Purification and characterization of a rhamnose-containing cell wall antigen of Streptococcus mutans B13 (serotype d)

The Zebrafish Perivitelline Fluid Provides Maternally-Inherited Defensive Immunity

In the teleost egg, the embryo is immersed in an extraembryonic fluid that fills the space between the embryo and the chorion and partially isolates it from the external environment, called the perivitelline fluid (PVF). The exact composition of the PVF remains unknown in vertebrate animals. The PVF allows the embryo to avoid dehydration, to maintain a safe osmotic balance and provides mechanical protection; however, its potential defensive properties against bacterial pathogens has not been reported. In this work, we determined the global proteomic profile of PVF in zebrafish eggs and embryos, and the maternal or zygotic origin of the identified proteins was studied. In silico analysis of PVF protein composition revealed an enrichment of protein classes associated with non-specific humoral innate immunity. We found lectins, protease inhibitors, transferrin, and glucosidases present from early embryogenesis until hatching. Finally, in vitro and in vivo experiments done with this fluid demonstrated that the PVF possessed a strong agglutinating capacity on bacterial cells and protected the embryos when challenged with the pathogenic bacteria Edwardsiella tarda. Our results suggest that the PVF is a primitive inherited immune extraembryonic system that protects the embryos from external biological threats prior to hatching.

Discovery of glycerol phosphate modification on streptococcal rhamnose polysaccharides

Cell wall glycopolymers on the surface of Gram-positive bacteria are fundamental to bacterial physiology and infection biology. Here we identify gacH, a gene in the Streptococcus pyogenes group A carbohydrate (GAC) biosynthetic cluster, in two independent transposon library screens for its ability to confer resistance to zinc and susceptibility to the bactericidal enzyme human group IIA-secreted phospholipase A₂. Subsequent structural and phylogenetic analysis of the GacH extracellular domain revealed that GacH represents an alternative class of glycerol phosphate transferase. We detected the presence of glycerol phosphate in the GAC, as well as the serotype c carbohydrate from Streptococcus mutans, which depended on the presence of the respective gacH homologs. Finally, nuclear magnetic resonance analysis of GAC confirmed that glycerol phosphate is attached to approximately 25% of the GAC N-acetylglucosamine side-chains at the C6 hydroxyl group. This previously unrecognized structural modification impacts host-pathogen interaction and has implications for vaccine design.

Structure and biological activities of a hexosamine-rich cell wall polysaccharide isolated from the probiotic Lactobacillus farciminis

Lactobacillus farciminis CIP 103136 is a bacterial strain with recognized probiotic properties. However, the mechanisms underlying such properties have only been partially elucidated. In this study, we isolated and purified a cell-wall associated polysaccharide (CWPS), and evaluated its biological role in vitro. The structure of CWPS and responses from stimulation of (i) human macrophage-like THP-1 cells, (ii) human embryonal kidney (HEK293) cells stably transfected with Toll-like receptors (TLR2 or TLR4) and (iii) human colonocyte-like T84 intestinal epithelial cells, upon exposure to CWPS were studied. The structure of the purified CWPS from L. farciminis CIP 103136 was analyzed by nuclear magnetic resonance (NMR), MALDI-TOF-TOF MS, and methylation analyses in its native form and following Smith degradation. It was shown to be a novel branched polysaccharide, composed of linear backbone of trisaccharide repeating units of: [→6αGlcpNAc1 → 4βManpNAc1 → 4βGlcpNAc1→] highly substituted with single residues of αGlcp, αGalp and αGlcpNAc. Subsequently, the lack of pro- or anti-inflammatory properties of CWPS was established on macrophage-like THP-1 cells. In addition, CWPS failed to modulate cell signaling pathways dependent of TLR2 and TLR4 in transfected HEK-cells. Finally, in T84 cells, CWPS neither influenced intestinal barrier integrity under basal conditions nor prevented TNF-α/IFN-γ cytokine-mediated epithelium impairment.

