues used as donors and/or acceptors, as well as the anomeric configuration and/or substitution position in the respective glycosidic linkages) is extracted from the Escherichia coli O-antigen database and is submitted, together with the unassigned NMR data, to the CASPER program. This time saving methodology, which alleviates the need for chemical analysis, was successfully implemented in the structural elucidation of the O-antigen PS of E. coli O59. The repeating unit of the O-specific chain was determined using the O-deacylated PS and has a branched structure, namely, -> 6)[alpha-d-GalpA3Ac/4Ac-(1 -> 3)]-alpha-d-Manp-(1 -> 3)-alpha-d-Manp-(1 -> 3)-beta-d-Manp-(1 -> 3)-alpha-d-GlcpNAc-(1 ->. The identification of the O-acetylation positions was efficiently performed by comparison of the H-1,C-13 HSQC NMR spectra of the O-deacylated lipopolysaccharide and the lipid-free PS in conjunction with chemical shift predictions made by the CASPER program. The side-chain d-GalpA residue carries one equivalent of O-acetyl groups at the O-3 and O-4 positions distributed in the LPS in a 3:7 ratio, respectively. The presence of O-acetyl groups in the repeating unit of the E. coli O59 PS is consistent with the previously proposed acetyltransferase WclD in the O-antigen gene cluster.

  • 10.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lundborg, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Weintraub, Andrej
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural studies and biosynthetic aspects of the o antigen polysaccharide from Escherichia coli o1742012In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 354, p. 102-105Article in journal (Refereed)
    Abstract [en]

    The structure of the repeating unit of the O-antigenic polysaccharide (PS) from Escherichia coli O174 has been determined. Component analysis together with H-1 and C-13 NMR spectroscopy experiments were employed to elucidate the structure. Inter-residue correlations were determined by H-1, C-13-heteronuclear multiple-bond correlation and H-1, H-1-NOESY experiments. The PS is composed of tetrasaccharide repeating units with the following structure: -> 4)-beta-D-GlcpA-(1 -> 3)-beta-D-Galp-(1 -> 3)-beta-D-GalpNAc-(1 -> vertical bar beta-D-GlcpNAc-(1 -> 2) Cross-peaks of low intensity were present in the NMR spectra consistent with a beta-D-GlcpNAc-(1 -> 2)-beta-D-GlcpA(1 -> structural element at the terminal part of the polysaccharide, which on average is composed of similar to 15 repeating units. Consequently the biological repeating unit has a 3-substituted N-acetyl-D-galactosamine residue at its reducing end.

  • 11.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ramström, Kristoffer
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Weintraub, Andrej
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural studies of the O-antigen polysaccharide from Escherichia coli O115 and biosynthetic aspects thereof2013In: Glycobiology, ISSN 0959-6658, E-ISSN 1460-2423, Vol. 23, no 3, p. 354-362Article in journal (Refereed)
    Abstract [en]

    The structure of the O-antigen polysaccharide (PS) of Escherichia coliO115 has been investigated using a combination of component analysis and 1D and 2D nuclear magnetic resonance (NMR) spectroscopy experiments. The repeating unit of the O-antigen was elucidated using the O-deacetylated PS and has the following branched pentasaccharide structure: →3)[β-L-Rhap-(1 → 4)]-β-D-GlcpNAc-(1 → 4)-α-D-GalpA-(1 → 3)-α-D-Manp-(1 → 3)-β-D-GlcpNAc-(1→. Cross-peaks of low intensity, corresponding to a β-L-Rhap-(1 → 4)-β-D-GlcpNAc-(1→ structural element, were present in the NMR spectra and attributed to the terminal part of the PS; this information defines the biological repeating unit of the O-antigen by having a 3-substituted N-acetyl-D-glucosamine (GlcNAc) residue at its reducing end. Analysis of the NMR spectra of the native PS revealed O-acetyl groups distributed over different positions of theL-Rhap residue (∼0.70 per repeating unit) as well as at O-2 and O-3 of the D-GalpA residue (∼0.03 and ∼0.25 per repeating unit, respectively), which is in agreement with the presence of two acetyltransferases previously identified in the O-antigen gene cluster (Wang Q, Ruan X, Wei D, Hu Z, Wu L, Yu T, Feng L, Wang L. 2010. Mol Cell Probes. 24:286–290.). In addition, the four glycosyltransferases initially identified in the O-antigen gene cluster of E. coli O115 were analyzed using BLAST, and the function of two of them predicted on the basis of similarities with glycosyltransferases from Shigella dysenteriae type 5 and 12, as well as E. coli O58 and O152.

