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Iyer AS, Azman AS, Bouhenia M, Deng LO, Anderson CP, Graves M, Kováč P, Xu P, Ryan ET, Harris JB, Sack DA, Luquero FJ, Leung DT. Dried Blood Spots for Measuring Vibrio cholerae-specific Immune Responses. PLoS Negl Trop Dis 2018; 12:e0006196. [PMID: 29377882 PMCID: PMC5805362 DOI: 10.1371/journal.pntd.0006196] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Revised: 02/08/2018] [Accepted: 12/28/2017] [Indexed: 02/03/2023] Open
Abstract
Background Vibrio cholerae causes over 2 million cases of cholera and 90,000 deaths each year. Serosurveillance can be a useful tool for estimating the intensity of cholera transmission and prioritizing populations for cholera control interventions. Current methods involving venous blood draws and downstream specimen storage and transport methods pose logistical challenges in most settings where cholera strikes. To overcome these challenges, we developed methods for determining cholera-specific immune responses from dried blood spots (DBS). Methodology/principal findings As conventional vibriocidal assay methods were unsuitable for DBS eluates from filter paper, we adopted a drop-plate culture method. We show that DBS collected from volunteers in South Sudan, and stored for prolonged periods in field conditions, retained functional vibriocidal antibodies, the titers of which correlated with paired serum titers determined by conventional spectrophotometric methods (r = 0.94, p = 0.00012). We also showed that eluates from DBS Serum Separator cards could be used with conventional spectrophotometric vibriocidal methods, and that they correlated with paired serum at a wide range of titers (r = 0.96, p<0.0001). Similarly, we used ELISA methods to show that V. cholerae O-specific polysaccharide antibody responses from DBS eluates correlated with results from paired serum for IgG (r = 0.85, p = 0.00006), IgM (r = 0.79, p = 0.00049) and IgA (r = 0.73, p = 0.0019), highlighting its potential for use in determination of isotype-specific responses. Storage of DBS cards at a range of temperatures did not change antibody responses. Conclusion In conclusion, we have developed and demonstrated a proof-of-concept for assays utilizing DBS for assessing cholera-specific immune responses. Cholera remains a major public health issue among underprivileged populations in the developing world. Current methods of disease surveillance are inadequate for identifying key populations at highest risk of cholera. Serosurveillance can provide accurate measurements of an individual or population’s exposure to cholera infection or oral cholera vaccine (OCV) induced immunity, though they require venous blood draw and stringent processing needs. Dried blood spots (DBS) overcome these challenges, acting as a portable surveillance tool suitable for field use. We developed a drop-plate culture method for evaluating vibriocidal and cholera-specific isotype responses using DBS from OCV-immunized volunteers from South Sudan. Blood equivalent to only two drops were spotted on Whatman Protein Saver (WPS) DBS cards. Vibriocidal titers from WPS eluates determined by drop-plate culture methods correlated well with serum based assays. In addition, by using DBS cards capable of automatic separation of serum from blood, we demonstrate that vibriocidal titers and V. cholerae polysaccharide antibody responses could be measured by conventional spectrophotometric methods and that these responses are stable over a range of storage temperatures. In summary, we show that cholera-specific immune responses can be measured using DBS, providing a potential tool for large-scale serosurveillance field studies for cholera.