Another Brick in the Wall: a Rhamnan Polysaccharide Trapped inside Peptidoglycan of Lactococcus lactis

Polysaccharides are ubiquitous components of the Gram-positive bacterial cell wall. In Lactococcus lactis, a polysaccharide pellicle (PSP) forms a layer at the cell surface. The PSP structure varies among lactococcal strains; in L. lactis MG1363, the PSP is composed of repeating hexasaccharide phosphate units. Here, we report the presence of an additional neutral polysaccharide in L. lactis MG1363 that is a rhamnan composed of α-l-Rha trisaccharide repeating units. This rhamnan is still present in mutants devoid of the PSP, indicating that its synthesis can occur independently of PSP synthesis. High-resolution magic-angle spinning nuclear magnetic resonance (HR-MAS NMR) analysis of whole bacterial cells identified a PSP at the surface of wild-type cells. In contrast, rhamnan was detected only at the surface of PSP-negative mutant cells, indicating that rhamnan is located underneath the surface-exposed PSP and is trapped inside peptidoglycan. The genetic determinants of rhamnan biosynthesis appear to be within the same genetic locus that encodes the PSP biosynthetic machinery, except the gene tagO encoding the initiating glycosyltransferase. We present a model of rhamnan biosynthesis based on an ABC transporter-dependent pathway. Conditional mutants producing reduced amounts of rhamnan exhibit strong morphological defects and impaired division, indicating that rhamnan is essential for normal growth and division. Finally, a mutation leading to reduced expression of lcpA, encoding a protein of the LytR-CpsA-Psr (LCP) family, was shown to severely affect cell wall structure. In lcpA mutant cells, in contrast to wild-type cells, rhamnan was detected by HR-MAS NMR, suggesting that LcpA participates in the attachment of rhamnan to peptidoglycan.IMPORTANCE In the cell wall of Gram-positive bacteria, the peptidoglycan sacculus is considered the major structural component, maintaining cell shape and integrity. It is decorated with other glycopolymers, including polysaccharides, the roles of which are not fully elucidated. In the ovococcus Lactococcus lactis, a polysaccharide with a different structure between strains forms a layer at the bacterial surface and acts as the receptor for various bacteriophages that typically exhibit a narrow host range. The present report describes the identification of a novel polysaccharide in the L. lactis cell wall, a rhamnan that is trapped inside the peptidoglycan and covalently bound to it. We propose a model of rhamnan synthesis based on an ABC transporter-dependent pathway. Rhamnan appears as a conserved component of the lactococcal cell wall playing an essential role in growth and division, thus highlighting the importance of polysaccharides in the cell wall integrity of Gram-positive ovococci.

Structural investigation of cell wall polysaccharides of Lactobacillus delbrueckii subsp. bulgaricus 17

Lactobacilli are valuable strains for commercial (functional) food fermentations. Their cell surface-associated polysaccharides (sPSs) possess important functional properties, such as acting as receptors for bacteriophages (bacterial viruses), influencing autolytic characteristics and providing protection against antimicrobial peptides. The current report provides an elaborate molecular description of several surface carbohydrates of Lactobacillus delbrueckii subsp. bulgaricus strain 17. The cell surface of this strain was shown to contain short chain poly(glycerophosphate) teichoic acids and at least two different sPSs, designated here as sPS1 and sPS2, whose chemical structures were examined by 2D nuclear magnetic resonance spectroscopy and methylation analysis. Neutral branched sPS1, extracted with n-butanol, was shown to be composed of hexasaccharide repeating units (-[α-d-Glcp-(1-3)-]-4-β-l-Rhap2OAc-4-β-d-Glcp-[α-d-Galp-(1-3)]-4-α-Rhap-3-α-d-Galp-), while the major component of the TCA-extracted sPS2 was demonstrated to be a linear d-galactan with the repeating unit structure being (-[Gro-3P-(1-6)-]-3-β-Galf-3-α-Galp-2-β-Galf-6-β-Galf-3-β-Galp-).