  • 12.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Weintraub, Andrej
    Karolinska Institute.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Facile Structural Elucidation of Glycans Using NMR Spectroscopy Data and the Program CASPER: Application to the O-Antigen Polysaccharide of Escherichia coli O1552013In: ChemPlusChem, ISSN 2192-6506, Vol. 78, no 11, p. 1327-1329Article in journal (Refereed)
    Abstract [en]

    The program CASPER was successfully employed to rapidly elucidate a new O-antigen polysaccharide structure (obtained from a strain of Escherichia coli serogroup O155), using solelyunassigned NMR spectroscopy data as input information. Thus, what is considered the most tedious and time-consuming part of the structural elucidation process has been reduced from several hours (or even days) of manual interpretation to about four minutes of automated analysis.

  • 13.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Weintraub, Andrej
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural Elucidation of the O-Antigen Polysaccharide from Escherichia coli O1812015In: ChemistryOpen, ISSN 2191-1363, Vol. 4, no 1, p. 47-55Article in journal (Refereed)
    Abstract [en]

    Shiga-toxin-producing Escherichia coli (STEC) is an important pathogen associated to food-borne infection in humans; strains of E.coli O181, isolated from human cases of diarrhea, have been classified as belonging to this pathotype. Herein, the structure of the O-antigen polysaccharide (PS) from E.coli O181 has been investigated. The sugar analysis showed quinovosamine (QuiN), glucosamine (GlcN), galactosamine (GalN), and glucose (Glc) as major components. Analysis of the high-resolution mass spectrum of the oligosaccharide (OS), obtained by dephosphorylation of the O-deacetylated PS with aqueous 48% hydrofluoric acid, revealed a pentasaccharide composed of two QuiNAc, one GlcNAc, one GalNAc, and one Glc residue. The H-1 and (CNMR)-C-13 chemical shift assignments of the OS were carried out using 1D and 2D NMR experiments, and the OS was sequenced using a combination of tandem mass spectrometry (MS/MS) data and NMR (CNMR)-C-13 glycosylation shifts. The structure of the native PS was determined using NMR spectroscopy, and it consists of branched pentasaccharide repeating units joined by phosphodiester linkages: -> 4)[alpha-L-QuipNAc-(1 -> 3)]-alpha-D-GalpNAc6Ac-(1 -> 6)-alpha-D-Glcp-(1 -> P-4)-alpha-L-QuipNAc-(1 -> 3)-beta-D-GlcpNAc-(1 ->; the O-acetyl groups represent 0.4 equivalents per repeating unit. Both the OS and PSs exhibit rare conformational behavior since two of the five anomeric proton resonances could only be observed at an elevated temperature.

  • 14.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Weintraub, Andrej
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural studies and biosynthetic aspects of the O-antigen polysaccharide from Escherichia coli O422015In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 403, p. 174-181Article in journal (Refereed)
    Abstract [en]

    The structure of the O-antigen polysaccharide (PS) from Escherichia coli O42 has been investigated by NMR spectroscopy as the main method, which was complemented with sugar analysis, mass spectrometry, and analysis of biosynthetic information. The O-specific chain of the O-deacylated lipopolysaccharide (LPS-OH) consists of branched tetrasaccharide-glycerol repeating units joined by phosphodiester linkages. The lipid-free polysaccharide contains 0.8 equiv of O-acetyl groups per repeating unit and has the following teichoic acid-like structure: Based on biosynthetic aspects, this should also be the biological repeating unit. This O-antigen structure is remarkably similar to that of E. coli O28ac, differing only in the presence or absence, respectively, of a glucose residue at the branching point. The structural similarity explains the serological cross-reactivity observed between strains of these two serogroups, and also their almost identical O-antigen gene cluster sequences. -> 2)-(R)-Gro-(1-P-4)-beta-D-GlcpNAc-(1 -> 3)-beta-D-Galf2Ac-(1 -> 3)-alpha-D-GlcpNAc-(1 -> vertical bar a-D-Glcp-(1 -> 3)

  • 15.
    Fontana, Carolina
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zaccheus, Mona V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Weintraub, Andrej
    Ansaruzzaman, Mohammad
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural studies of a polysaccharide from Vibrio parahaemolyticus strain AN-160002016In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 432, p. 41-49Article in journal (Refereed)
    Abstract [en]

