1
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Dorst KM, Widmalm G. NMR chemical shift prediction and structural elucidation of linker-containing oligo- and polysaccharides using the computer program CASPER. Carbohydr Res 2023; 533:108937. [PMID: 37734222 DOI: 10.1016/j.carres.2023.108937] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Revised: 09/01/2023] [Accepted: 09/01/2023] [Indexed: 09/23/2023]
Abstract
Carbohydrate structures containing alkyl groups as aglycones are useful for investigating enzyme activity and glycan-protein interactions. Moreover, linker-containing oligosaccharides with a spacer group are commonly used to print glycan microarrays or to prepare protein-conjugates as vaccine candidates. The structural accuracy of these synthesized glycans are essential for interpretation of results from biological experiments in which the compounds have been used and NMR spectroscopy can unravel and confirm their structures. An approach for efficient 1H and 13C NMR chemical shift assignments employed a parallel NOAH-10 measurement followed by NMR spin-simulation to refine the 1H NMR chemical shifts, as exemplified for a disaccharide with an azidoethyl group as an aglycone, the NMR chemical shifts of which have been used to enhance the quality of CASPER (http://www.casper.organ.su.se/casper/). The CASPER program has been further developed to aid characterization of linker-containing oligo- and polysaccharides, either by chemical shift prediction for comparison to experimental NMR data or as structural investigation of synthesized glycans based on acquired unassigned NMR data. The ability of CASPER to elucidate structures of linker-containing oligosaccharides is demonstrated and comparisons to assigned or unassigned NMR data show the utility of CASPER in supporting a proposed oligosaccharide structure. Prediction of NMR chemical shifts of an oligosaccharide, corresponding to the repeating unit of an O-antigen polysaccharide, having a linker as an aglycone and a non-natural substituent derivative thereof are presented to exemplify the diversity of structures handled. Furthermore, NMR chemical shift predictions of synthesized polysaccharides, corresponding to bacterial polysaccharides, containing a linker are described showing that in addition to oligosaccharide structures also polysaccharide structures having an aglycone spacer group can be analyzed by CASPER.
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Affiliation(s)
- Kevin M Dorst
- 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.
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2
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van
der Put RMF, Smitsman C, de Haan A, Hamzink M, Timmermans H, Uittenbogaard J, Westdijk J, Stork M, Ophorst O, Thouron F, Guerreiro C, Sansonetti PJ, Phalipon A, Mulard LA. The First-in-Human Synthetic Glycan-Based Conjugate Vaccine Candidate against Shigella. ACS CENTRAL SCIENCE 2022; 8:449-460. [PMID: 35559427 PMCID: PMC9088300 DOI: 10.1021/acscentsci.1c01479] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Indexed: 05/12/2023]
Abstract
Shigella, the causative agent of shigellosis, is among the main causes of diarrheal diseases with still a high morbidity in low-income countries. Relying on chemical synthesis, we implemented a multidisciplinary strategy to design SF2a-TT15, an original glycoconjugate vaccine candidate targeting Shigella flexneri 2a (SF2a). Whereas the SF2a O-antigen features nonstoichiometric O-acetylation, SF2a-TT15 is made of a synthetic 15mer oligosaccharide, corresponding to three non-O-acetylated repeats, linked at its reducing end to tetanus toxoid by means of a thiol-maleimide spacer. We report on the scale-up feasibility under GMP conditions of a high yielding bioconjugation process established to ensure a reproducible and controllable glycan/protein ratio. Preclinical and clinical batches complying with specifications from ICH guidelines, WHO recommendations for polysaccharide conjugate vaccines, and (non)compendial tests were produced. The obtained SF2a-TT15 vaccine candidate passed all toxicity-related criteria, was immunogenic in rabbits, and elicited bactericidal antibodies in mice. Remarkably, the induced IgG antibodies recognized a large panel of SF2a circulating strains. These preclinical data have paved the way forward to the first-in-human study for SF2a-TT15, demonstrating safety and immunogenicity. This contribution discloses the yet unreported feasibility of the GMP synthesis of conjugate vaccines featuring a unique homogeneous synthetic glycan hapten fine-tuned to protect against an infectious disease.