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Xu P, Kelly M, Vann WF, Qadri F, Ryan ET, Kováč P. Conjugate Vaccines from Bacterial Antigens by Squaric Acid Chemistry: A Closer Look. Chembiochem 2017; 18:799-815. [PMID: 28182850 PMCID: PMC5664186 DOI: 10.1002/cbic.201600699] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Indexed: 11/09/2022]
Abstract
By using O-SP-core (O-SPcNH2 ) polysaccharide, isolated from Vibrio cholera O1 lipopolysaccharide (LPS) and related synthetic substances, a detailed study of factors that affect conjugation of bacterial polysaccharides to protein carriers through squaric acid chemistry to form conjugate vaccines has been carried out. Several previously unrecognized processes that take place during the squarate labeling of the O-SPcNH2 and subsequent conjugation of the formed squarate (O-SPcNH-SqOMe) have been identified. The efficiency of conjugation at pH 8.5, 9.0, and 9.5 to bovine serum albumin (BSA) and to the recombinant tetanus toxin fragment C (rTT-Hc) has been determined. The study led to a protocol for more efficient labeling of O-SPcNH2 antigen with the methyl squarate group, to yield a higher-quality, more potent squarate conjugation reagent. Its use resulted in about twofold increases in conjugation efficiency (from 23-26 % on BSA to 51 % on BSA and 55 % on rTT-Hc). The spent conjugation reagent could be recovered and regenerated by treatment with MeI in the absence of additional base. The immunological properties of the experimental vaccine made from the regenerated conjugation reagent were comparable with those of the immunogen made from the parent O-SPcNH-SqOMe.
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Kushwaha D, Xu P, Kováč P. Carbohydrates as potentially versatile core subcarriers for multivalent immunogens. RSC Adv 2017; 7:7591-7603. [PMID: 28944050 PMCID: PMC5607872 DOI: 10.1039/c6ra27181b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synthetic multivalent glycoclusters that carry carbohydrate antigen epitopes have been recognized as promising candidates for the development of carbohydrate based vaccines. Here we describe a convergent strategy for the synthesis of conjugation-ready multivalent glycoclusters using sugars as versatile core subcarriers. d-Glucose and gentiobiose were converted into poly-alkyne functionalized cores which were then decorated with an azide bearing model ligand d-glucose using click chemistry, to form structurally well-defined tetra- and heptavalent glycoclusters. Each cluster was conjugated to a model protein bovine serum albumin (BSA) by squaric acid chemistry. Carbohydrate clusters can be prepared in a variety of sizes and spatial arrangements by altering the structure and configuration of the core, depending on the mono-, or oligosaccharides used for their assembly. It is suggested that the use of carbohydrate as core subcarriers provides an opportunity to tailor the size and topology of antigens and modify multivalent presentation of immunogens in a way to optimize cluster effect for stronger immunoreactivity.
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Soliman SE, Kováč P. Total Synthesis of the Complete Protective Antigen ofVibrio choleraeO139. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201606116] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Soliman SE, Kováč P. Total Synthesis of the Complete Protective Antigen of Vibrio cholerae O139. Angew Chem Int Ed Engl 2016; 55:12850-3. [PMID: 27623688 DOI: 10.1002/anie.201606116] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Indexed: 01/09/2023]
Abstract
The first chemical synthesis of the complete protective O-antigen of a human-disease-causing pathogenic bacterium is described. The synthesis involved a protecting-group strategy that facilitated the regioselectivity of the key transformations, stereoselective glycosylation reactions, and enabled the one-step global deprotection of the completely assembled, fully protected, phosphorylated hexasaccharide by hydrogenation/hydrogenolysis. The final amino-group-functionalized, linker-equipped antigen was obtained in a form ready for conjugation to suitable carriers, for example, proteins, to yield immunogens.