    The structure of a polysaccharide from Vibrio parahaemolyticus strain AN-16000 has been investigated. The sugar and absolute configuration analysis revealed D-Glc, D-GalN, D-QuiN and L-FucN as major components. The PS was subjected to dephosphorylation with aqueous 40% HF to obtain an oligosaccharide that was analyzed by H-1 and C-13 NMR spectroscopy. The HR-MS spectrum of the oligosaccharide revealed a pentasaccharide composed of two Glc residues, one QuiNAc and one GalNAc, one FucNAc, as well as a glycerol moiety. The structure of the PS was determined using H-1, C-13, N-15 and P-31 NMR spectroscopy; inter-residue correlations were identified by H-1, C-13-heteronuclear multiple-bond correlation, H-1, H-1-NOESY and H-1, P-31-hetero-TOCSY experiments. The PS backbone has the following teichoic acid-like structure: -> 3)-D-Gro-(1-P-6)-beta-D-Glcp-(1 -> 4)-alpha-L-FucpNAc-(1 -> 3)-beta-D-QuipNAc-(1 -> with a side-chain consisting of alpha-D-Glcp-(1 -> 6)-alpha-D-GalpNAc-(1 -> linked to the O3 position of the FucNAc residue.

  • 16.
    Lundborg, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Automatic structure determination of regular polysaccharides based solely on NMR spectroscopy2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 11, p. 3851-3855Article in journal (Refereed)
    Abstract [en]

    The structural analysis of polysaccharides requires that the sugar components and their absolute configurations are determined. We here show that this can be performed based on NMR spectroscopy by utilizing butanolysis with (+)- and (-)-2-butanol that gives the corresponding 2-butyl glycosides with characteristic 1H and 13C NMR chemical shifts. The subsequent computer-assisted structural determination by CASPER can then be based solely on NMR data in a fully automatic way as shown and implemented herein. The method is additionally advantageous in that reference data only have to be prepared once and from a user's point of view only the unknown sample has to be derivatized for use in CASPER.

  • 17. Mally, Manuela
    et al.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    LeibundGut-Landmann, Salome
    Laacisse, Lamia
    Fan, Yao-Yun
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Aebi, Markus
    Glycoengineering of host mimicking type-2 LacNAc polymersand Lewis X antigens on bacterial cell surfaces2013In: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 87, no 1, p. 112-131Article in journal (Refereed)
    Abstract [en]

    Bacterial carbohydrate structures play a central role in mediating a variety of host-pathogen interactions. Glycans can either elicit protective immune response or lead to escape of immune surveillance by mimicking host structures. Lipopolysaccharide (LPS), a major component on the surface of Gram-negative bacteria, is composed of a lipid A-core and the O-antigen polysaccharide. Pathogens like Neisseria meningitidis expose a lipooligosaccharide (LOS), which outermost glycans mimick mammalian epitopes to avoid immune recognition. Lewis X (Gal beta 1-4(Fuc alpha 1-3)GlcNAc) antigens of Helicobacter pylori or of the helminth Schistosoma mansoni modulate the immune response by interacting with receptors on human dendritic cells. In a glycoengineering approach we generate human carbohydrate structures on the surface of recombinant Gram-negative bacteria, such as Escherichia coli and Salmonella enterica sv. Typhimurium that lack O-antigen. A ubiquitous building block in mammalian N-linked protein glycans is Gal beta 1-4GlcNAc, referred to as a type-2 N-acetyllactosamine, LacNAc, sequence. Strains displaying polymeric LacNAc were generated by introducing a combination of glycosyltransferases that act on modified lipid A-cores, resulting in efficient expression of the carbohydrate epitope on bacterial cell surfaces. The poly-LacNAc scaffold was used as an acceptor for fucosylation leading to polymers of Lewis X antigens. We analysed the distribution of the carbohydrate epitopes by FACS, microscopy and ELISA and confirmed engineered LOS containing LacNAc and Lewis X repeats by MALDI-TOF and NMR analysis. Glycoengineered LOS induced pro-inflammatory response in murine dendritic cells. These bacterial strains can thus serve as tools to analyse the role of defined carbohydrate structures in different biological processes.