Structural studies of the cell wall polysaccharides from three strains of Lactobacillus helveticus with different autolytic properties: DPC4571, BROI, and LH1

Lactobacillus helveticus is traditionally used in dairy industry as a starter or an adjunct culture for manufacture of cheese and some types of fermented milk. Its autolysis releases intracellular enzymes which is a prerequisite for optimum cheese maturation, and is known to be strain dependent. Autolysis is caused by an enzymatic hydrolysis of the cell wall peptidoglycan (PG) by endogenous peptidoglycan hydrolases (PGHs) or autolysins. Origins of differences in autolytic properties of different strains are not fully elucidated. Regulation of autolysis possibly depends on the structure of the cell wall components other than PG, particularly polysaccharides. In the present work, we screened six L. helveticus strains with different autolytic properties: DPC4571, BROI and LH1. We established, for the first time, that cell walls (CWs) of these strains contained polysaccharides, different from their CW teichoic acids. Cell wall polysaccharides of three strains were purified, and their chemical structures were established by 2D NMR spectroscopy and methylation analysis. The structures of their repeating units are presented.

L-rhamnose antigen: a promising alternative to α-gal for cancer immunotherapies

The targeting of autologous vaccines toward antigen presenting cells (APCs) via the in vivo complexation between anti α-Gal (anti-Gal) antibodies and α-Gal antigens presents a promising cancer immunotherapy with enhanced immunogenicity. This strategy takes advantage of the ubiquitous anti-Gal antibody in human serum. In contrast to the α-Gal epitope, the recent identification of high titers of anti-l-rhamnose (anti-Rha) antibodies in humans reveals a new approach toward immunotherapy employing l-rhamnose (Rha) monosaccharides. In order to evaluate this simple antigen in preclinical applications, we have synthesized Rha-conjugated immunogens and successfully induced high titers of anti-Rha antibodies in wildtype mice. Moreover, our studies demonstrate for the first time that wildtype mice could replace α1,3galactosyltransferase knockout (α1,3GT KO) mice in such antigen/antibody-mediated vaccine design when developing cancer immunotherapies.

A gene family of putative immune recognition molecules in the hydroid Hydractinia

Animal taxa display a wide array of immune-type receptors that differ in their specificities, diversity, and mode of evolution. These molecules ensure effective recognition of potential pathogens for subsequent neutralization and clearance. We have characterized a family of putative immune recognition molecules in the colonial hydroid Hydractinia symbiolongicarpus. A complementary DNA fragment with high similarity to the sea urchin L: -rhamnose-binding lectin was isolated and used to screen 9.5 genome equivalents of a H. symbiolongicarpus bacterial artificial chromosome library. One of the resulting 19 positive clones was sequenced and revealed the presence of a 5,111-bp gene organized in 13 exons and 12 introns. The gene was predicted to encode a 726-amino acid secreted modular protein composed of a signal peptide, an anonymous serine-rich domain, eight thrombospondin type 1 repeats, and a L: -rhamnose-binding lectin domain. The molecule was thus termed Rhamnospondin (Rsp). Southern hybridization and sequence analyses indicated the presence of a second Rsp gene. The cDNA from both Rsp genes was sequenced in 18 individuals, revealing high levels of genetic polymorphism. Nucleotide substitutions were distributed throughout the molecule and showed a significantly higher number of synonymous substitutions per synonymous sites than its nonsynonymous counterparts. Whole-mount in situ hybridization and semi-quantitative reverse transcription polymerase chain reaction of microorganism-challenged colonies indicated that Rsp molecules were specifically and constitutively expressed in the hypostome of gastrozooids' mouth. Thus, the combination of (1) comparative analysis on domain composition and function, (2) polymorphism, and (3) expression patterns, suggest that Rsp genes encode a family of putative immune recognition receptors, which may act by binding microorganisms invading the colony through the polyp's mouth.