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Affiliation(s)
| | | | - Alex de Haan
- Intravacc, P.O. Box 450, 3720 AL Bilthoven, The Netherlands
| | - Martin Hamzink
- Intravacc, P.O. Box 450, 3720 AL Bilthoven, The Netherlands
| | | | | | - Janny Westdijk
- Intravacc, P.O. Box 450, 3720 AL Bilthoven, The Netherlands
| | - Michiel Stork
- Intravacc, P.O. Box 450, 3720 AL Bilthoven, The Netherlands
| | - Olga Ophorst
- Intravacc, P.O. Box 450, 3720 AL Bilthoven, The Netherlands
| | - Françoise Thouron
- Institut
Pasteur, U1202 Inserm, Unité
de Pathogénie Microbienne Moléculaire, 28 rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Catherine Guerreiro
- Institut
Pasteur, Université Paris Cité, CNRS UMR3523, Unité de Chimie des Biomolécules, 28 rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Philippe J. Sansonetti
- Institut
Pasteur, U1202 Inserm, Unité
de Pathogénie Microbienne Moléculaire, 28 rue du Dr Roux, 75724 Paris Cedex 15, France
- Chaire
de Microbiologie et Maladies Infectieuses, Collège de France, 11, place Marcelin Berthelot, 75005 Paris, France
| | - Armelle Phalipon
- Institut
Pasteur, U1202 Inserm, Unité
de Pathogénie Microbienne Moléculaire, 28 rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Laurence A. Mulard
- Institut
Pasteur, Université Paris Cité, CNRS UMR3523, Unité de Chimie des Biomolécules, 28 rue du Dr Roux, 75724 Paris Cedex 15, France
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3
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Toward a Multivalent Synthetic Oligosaccharide-Based Conjugate Vaccine against Shigella: State-of-the-Art for a Monovalent Prototype and Challenges. Vaccines (Basel) 2022; 10:vaccines10030403. [PMID: 35335035 PMCID: PMC8954881 DOI: 10.3390/vaccines10030403] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Revised: 02/15/2022] [Accepted: 02/19/2022] [Indexed: 02/04/2023] Open
Abstract
This review focuses on the molecular glycovaccine concept, a promising option to develop a Shigella glycoconjugate vaccine. Subsequent to original developments involving, as main vaccine component, the detoxified Shigella lipopolysaccharide randomly conjugated at multiple sites to a carrier protein, novelty stems from the use of rationally designed, well-defined chemically synthesized oligosaccharide haptens conceived as functional surrogates of the main surface antigen, linked via single-point attachment onto a carrier. The concept and design of such a fine-tuned Shigella glycovaccine are presented by way of SF2a-TT15, a neoglycoprotein featuring a synthetic 15-mer oligosaccharide, which constitutes an original vaccine prototype targeting Shigella flexneri 2a, one of the predominant circulating strains in endemic settings. The clinical testing of SF2a-TT15 is summarized with the first-in-human phase I trial in young healthy adults showing a good safety profile and tolerability, while inducing bactericidal antibodies towards S. flexneri 2a bacteria. The proof-of-concept of this novel approach being established, an ongoing phase IIa clinical study in the nine-month-old infant target population in endemic area was launched, which is also outlined. Lastly, some challenges to move forward this original approach toward a multivalent cost-effective Shigella synthetic glycan conjugate vaccine are introduced.