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Kováč P. Synthesis Of Ligands Related To The O-Specific Antigen OfShigella DysenteriaeType 1. J Carbohydr Chem 2016. [DOI: 10.1080/07328303.1992.11760693] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Lu X, Kováč P. Chemical Synthesis of the Galacturonic Acid Containing Pentasaccharide Antigen of the O-Specific Polysaccharide of Vibrio cholerae O139 and Its Five Fragments. J Org Chem 2016; 81:6374-94. [DOI: 10.1021/acs.joc.6b01019] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Matias WR, Falkard B, Charles RC, Mayo-Smith LM, Teng JE, Xu P, Kováč P, Ryan ET, Qadri F, Franke MF, Ivers LC, Harris JB. Antibody Secreting Cell Responses following Vaccination with Bivalent Oral Cholera Vaccine among Haitian Adults. PLoS Negl Trop Dis 2016; 10:e0004753. [PMID: 27308825 PMCID: PMC4911095 DOI: 10.1371/journal.pntd.0004753] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Accepted: 05/11/2016] [Indexed: 11/19/2022] Open
Abstract
Background The bivalent whole-cell (BivWC) oral cholera vaccine (Shanchol) is effective in preventing cholera. However, evaluations of immune responses following vaccination with BivWC have been limited. To determine whether BivWC induces significant mucosal immune responses, we measured V. cholerae O1 antigen-specific antibody secreting cell (ASC) responses following vaccination. Methodology/Principal Findings We enrolled 24 Haitian adults in this study, and administered doses of oral BivWC vaccine 14 days apart (day 0 and day 14). We drew blood at baseline, and 7 days following each vaccine dose (day 7 and 21). Peripheral blood mononuclear cells (PBMCs) were isolated, and ASCs were enumerated using an ELISPOT assay. Significant increases in Ogawa (6.9 cells per million PBMCs) and Inaba (9.5 cells per million PBMCs) OSP-specific IgA ASCs were detected 7 days following the first dose (P < 0.001), but not the second dose. The magnitude of V. cholerae-specific ASC responses did not appear to be associated with recent exposure to cholera. ASC responses measured against the whole lipolysaccharide (LPS) antigen and the OSP moiety of LPS were equivalent, suggesting that all or nearly all of the LPS response targets the OSP moiety. Conclusions/Significance Immunization with the BivWC oral cholera vaccine induced ASC responses among a cohort of healthy adults in Haiti after a single dose. The second dose of vaccine resulted in minimal ASC responses over baseline, suggesting that the current dosing schedule may not be optimal for boosting mucosal immune responses to V. cholerae antigens for adults in a cholera-endemic area. The bivalent whole-cell (BivWC) oral cholera vaccine (Shanchol) is effective in preventing cholera. Despite its increasing use as part of comprehensive cholera prevention and control efforts, evaluations of immune responses following vaccination with BivWC have been limited. In this study, we measured the development of cholera-specific antibody secreting cells, markers of mucosal immunity, following vaccination with BivWC among a population of adults in Haiti, where cholera is now endemic. BivWC induced development of robust immune responses following the first dose of vaccine, but similar ASC responses were not detected following the second dose, suggesting that the currently recommended 14-day interval between doses may not be optimal for boosting mucosal immune responses among adults in cholera endemic regions. These findings suggest that additional evaluation of the optimal dosing schedule for oral cholera vaccines is warranted with the goal of improving long-term immunity.
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Soliman SE, Kováč P. Synthesis of a Conjugation-Ready, Phosphorylated, Tetrasaccharide Fragment of the O-PS of Vibrio cholerae O139. J Org Chem 2015; 80:11227-32. [DOI: 10.1021/acs.joc.5b02105] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Soliman SE, Kováč P. Stereoselective Syntheses of the Conjugation-Ready, Downstream Disaccharide and Phosphorylated Upstream, Branched Trisaccharide Fragments of the O-PS of Vibrio cholerae O139. J Org Chem 2015; 80:4851-60. [DOI: 10.1021/acs.joc.5b00562] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Xu P, Stevens ED, French AD, Kováč P. Synthesis and molecular structure of the 5-methoxycarbonylpentyl α-glycoside of the upstream, terminal moiety of the O-specific polysaccharide of Vibrio cholerae O1, serotype Inaba. Molecules 2015; 20:2892-902. [PMID: 25679049 PMCID: PMC6272311 DOI: 10.3390/molecules20022892] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 02/05/2015] [Indexed: 11/16/2022] Open
Abstract
The trimethylsilyl trifluoromethanesulfonate (TMSOTf)-catalyzed reaction of methyl 6-hydroxyhexanoate with 3-O-benzyl-4-(2,4-di-O-acetyl-3-deoxy-l-glycero-tetronamido)-4,6-dideoxy-2-O-levulinoyl-α-d-mannopyranosyl trichloroacetimidate followed by a two-step deprotection (hydrogenolysis over Pd/C catalyst and Zemplén deacylation, to simultaneously remove the acetyl and levulinoyl groups) gave 5-(methoxycarbonyl)pentyl 4-(3-deoxy-l-glycero-tetronamido)-4,6-dideoxy-α-d-mannopyranoside. The structure of the latter, for which crystals were obtained in the analytically pure state for the first time, followed from its NMR and high-resolution mass spectra and was confirmed by X-ray crystallography. The molecule has two approximately linear components; a line through the aglycon intersects a line through the mannosyl and tetronylamido groups at 120°. The crystal packing separates the aglycon groups from the tetronylamido and mannosyl groups, with only C-H…O hydrogen bonding among the aglycon groups and N-H…O, O-H…O and C-H…O links among the tetronylamido and mannosyl groups. A carbonyl oxygen atom accepts the strongest O-H…O hydrogen bond and two strong C-H…O hydrogen bonds. The geometric properties were compared with those of related molecules.