Immunochemical study of polysaccharide antigen in Streptococcus sobrinus and Streptococcus downei with a cross-reactive monoclonal antibody

A monoclonal antibody (mAb h-448) was prepared after cell fusion of mouse myeloma cells (SP2/0-Ag-14) to the spleen cells of mice immunised with serotype h strain (MF25) of Streptococcus downei. The antibody (IgM class) reacted in enzyme immunoassay only with whole cells as well as purified polysaccharide (PS) antigen of Streptococcus sobrinus (types d and g) and Streptococcus downei (serotype h), but not with cells or purified PS antigen from any other serotypes of the mutans group of streptococci. mAb h-448 also quantitatively precipitated in solution with the purified antigens. Competitive hapten inhibition tests demonstrated that beta-methylgalactopyranoside inhibited the reaction most strongly. Although rhamnose also showed a substantial inhibitory effect, the results of this study indicate that the antigenic determinant of the PS antigen has a structure similar to the beta-methylgalactopyranoside molecule.

Cross-reactive polysaccharide antigens (types a, d, and h) of the mutans group of streptococci: different molecular forms of the type as distinguishable by monoclonal antibodies

As compared to the previous precipitin inhibition tests differences were found in the reactivities of monoclonal antibodies (MAbs), a-4 and a-84 with Streptococcus cricetus (serotype a) in an enzyme immunoassay using whole cells, purified cell wall antigen and haptenic sugars coated onto microtitre wells. Investigation into the differences led to the finding that the purified antigen from S. cricetus cells consisted mainly of three forms with different molecular weights and sugar contents. MAb a-4 reacted with a high molecular weight form (AgI, molecular weight of 46,000) and low molecular weight forms (AgII and AgIII, molecular weights of 9,800 and 20,000, respectively) whereas MAb a-84 reacted only with the high-molecular form. Gas chromatographic analysis revealed that all antigens contained rhamnose, galactose and glucose but in different ratios of the sugars. Although the binding site of AgII/AgIII with MAb a-4 seemed to be slightly different from that of AgI with MAb a-84, the predominant immunodeterminant of the antigens was considered to be the same. On the basis of these results, the chemical structures of the antigenic determinants are suggested. The nature of the antigen-antibody reactions is discussed.

Immunological study of cross-reactive polysaccharide antigens (types a, d, and h) of oral Streptococcus spp. with monoclonal antibodies

Two monoclonal antibodies against the cross-reactive antigens of S. cricetus (type a) and S. sobrinus (type d) were isolated. Galactose and especially melibiose inhibited the precipitin reaction markedly. Inhibition by melibiose was over 200-fold stronger than that by galactose. This may indicate that galactose-alpha 1, 6-glucose is the predominant antigenic determinant of this cross-reactive antigen. This antigen was also found in S. sobrinus type h strains, but no antigen was found in one type d strain (OMZ176).

Structural studies of the rhamnose-glucose polysaccharide antigen from Streptococcus sobrinus B13 and 6715-T2

The rhamnose-glucose polysaccharide antigens from the cell walls of Streptococcus sobrinus B13 and 6715-T2 (formerly Streptococcus mutans serotypes d and g, respectively) were structurally examined by using gas chromatography-mass spectroscopy. These data confirmed earlier chemical and serological studies suggesting that these polysaccharides had identical structures. The polysaccharides appeared to have a backbone of alternating 1,2- and 1,3-linked rhamnose units. Branching occurred at 1,2,3-linked rhamnose units. Side chains appeared to be composed of 1,2- and 1,6-linked glucose units with glucose as the only terminal carbohydrate.