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4
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Wang L, Lowary TL. Synthesis of structurally-defined polymeric glycosylated phosphoprenols as potential lipopolysaccharide biosynthetic probes. Chem Sci 2021; 12:12192-12200. [PMID: 34667585 PMCID: PMC8457389 DOI: 10.1039/d1sc03852d] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 08/13/2021] [Indexed: 11/24/2022] Open
Abstract
The biosynthesis of lipopolysaccharide (LPS), a key immunomodulatory molecule produced by gram-negative bacteria, has been a topic of long-term interest. To date, the chemical probes used as tools to study LPS biosynthetic pathways have consisted primarily of small fragments of the larger structure (e.g., the O-chain repeating unit). While such compounds have helped to provide significant insight into many aspects of LPS assembly, understanding other aspects will require larger, more complex probes. For example, the molecular interactions between polymeric LPS biosynthetic intermediates and the proteins that transfer them across the inner and outer membrane remain largely unknown. We describe the synthesis of two lipid-linked polysaccharides, containing 11 and 27 monosaccharide residues, that are related to LPS O-chain biosynthesis in Escherichia coli O9a. This work has led not only to multi-milligram quantities of two biosynthetic probes, but also provided insights into challenges that must be overcome in the chemical synthesis of structurally-defined polysaccharides. The synthesis of lipid-linked polysaccharides containing 11 and 27 monosaccharides via a ‘frame-shift’ strategy is described. The work provides biosynthetic probes and highlights challenges in synthesizing structurally-defined polymeric glycans.![]()
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Affiliation(s)
- Lei Wang
- Department of Chemistry, University of Alberta Edmonton AB T6G 2G2 Canada
| | - Todd L Lowary
- Department of Chemistry, University of Alberta Edmonton AB T6G 2G2 Canada .,Institute of Biological Chemistry, Academia Sinica Academia Road, Section 2, #128, Nangang Taipei 11529 Taiwan.,Institute of Biochemical Sciences, National Taiwan University Section 4, #1, Roosevelt Road. Taipei 10617 Taiwan
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5
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Adegbite A, McCarthy PC. Recent and Future Advances in the Chemoenzymatic Synthesis of Homogeneous Glycans for Bacterial Glycoconjugate Vaccine Development. Vaccines (Basel) 2021; 9:1021. [PMID: 34579258 PMCID: PMC8473158 DOI: 10.3390/vaccines9091021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 09/09/2021] [Accepted: 09/10/2021] [Indexed: 12/02/2022] Open
Abstract
Vaccines are important in preventing disease outbreaks and controlling the spread of disease in a population. A variety of vaccines exist, including subunit, recombinant, and conjugate vaccines. Glycoconjugate vaccines have been an important tool to fight against diseases caused by a number of bacteria. Glycoconjugate vaccines are often heterogeneous. Vaccines of the future are becoming more rationally designed to have a defined oligosaccharide chain length and position of conjugation. Homogenous vaccines could play an important role in assessing the relationship between vaccine structure and immune response. This review focuses on recent advances in the chemoenzymatic production of defined bacterial oligosaccharides for vaccine development with a focus on Neisseria meningitidis and selected WHO-prioritized antibacterial resistant-pathogens. We also provide some perspective on future advances in the chemoenzymatic synthesis of well-defined oligosaccharides.
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Affiliation(s)
- Ayobami Adegbite
- Bioenvironmental Sciences Program, Morgan State University, Baltimore, MD 21251, USA;
- Department of Chemistry, Morgan State University, Baltimore, MD 21251, USA
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6
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Hu Z, Benkoulouche M, Barel LA, Le Heiget G, Ben Imeddourene A, Le Guen Y, Monties N, Guerreiro C, Remaud-Siméon M, Moulis C, André I, Mulard LA. Convergent Chemoenzymatic Strategy to Deliver a Diversity of Shigella flexneri Serotype-Specific O-Antigen Segments from a Unique Lightly Protected Tetrasaccharide Core. J Org Chem 2021; 86:2058-2075. [PMID: 32700907 DOI: 10.1021/acs.joc.0c00777] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Progress in glycoscience is strongly dependent on the availability of broadly diverse tailor-made, well-defined, and often complex oligosaccharides. Herein, going beyond natural resources and aiming to circumvent chemical boundaries in glycochemistry, we tackle the development of an in vitro chemoenzymatic strategy holding great potential to answer the need for molecular diversity characterizing microbial cell-surface carbohydrates. The concept is exemplified in the context of Shigella flexneri, a major cause of diarrhoeal disease. Aiming at a broad serotype coverage S. flexneri glycoconjugate vaccine, a non-natural lightly protected tetrasaccharide was designed for compatibility with (i) serotype-specific glucosylations and O-acetylations defining S. flexneri O-antigens, (ii) recognition by suitable α-transglucosylases, and (iii) programmed oligomerization following enzymatic α-d-glucosylation. The tetrasaccharide core was chemically synthesized from two crystalline monosaccharide precursors. Six α-transglucosylases found in the glycoside hydrolase family 70 were shown to transfer glucosyl residues on the non-natural acceptor. The successful proof of concept is achieved for a pentasaccharide featuring the glucosylation pattern from the S. flexneri type IV O-antigen. It demonstrates the potential of appropriately planned chemoenzymatic pathways involving non-natural acceptors and low-cost donor/transglucosylase systems to achieve the demanding regioselective α-d-glucosylation of large substrates, paving the way to microbial oligosaccharides of vaccinal interest.