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Uddin T, Aktar A, Xu P, Johnson RA, Rahman MA, Leung DT, Afrin S, Akter A, Alam MM, Rahman A, Chowdhury F, Khan AI, Bhuiyan TR, Bufano MK, Rashu R, Yu Y, Wu-Freeman Y, Harris JB, LaRocque RC, Charles RC, Kováč P, Calderwood SB, Ryan ET, Qadri F. Immune responses to O-specific polysaccharide and lipopolysaccharide of Vibrio cholerae O1 Ogawa in adult Bangladeshi recipients of an oral killed cholera vaccine and comparison to responses in patients with cholera. Am J Trop Med Hyg 2014; 90:873-81. [PMID: 24686738 DOI: 10.4269/ajtmh.13-0498] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Protective immunity to cholera is serogroup specific, and serogrouping is defined by the O-specific polysaccharide (OSP) of lipopolysaccharide (LPS). We characterized OSP-specific immune responses in adult recipients of an oral killed cholera vaccine (OCV WC-rBS) and compared these with responses in patients with cholera caused by Vibrio cholerae O1 Ogawa. Although vaccinees developed plasma immunoglobulin G (IgG), IgM, IgA antibody and antibody secreting cell (ASC, marker of mucosal response) to Ogawa OSP and LPS 7 days after vaccination, responses were significantly lower than that which occurred after cholera. Similarly, patients recovering from cholera had detectable IgA, IgM, and IgG memory B cell (MBC) responses against OSP and LPS on Day 30 and Day 90, whereas vaccinees only developed IgG responses to OSP 30 days after the second immunization. The markedly lower ASC and MBC responses to OSP and LPS observed among vaccinees might explain, in part, the lower protection of an OCV compared with natural infection.
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Kováč P, Xu P, Dauter Z. Synthesis, Characterization, and Crystal Structure of Sodium (Methyl α-d-Mannopyranosid)uronate Monohydrate. SYNTHESIS-STUTTGART 2014. [DOI: 10.1055/s-0033-1340843] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Alam MM, Bufano MK, Xu P, Kalsy A, Yu Y, Freeman YW, Sultana T, Rashu MR, Desai I, Eckhoff G, Leung DT, Charles RC, LaRocque RC, Harris JB, Clements JD, Calderwood SB, Qadri F, Vann WF, Kováč P, Ryan ET. Evaluation in mice of a conjugate vaccine for cholera made from Vibrio cholerae O1 (Ogawa) O-specific polysaccharide. PLoS Negl Trop Dis 2014; 8:e2683. [PMID: 24516685 PMCID: PMC3916310 DOI: 10.1371/journal.pntd.0002683] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Accepted: 12/18/2013] [Indexed: 11/18/2022] Open
Abstract
Background Protective immunity against cholera is serogroup specific. Serogroup specificity in Vibrio cholerae is determined by the O-specific polysaccharide (OSP) of lipopolysaccharide (LPS). Generally, polysaccharides are poorly immunogenic, especially in young children. Methodology Here we report the evaluation in mice of a conjugate vaccine for cholera (OSP:TThc) made from V. cholerae O1 Ogawa O-Specific Polysaccharide–core (OSP) and recombinant tetanus toxoid heavy chain fragment (TThc). We immunized mice intramuscularly on days 0, 21, and 42 with OSP:TThc or OSP only, with or without dmLT, a non-toxigenic immunoadjuvant derived from heat labile toxin of Escherichia coli. Principal Findings We detected significant serum IgG antibody responses targeting OSP following a single immunization in mice receiving OSP:TThc with or without adjuvant. Anti-LPS IgG responses were detected following a second immunization in these cohorts. No anti-OSP or anti-LPS IgG responses were detected at any time in animals receiving un-conjugated OSP with or without immunoadjuvant, and in animals receiving immunoadjuvant alone. Responses were highest following immunization