Characterization of polysaccharide antigens of Streptococcus mutans B13 grown under various conditions

Bacteria may respond to changes in their environment by varying the synthesis of surface components. This study examined the effects of various culture conditions on two wall polysaccharides of Streptococcus mutans B13 (serotype d): serotype d antigen, a galactose-glucose polymer, and RGP antigen, a rhamnose-glucose polymer. Cells were grown in a chemostat at various dilution rates (D) and pH values, including D = 0.05, 0.1, and 0.5 h-1 at pH 6.0 and D = 0.1 h-1 at pH 5.5, 6.0, 6.5, and 7.5. The cells were examined for protein and carbohydrate content by colorimetric assays and gas-liquid chromatography. Rantz-Randall extracts (120 degrees C, 30 min) and M-1 N-acetylmuramidase digests were prepared and examined for the presence of specific antigens by agar gel diffusion and quantitative precipitation assays. Cell preparations did not vary significantly with respect to total protein or carbohydrate content; however, cells grown at D = 0.1 h-1 and pH 7.5 had a significantly higher rhamnose content than did the other preparations. Rapidly growing cultures appeared to be more resistant to M-1 N-acetylmuramidase digestion than did slower-growing cultures. Agar gel diffusion studies demonstrated that both serotype d and RGP antigens were present in all samples, although significantly less RGP antigen was noted in the pH 7.5 culture. These observations were confirmed by quantitative precipitation assays. M-1 N-acetylmuramidase digests of the pH 7.5 culture were lacking in RGP precipitation activity although RGP inhibition activity was demonstrated. The data suggest that the cell content of serotype d antigen was relatively constant under the growth conditions tested, whereas the synthesis of RGP antigen was modified under conditions of high pH.

Detection of antigens in enzymic lysates of cell wall from Streptococcus mutans strains

Lysis of cell wall preparations from strains representing serotypes a - g of Streptococcus mutans has provided a convenient and efficient means of obtaining the typing antigens in a soluble undegraded form, and has demonstrated that, in each case, the antigen is a cell wall component in the strict sense of a component joined covalently to peptidoglycan. This influences the choice of extraction procedures.

Characterization of serological cross-reactivity between polysaccharide antigens of Streptococcus mutans serotypes c and d

Immunological assays with antisera prepared against purified Streptococcus mutans serotype c polysaccharide demonstrated that a cross-reacting determinant on c polysaccharide reacted with the wall-associated rhamnose-glucose polysaccharide from S. mutans serotype d. Studies with 60 antisera prepared against chemostat cultures of S. mutans Ingbritt (c) demonstrated that the rhamnose-glucose polysaccharide cross-reactive determinant was consistently expressed on c antigen under a variety of growth conditions.

Purification and immunological characterization of a rhamnose-glucose antigen from Streptococcus mutans 6517-T2 (serotype g)

The serotype antigens of Streptococcus mutans have been described as cell wall-associated polysaccharides. In this study, an additional wall polysaccharide antigen was purified and characterized from S. mutans strain 6715-T2, a mutant of 6715 (serotype g). Strain 6715-T2 lost the serotype antigen during animal passage. Rhamnose-containing carbohydrate fractions were solubilized from bacterial cells by extraction with 5% trichloroacetic acid at 4 degrees C for 18 h and with 0.01 N HCl at 100 degrees C for 20 min. Extracts were combined and purified on columns of diethylaminoethyl-Sephadex A-25 and Sephadex G-100. The purified sample contained 59% rhamnose, 31% glucose, 2.2% protein, and 0.24% phosphorus. The purified rhamnose-glucose polysaccharide (RGP/6715-T2) reacted strongly with antisera to whole cells of 6715-T2. Agar gel diffusion and comparative immunoelectrophoresis studies revealed that RGP/6715-T2 was serologically distinct from the serotype g and d polysaccharide antigens. These techniques also indicated immunological identity between RGP/6715-T2 and RGP/B13, a rhamnose-glucose polymer previously isolated from S. mutans B13, a serotype d strain. Antigen immunologically identical to RGP/6715-T2 was detected both in Rantz-Randall extracts from whole cells of S. mutans strains 6715, OMZ-65, and 6715-PT and in extracts from cells of 6715-T2 and C307, two mutant serotype g strains that lacked the serotype g antigen.

Biology, immunology, and cariogenicity of Streptococcus mutans

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