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Affiliation(s)
- Zhaoyu Hu
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 Rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Mounir Benkoulouche
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France. 135, Avenue de Rangueil, F-31077 Toulouse Cedex 04, France
| | - Louis-Antoine Barel
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 Rue du Dr Roux, 75724 Paris Cedex 15, France.,Université Paris Descartes, Sorbonne Paris Cité, 75006 Paris, France
| | - Guillaume Le Heiget
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 Rue du Dr Roux, 75724 Paris Cedex 15, France.,Université Paris 13, Sorbonne Paris Cité, 93430 Paris, France
| | - Akli Ben Imeddourene
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France. 135, Avenue de Rangueil, F-31077 Toulouse Cedex 04, France
| | - Yann Le Guen
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 Rue du Dr Roux, 75724 Paris Cedex 15, France.,Université Paris Descartes, Sorbonne Paris Cité, 75006 Paris, France
| | - Nelly Monties
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France. 135, Avenue de Rangueil, F-31077 Toulouse Cedex 04, France
| | - Catherine Guerreiro
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 Rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Magali Remaud-Siméon
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France. 135, Avenue de Rangueil, F-31077 Toulouse Cedex 04, France
| | - Claire Moulis
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France. 135, Avenue de Rangueil, F-31077 Toulouse Cedex 04, France
| | - Isabelle André
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France. 135, Avenue de Rangueil, F-31077 Toulouse Cedex 04, France
| | - Laurence A Mulard
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 Rue du Dr Roux, 75724 Paris Cedex 15, France
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7
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Dhara D, Mulard LA. Exploratory N-Protecting Group Manipulation for the Total Synthesis of Zwitterionic Shigella sonnei Oligosaccharides. Chemistry 2021; 27:5694-5711. [PMID: 33314456 PMCID: PMC8048667 DOI: 10.1002/chem.202003480] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2020] [Revised: 09/23/2020] [Indexed: 12/16/2022]
Abstract
Shigella sonnei surface polysaccharides are well-established protective antigens against this major cause of diarrhoeal disease. They also qualify as unique zwitterionic polysaccharides (ZPSs) featuring a disaccharide repeating unit made of two 1,2-trans linked rare aminodeoxy sugars, a 2-acetamido-2-deoxy-l-altruronic acid (l-AltpNAcA) and a 2-acetamido-4-amino-2,4,6-trideoxy-d-galactopyranose (AAT). Herein, the stereoselective synthesis of S. sonnei oligosaccharides comprising two, three and four repeating units is reported for the first time. Several sets of up to seven protecting groups were explored, shedding light on the singular conformational behavior of protected altrosamine and altruronic residues. A disaccharide building block equipped with three distinct N-protecting groups and featuring the uronate moiety already in place was designed to accomplish the iterative high yielding glycosylation at the axial 4-OH of the altruronate component and achieve the challenging full deprotection step. Key to the successful route was the use of a diacetyl strategy whereby the N-acetamido group of the l-AltpNAcA is masked in the form of an imide.
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Affiliation(s)
- Debashis Dhara
- Unité de Chimie des BiomoléculesUMR 3523 CNRS, Institut Pasteur28 rue du Dr Roux75015ParisFrance
| | - Laurence A. Mulard
- Unité de Chimie des BiomoléculesUMR 3523 CNRS, Institut Pasteur28 rue du Dr Roux75015ParisFrance
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8
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Cornil J, Hu Z, Bouchet M, Mulard LA. Multigram synthesis of an orthogonally-protected pentasaccharide for use as a glycan precursor in a Shigella flexneri 3a conjugate vaccine: application to a ready-for-conjugation decasaccharide. Org Chem Front 2021. [DOI: 10.1039/d1qo00761k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Fine-tuned catalytic processes facilitating regio- and stereoselective conversions for the large-scale synthesis of a pentasaccharide and its oligomerization into ready-for-conjugation haptens.