with adjuvant. Serum anti-OSP IgM responses were detected in mice receiving OSP:TThc with or without immunoadjuvant, and in mice receiving unconjugated OSP. Serum anti-LPS IgM and vibriocidal responses were detected in all vaccine cohorts except in mice receiving immunoadjuvant alone. No significant IgA anti-OSP or anti-LPS responses developed in any group. Administration of OSP:TThc and adjuvant also induced memory B cell responses targeting OSP and resulted in 95% protective efficacy in a mouse lethality cholera challenge model. Conclusion We describe a protectively immunogenic cholera conjugate in mice. Development of a cholera conjugate vaccine could assist in inducing long-term protective immunity, especially in young children who respond poorly to polysaccharide antigens. Cholera is a severe dehydrating diarrheal illness of humans caused by organisms Vibrio cholerae serogroups O1 or O139 serogroup organisms. Protective immunity against cholera is serogroup specific. Serogroup specificity in V. cholerae is determined by the O-specific polysaccharide (OSP) of lipopolysaccharide (LPS). Generally, polysaccharides are poorly immunogenic, especially in young children. Unfortunately, children bear a large burden of cholera globally. Here we describe a novel cholera conjugate vaccine and show that it induces immune responses in mice, including memory responses, to OSP, the T cell-independent antigen that probably is the target of protective immunity to cholera. These responses were highest following immunization of the vaccine with a novel immunoadjuvant, dmLT. We also show that immunization of mice with this conjugate vaccine protects against challenge with wild-type V. cholerae. A protectively immunogenic cholera conjugate vaccine that induces long-term memory responses could have particular utility in young children who are most at risk of cholera.
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Kováč P, Soliman S. Practical Synthesis of Building Blocks for Oligosaccharides Containing the β-d-Galp-(1→3)-β-d-GlcpNAc Motif. SYNTHESIS-STUTTGART 2014. [DOI: 10.1055/s-0033-1340620] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Jahouh F, Xu P, Vann WF, Kováč P, Banoub JH. Mapping the glycation sites in the neoglycoconjugate from hexasaccharide antigen of Vibrio cholerae, serotype Ogawa and the recombinant tetanus toxin C-fragment carrier. JOURNAL OF MASS SPECTROMETRY : JMS 2013; 48:1083-1090. [PMID: 24130011 PMCID: PMC4155328 DOI: 10.1002/jms.3258] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 07/24/2013] [Accepted: 07/25/2013] [Indexed: 06/02/2023]
Abstract
We report herein the glycation sites in a vaccine candidate for cholera formed by conjugation of the synthetic hexasaccharide fragment of the O-specific polysaccharide of Vibrio cholerae, serotype Ogawa, to the recombinant tetanus toxin C-fragment (rTT-Hc) carrier. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of the vaccine revealed that it is composed of a mixture of neoglycoconjugates with carbohydrate : protein ratios of 1.9 : 1, 3.0 : 1, 4.0 : 1, 4.9 : 1, 5.9 : 1, 6.9 : 1, 7.9 : 1 and 9.1 : 1. Liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis of the tryptic and GluC V8 digests allowed identification of 12 glycation sites in the carbohydrate-protein neoglycoconjugate vaccine. The glycation sites are located exclusively on lysine (Lys) residues and are listed as follows: Lys 22, Lys 61, Lys 145, Lys 239, Lys 278, Lys 318, Lys 331, Lys 353, Lys 378, Lys 389, Lys 396 and Lys 437. Based on the 3-D representation of the rTT-Hc protein, all the glycation sites correspond to lysines located at the outer surface of the protein.