  • 18.
    Rönnols, Jerk
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hamark, Christoffer
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Angles d'Ortoli, Thibault
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Engström, Olof
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ståhle, Jonas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zaccheus, Mona V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Säwén, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hahn, Liljan E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Iqbal, Shahzad
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Complete H-1 and C-13 NMR chemical shift assignments of mono- to tetrasaccharides as basis for NMR chemical shift predictions of oligosaccharides using the computer program CASPER2013In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 380, p. 156-166Article in journal (Refereed)
    Abstract [en]

    H-1 and C-13 NMR chemical shift data are used by the computer program CASPER to predict chemical shifts of oligo- and polysaccharides. Three types of data are used, namely, those from monosaccharides, disaccharides, and trisaccharides. To improve the accuracy of these predictions we have assigned the H-1 and C-13 NMR chemical shifts of eleven monosaccharides, eleven disaccharides, twenty trisaccharides, and one tetrasaccharide; in total 43 compounds. Five of the oligosaccharides gave two distinct sets of NMR resonances due to the alpha- and beta-anomeric forms resulting in 48 H-1 and C-13 NMR chemical shift data sets. In addition, the pyranose ring forms of Neu5Ac were assigned at two temperatures, due to chemical shift displacements as a function of temperature. The H-1 NMR chemical shifts were refined using total line-shape analysis with the PERCH NMR software. H-1 and C-13 NMR chemical shift predictions were subsequently carried out by the CASPER program (http://www.casper.organ.su.se/casper/) for three branched oligosaccharides having different functional groups at their reducing ends, namely, a mannose-containing pentasaccharide, and two fucose-containing heptasaccharides having N-acetyllactosamine residues in the backbone of their structures. Good to excellent agreement was observed between predicted and experimental H-1 and C-13 NMR chemical shifts showing the utility of the method for structural determination or confirmation of synthesized oligosaccharides.

  • 19. Sardzik, Robert
    et al.
    Green, Anthony P.
    Laurent, Nicolas
    Both, Peter
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Voglmeir, Josef
    Weissenborn, Martin J.
    Haddoub, Rose
    Grassi, Paola
    Haslam, Stuart M.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Flitsch, Sabine L.
    Chemoenzymatic Synthesis of O-Mannosylpeptides in Solution and on Solid Phase2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 10, p. 4521-4524Article in journal (Refereed)
    Abstract [en]

    O-Mannosyl glycans are known to play an important role in regulating the function of alpha-dystroglycan (alpha-DG), as defective glycosylation is associated with various phenotypes of congenital muscular dystrophy. Despite the well-established biological significance of these glycans, questions regarding their precise molecular function remain unanswered. Further biological investigation will require synthetic methods for the generation of pure samples of homogeneous glycopeptides with diverse sequences. Here we describe the first total syntheses of glycopeptides containing the tetrasaccharide NeuNAc alpha 2-3Gal beta 1-4GlcNAc beta 1-2Man alpha, which is reported to be the most abundant O-mannosyl glycan on alpha-DG. Our approach is based on biomimetic stepwise assembly from the reducing end and also gives access to the naturally occurring mono-, di-, and trisaccharide substructures. In addition to the total synthesis, we have developed a one-pot enzymatic cascade leading to the rapid synthesis of the target tetrasaccharide. Finally, solid-phase synthesis of the desired glycopeptides directly on a gold microarray platform is described.

  • 20. Sarkar, Anita
    et al.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Imberty, Anne
    Perez, Serge
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Conformational Preferences of the O-Antigen Polysaccharides of Escherichia coli O5ac and O5ab Using NMR Spectroscopy and Molecular Modeling2013In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 7, p. 2215-2224Article in journal (Refereed)
    Abstract [en]

    Escherichia coli serogroup O5 comprises two different subgroups (O5ab and O5ac), which are indiscernible from the point of view of standard immunological serotyping. The structural similarities between the O-antigen polysaccharides (PSs) of these two strains are remarkable, with the only difference being the glycosidic linkage connecting the biological tetrasaccharide repeating units. In the present study, a combination of NMR spectroscopy and molecular modeling methods were used to elucidate the conformational preferences of these two PSs. The NMR study was based on the analysis of intra- and inter-residue proton-proton distances using NOE build-up curves. Molecular models of the repeating units and their extension to polysaccharides were obtained, taking into account the conformational flexibility as assessed by the force field applied and a genetic algorithm. The agreements between experimentally measured and calculated distances could only be obtained by considering an averaging of several low energy conformations observed in the molecular models.

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