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Affiliation(s)
- Johan Cornil
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 rue du Dr Roux, 75 724 Paris Cedex 15, France
| | - Zhaoyu Hu
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 rue du Dr Roux, 75 724 Paris Cedex 15, France
| | - Marion Bouchet
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 rue du Dr Roux, 75 724 Paris Cedex 15, France
| | - Laurence A. Mulard
- Unité de Chimie des Biomolécules, Institut Pasteur, UMR3523 CNRS, 28 rue du Dr Roux, 75 724 Paris Cedex 15, France
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9
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Barel LA, Mulard LA. Classical and novel strategies to develop a Shigella glycoconjugate vaccine: from concept to efficacy in human. Hum Vaccin Immunother 2020; 15:1338-1356. [PMID: 31158047 PMCID: PMC6663142 DOI: 10.1080/21645515.2019.1606972] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Shigella are gram-negative bacteria that cause severe diarrhea and dysentery, with a high level of antimicrobial resistance. Disease-induced protection against reinfection in Shigella-endemic areas provides convincing evidence on the feasibility of a vaccine and on the importance of Shigella lipopolysaccharides as targets of the host humoral protective immune response against disease. This article provides an overview of the original and current strategies toward the development of a Shigella glycan-protein conjugate vaccine that would cover the most commonly detected strains. Going beyond pioneering “lattice”-type polysaccharide-protein conjugates, progress, and challenges are addressed with focus on promising alternatives, which have reached phases I and II clinical trial. Glycoengineered bioconjugates and “sun”-type conjugates featuring well-defined synthetic carbohydrate antigens are discussed with insights on the molecular parameters governing the rational design of a cost-effective glycoconjugate vaccine efficacious in preventing diseases caused by Shigella in the most at risk populations, young children living in endemic areas.
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Affiliation(s)
- Louis-Antoine Barel
- a Chemistry of Biomolecules Unit, Department of Structural Biology and Chemistry , Institut Pasteur, UMR3523, CNRS , Paris , France.,b Université Paris Descartes , Paris , France
| | - Laurence A Mulard
- a Chemistry of Biomolecules Unit, Department of Structural Biology and Chemistry , Institut Pasteur, UMR3523, CNRS , Paris , France
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10
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Selectively Charged and Zwitterionic Analogues of the Smallest Immunogenic Structure of Streptococcus Pneumoniae Type 14. Molecules 2019; 24:molecules24183414. [PMID: 31546911 PMCID: PMC6767069 DOI: 10.3390/molecules24183414] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Revised: 09/16/2019] [Accepted: 09/17/2019] [Indexed: 11/19/2022] Open
Abstract
Zwitterionic polysaccharides (ZPs) have been shown in recent years to display peculiar immunological properties, thus attracting the interest of the carbohydrate research community. To fully elucidate the mechanisms underlying these properties and exploit the potential of this kind of structures, in depth studies are still required. In this context, the preparation of two cationic, an anionic, as well as two zwitterionic tetrasaccharide analogues of the smallest immunogenic structure of Streptococcus pneumoniae type 14 (SP14) capsular polysaccharide are presented. By exploiting a block strategy, the negative charge has been installed on the non-reducing end of the lactose unit of the tetrasaccharide and the positive charge either on the non-reducing end of the lactosamine moiety or on an external linker. These structures have then been tested by competitive ELISA, showing that the structural variations we made do not modify the affinity of the neutral compound to binding to a specific antibody. However, lower efficacies than the natural SP14 compound were observed. The results obtained, although promising, point to the need to further elongate the polysaccharide structure, which is likely too short to cover the entire epitopes.
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11
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Berti F, Adamo R. Antimicrobial glycoconjugate vaccines: an overview of classic and modern approaches for protein modification. Chem Soc Rev 2018; 47:9015-9025. [PMID: 30277489 DOI: 10.1039/c8cs00495a] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Glycoconjugate vaccines obtained by chemical linkage of a carbohydrate antigen to a protein are part of routine vaccinations in many countries. Licensed antimicrobial glycan-protein conjugate vaccines are obtained by random conjugation of native or sized polysaccharides to lysine, aspartic or glutamic amino acid residues that are generally abundantly exposed on the protein surface. In the last few years, the structural approaches for the definition of the polysaccharide portion (epitope) responsible for the immunological activity has shown potential to aid a deeper understanding of the mode of action of glycoconjugates and to lead to the rational design of more efficacious and safer vaccines. The combination of technologies to obtain more defined carbohydrate antigens of higher purity and novel approaches for protein modification has a fundamental role. In particular, methods for site selective glycoconjugation like chemical or enzymatic modification of specific amino acid residues, incorporation of unnatural amino acids and glycoengineering, are rapidly evolving. Here we discuss the state of the art of protein engineering with carbohydrates to obtain glycococonjugates vaccines and future perspectives.
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