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Kováč P, Lu X, Sail D. 4′,6′-O-Benzylidene- and 4′,6′-O-p-Methoxybenzylidene-α,β-cellobiose and Their Hexa-O-β-benzoyl Derivatives. SYNTHESIS-STUTTGART 2013. [DOI: 10.1055/s-0033-1339174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Sail D, Kováč P. Benzoylated ethyl 1-thioglycosides: direct preparation from per-O-benzoylated sugars. Carbohydr Res 2012; 357:47-52. [PMID: 22739243 PMCID: PMC3568975 DOI: 10.1016/j.carres.2012.05.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 05/14/2012] [Accepted: 05/15/2012] [Indexed: 10/28/2022]
Abstract
D-Glucose, lactose, maltose, and melibiose were benzoylated with Bz(2)O-Et(3)N reagent to give fully benzoylated β products. Under the same conditions, D-mannose produced a mixture where the β-benzoate predominated. Treatment of the foregoing compounds with EtSH at slightly elevated temperature (50-60°C) in the presence of BF(3)·Et(2)O as a promoter gave the corresponding ethyl 1-thio glycosides in high yields. The α-products predominated in all cases in the anomeric mixtures formed. Individual products of all reactions were isolated by chromatography, they were obtained in analytically pure state, and were fully characterized by (1)H and (13)C NMR data and physical constants.
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Jahouh F, Saksena R, Kováč P, Banoub J. Revealing the glycation sites in synthetic neoglycoconjugates formed by conjugation of the antigenic monosaccharide hapten of Vibrio cholerae O1, serotype Ogawa with the BSA protein carrier using LC-ESI-QqTOF-MS/MS. JOURNAL OF MASS SPECTROMETRY : JMS 2012; 47:890-900. [PMID: 22791257 PMCID: PMC3427934 DOI: 10.1002/jms.2974] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In this manuscript, we present the determination of glycation sites in synthetic neoglycoconjugates formed by conjugation of the antigenic monosaccharide hapten of Vibrio cholerae O1 serotype Ogawa to BSA using nano- liquid chromatography electrospray ionization quadrupole time-of-flight tandem mass spectroscopy (LC-ESI-QqTOF-MS/MS). The matrix-assisted laser desorption/ionization-TOF/TOF-MS/MS analyses of the tryptic digests of the glycoconjugates having a hapten:BSA ratio of 4.3:1, 6.6:1 and 13.2:1 revealed only three glycation sites, on the following lysine residues: Lys 235, Lys 437 and Lys 455. Digestion of the neoglycoconjugates with the proteases trypsin and GluC V8 gave complementary structural information and was shown to maximize the number of recognized glycation sites. Here, we report identification of 20, 27 and 33 glycation sites using LC-ESI-QqTOF-MS/MS analysis of a series of synthetic neoglycoconjugates with a hapten:BSA ratio of, respectively, 4.3:1, 6.6:1 and 13.2:1. We also tentatively propose that all the glycated lysine residues are located mainly near the outer surface of the protein.
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Ling NXY, Lee J, Ellis M, Liao ML, Mau SL, Guest D, Janssen PH, Kováč P, Bacic A, Pettolino FA. An exo-β-(1→3)-D-galactanase from Streptomyces sp. provides insights into type II arabinogalactan structure. Carbohydr Res 2012; 352:70-81. [PMID: 22464224 PMCID: PMC3419940 DOI: 10.1016/j.carres.2012.02.033] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 02/21/2012] [Accepted: 02/28/2012] [Indexed: 11/29/2022]
Abstract
An exo-β-(1→3)-D-galactanase (SGalase1) that specifically cleaves the β-(1→3)-D-galactan backbone of arabinogalactan-proteins (AGPs) was isolated from culture filtrates of a soil Streptomyces sp. Internal peptide sequence information was used to clone and recombinantly express the gene in E. coli. The molecular mass of the isolated enzyme was ~45 kDa, similar to the 48.2 kDa mass predicted from the amino acid sequence. The pI, pH and temperature optima for the enzyme were ~7.45, 3.8 and 48 °C, respectively. The native and recombinant enzymes specifically hydrolysed β-(1→3)-D-galacto-oligo- or poly-saccharides from the upstream (non-reducing) end, typical of an exo-acting enzyme. A second homologous Streptomyces gene (SGalase2) was also cloned and expressed. SGalase2 was similar in size (47.9 kDa) and enzyme activity to SGalase1 but differed in its pH optimum (pH 5). Both SGalase1 and SGalase2 are predicted to belong to the CAZy glycosyl hydrolase family GH 43 based on activity, sequence homology and phylogenetic analysis. The K(m) and V(max) of the native exo-β-(1→3)-D-galactanase for de-arabinosylated gum arabic (dGA) were 19 mg/ml and 9.7 μmol D-Gal/min/mg protein, respectively. The activity of these enzymes is well suited for the study of type II galactan structures and provides an important tool for the investigation of the biological role of AGPs in plants. De-arabinosylated gum arabic (dGA) was used as a model to investigate the use of these enzymes in defining type II galactan structure. Exhaustive hydrolysis of dGA resulted in a limited number of oligosaccharide products with a trisaccharide of Gal(2)GlcA(1) predominating.
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Jahouh F, Hou SJ, Kováč P, Banoub JH. Determination of glycation sites by tandem mass spectrometry in a synthetic lactose-bovine serum albumin conjugate, a vaccine model prepared by dialkyl squarate chemistry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2012; 26:749-58. [PMID: 22368054 PMCID: PMC3417241 DOI: 10.1002/rcm.6166] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
RATIONALE Neoglycoconjugate vaccines synthesized by the squaric acid spacer method allow single point attachment of the carbohydrate antigen to the protein carrier. However, the localization of the carbohydrate antigen sites of conjugation on the protein carrier has been an elusive task difficult to achieve. METHOD Covalent attachment of the lactose antigen to the bovine serum albumin (BSA) was prepared by the squaric acid method using a hapten:BSA ratio of 20:1. Different reaction times were used during the conjugation reaction and two different lactose-BSA glycoconjugate vaccines were obtained. The carbohydrate antigen hapten:BSA ratios of these lactose-BSA glycoconjugate vaccines were determined by MALDI-TOF/RTOF-MS and the glycation sites in the neoglycoconjugates were determined using nano-LC/ESI-QqTOF-MS/MS analysis of the trypsin and GluC V8 digests of the conjugates. RESULTS We have identified a total of 15 glycation sites located on the BSA lysine residues for the neoglycoconjugate vaccine formed with a hapten:BSA ratio of 5.1:1, However, the tryptic and GluC V8 digests of the hapten-BSA glycoconjugate with a hapten:BSA ratio of 19.0:1 allowed identification of 30 glycation sites located on the BSA. These last results seem to indicate that this conjugation results in formation of various glycoforms. CONCLUSIONS It was observed that the number of identified glycation sites increased when the hapten:BSA ratio of glycoconjugate formation increased, and that the location of the glycation sites appears to be mainly on the outer surface of the BSA carrier molecule which is in line with the assumption that the sterically more accessible lysine residues, namely those located on the outer surface of the BSA, would be conjugated preferentially.
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MESH Headings
- Amino Acid Sequence
- Animals
- Cattle
- Chromatography, Liquid
- Glycosylation
- Haptens/chemistry
- Haptens/metabolism
- Lactose/chemistry
- Lactose/immunology
- Lactose/metabolism
- Lysine/chemistry
- Lysine/metabolism
- Models, Molecular
- Molecular Sequence Data
- Peptide Fragments/chemistry
- Peptide Fragments/metabolism
- Serum Albumin, Bovine/chemistry
- Serum Albumin, Bovine/immunology
- Serum Albumin, Bovine/metabolism
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
- Tandem Mass Spectrometry/methods
- Vaccines, Conjugate/chemistry
- Vaccines, Conjugate/immunology
- Vaccines, Conjugate/metabolism
- Vaccines, Subunit/chemistry
- Vaccines, Subunit/immunology
- Vaccines, Subunit/metabolism
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Kováč P, Hou SJ, Sail D. Towards the First Chemical Synthesis of the Hexasaccharide O-Antigen of Vibrio cholerae O139. Synlett 2011. [DOI: 10.1055/s-0031-1289876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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49
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Xu P, Alam MM, Kalsy A, Charles RC, Calderwood SB, Qadri F, Ryan ET, Kováč P. Simple, direct conjugation of bacterial O-SP-core antigens to proteins: development of cholera conjugate vaccines. Bioconjug Chem 2011; 22:2179-85. [PMID: 21899371 PMCID: PMC3197769 DOI: 10.1021/bc2001984] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bacterial O-SP-core antigens can be conjugated to proteins in the same, simple way as synthetic, linker-equipped carbohydrates by applying squaric acid chemistry. Introduction of spacers (linkers) to either O-SP-core antigens or protein carriers, which is involved in commonly applied protocols, is not required. The newly developed method described here consists of preparation of a squaric acid monoester derivative of O-SP-core antigen, utilizing the amino group inherent in the core, and reaction of the monoester with the carrier protein. The intermediate monoester can be easily purified; its conjugation can be monitored by SELDI-TOF mass spectrometry and, thus, readily controlled, since the conjugation can be terminated when the desired carbohydrate-protein ratio is reached. Here, we describe production of conjugates containing the O-SP-core antigen of Vibrio cholerae O1, the major cause of cholera, a severe dehydrating diarrheal disease of humans. The resultant products are recognized by convalescent phase sera from patients recovering from cholera in Bangladesh, and anti-O-SP-core-protein responses correlate with plasma antilipopolysaccharide and vibriocidal responses, which are the primary markers of protection from cholera. The results suggest that such conjugates have potential as vaccines for cholera and other bacterial diseases.
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Jahouh F, Hou SJ, Kováč P, Banoub JH. Determination of the glycation sites of Bacillus anthracis neoglycoconjugate vaccine by MALDI-TOF/TOF-CID-MS/MS and LC-ESI-QqTOF-tandem mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2011; 46:993-1003. [PMID: 22012665 PMCID: PMC3427925 DOI: 10.1002/jms.1980] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We present herein an efficient mass spectrometric method for the localization of the glycation sites of a model neoglycoconjugate vaccine formed by a construct of the tetrasaccharide side chain of the Bacillus anthracis exosporium and the protein carrier bovine serum albumin. The glycoconjugate was digested with both trypsin and GluC V8 endoproteinases, and the digests were then analyzed by MALDI-TOF/TOF-CID-MS/MS and nano-LC-ESI-QqTOF-CID-MS/MS. The sequences of the unknown peptides analyzed by MALDI-TOF/TOF-CID-MS/MS, following digestion with the GluC V8 endoproteinase, allowed us to recognize three glycopeptides whose glycation occupancies were, respectively, on Lys 235, Lys 420, and Lys 498. Similarly, the same analysis was performed on the tryptic digests, which permitted us to recognize two glycation sites on Lys 100 and Lys 374. In addition, we have also used LC-ESI-QqTOF-CID-MS/MS analysis for the identification of the tryptic digests. However, this analysis identified a higher number of glycopeptides than would be expected from a glycoconjugate composed of a carbohydrate-protein ratio of 5.4:1, which would have resulted in glycation occupancies of 18 specific sites. This discrepancy was due to the large number of glycoforms formed during the synthetic carbohydrate-spacer-carrier protein conjugation. Likewise, the LC-ESI-QqTOF-MS/MS analysis of the GluC V8 digest also identified 17 different glycation sites on the synthetic glycoconjugate.
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