Immune response profiling of primary monocytes and oral keratinocytes to different Tannerella forsythia strains and their cell surface mutants

The oral pathogen Tannerella forsythia possesses a unique surface (S-) layer with a complex O-glycan containing a bacterial sialic acid mimic in the form of either pseudaminic acid or legionaminic acid at its terminal position. We hypothesize that different T. forsythia strains employ these stereoisomeric sugar acids for interacting with the immune system and resident host tissues in the periodontium. Here, we show how T. forsythia strains ATCC 43037 and UB4 displaying pseudaminic acid and legionaminic acid, respectively, and selected cell surface mutants of these strains modulate the immune response in monocytes and human oral keratinocytes (HOK) using a multiplex immunoassay. When challenged with T. forsythia, monocytes secrete proinflammatory cytokines, chemokines and vascular endothelial growth factor (VEGF) with the release of interleukin-1β (IL-1β) and IL-7 being differentially regulated by the two T. forsythia wild-type strains. Truncation of the bacteria's O-glycan leads to significant reduction of IL-1β and regulates macrophage inflammatory protein-1. HOK infected with T. forsythia produce IL-1Ra, chemokines and VEGF. Although the two wild-type strains elicit preferential immune responses for IL-8, both truncation of the O-glycan and deletion of the S-layer result in significantly increased release of IL-8, granulocyte-macrophage colony-stimulating factor and monocyte chemoattractant protein-1. Through immunofluorescence and confocal laser scanning microscopy of infected HOK we additionally show that T. forsythia is highly invasive and tends to localize to the perinuclear region. This indicates, that the T. forsythia S-layer and attached sugars, particularly pseudaminic acid in ATCC 43037, contribute to dampening the response of epithelial tissues to initial infection and hence play a pivotal role in orchestrating the bacterium's virulence.

Characterization of an α-l-fucosidase from the periodontal pathogen Tannerella forsythia

The periodontal pathogen Tannerella forsythia expresses several glycosidases which are linked to specific growth requirements and are involved in the invasion of host tissues. α-l-Fucosyl residues are exposed on various host glycoconjugates and, thus, the α-l-fucosidases predicted in the T. forsythia ATCC 43037 genome could potentially serve roles in host-pathogen interactions. We describe the molecular cloning and characterization of the putative fucosidase TfFuc1 (encoded by the bfo_2737 = Tffuc1 gene), previously reported to be present in an outer membrane preparation. In terms of sequence, this 51-kDa protein is a member of the glycosyl hydrolase family GH29. Using an artificial substrate, p-nitrophenyl-α-fucose (KM 670 μM), the enzyme was determined to have a pH optimum of 9.0 and to be competitively inhibited by fucose and deoxyfuconojirimycin. TfFuc1 was shown here to be a unique α(1,2)-fucosidase that also possesses α(1,6) specificity on small unbranched substrates. It is active on mucin after sialidase-catalyzed removal of terminal sialic acid residues and also removes fucose from blood group H. Following knock-out of the Tffuc1 gene and analyzing biofilm formation and cell invasion/adhesion of the mutant in comparison to the wild-type, it is most likely that the enzyme does not act extracellularly. Biochemically interesting as the first fucosidase in T. forsythia to be characterized, the biological role of TfFuc1 may well be in the metabolism of short oligosaccharides in the periplasm, thereby indirectly contributing to the virulence of this organism. TfFuc1 is the first glycosyl hydrolase in the GH29 family reported to be a specific α(1,2)-fucosidase.

Outer membrane vesicles of Tannerella forsythia: biogenesis, composition, and virulence

Tannerella forsythia is the only ‘red‐complex’ bacterium covered by an S‐layer, which has been shown to affect virulence. Here, outer membrane vesicles (OMVs) enriched with putative glycoproteins are described as a new addition to the virulence repertoire of T. forsythia. Investigations of this bacterium are hampered by its fastidious growth requirements and the recently discovered mismatch of the available genome sequence (92A2 = ATCC BAA‐2717) and the widely used T. forsythia strain (ATCC 43037). T. forsythia was grown anaerobically in serum‐free medium and biogenesis of OMVs was analyzed by electron and atomic force microscopy. This revealed OMVs with a mean diameter of ~100 nm budding off from the outer membrane while retaining the S‐layer. An LC‐ESI‐TOF/TOF proteomic analysis of OMVs from three independent biological replicates identified 175 proteins. Of these, 14 exhibited a C‐terminal outer membrane translocation signal that directs them to the cell/vesicle surface, 61 and 53 were localized to the outer membrane and periplasm, respectively, 22 were predicted to be extracellular, and 39 to originate from the cytoplasm. Eighty proteins contained the Bacteroidales O‐glycosylation motif, 18 of which were confirmed as glycoproteins. Release of pro‐inflammatory mediators from the human monocytic cell line U937 and periodontal ligament fibroblasts upon stimulation with OMVs followed a concentration‐dependent increase that was more pronounced in the presence of soluble CD14 in conditioned media. The inflammatory response was significantly higher than that caused by whole T. forsythia cells. Our study represents the first characterization of T. forsythia OMVs, their proteomic composition and immunogenic potential.

The S-layer proteins of Tannerella forsythia are secreted via a type IX secretion system that is decoupled from protein O-glycosylation

Conserved C-terminal domains (CTD) have been shown to act as a signal for the translocation of certain proteins across the outer membrane of Bacteroidetes via a type IX secretion system (T9SS). The genome sequence of the periodontal pathogen Tannerella forsythia predicts the presence of the components for a T9SS in conjunction with a suite of CTD proteins. T. forsythia is covered with a two-dimensional crystalline surface (S-) layer composed of the glycosylated CTD proteins TfsA and TfsB. To investigate, if T9SS is functional in T. forsythia, T9SS-deficient mutants were generated by targeting either TF0955 (putative C-terminal signal peptidase) or TF2327 (PorK ortholog), and the mutants were analyzed with respect to secretion, assembly and glycosylation of the S-layer proteins as well as proteolytic processing of the CTD and biofilm formation. In either mutant, TfsA and TfsB were incapable of translocation, as evidenced by the absence of the S-layer in transmission electron microscopy of ultrathin-sectioned bacterial cells. Despite being entrapped within the periplasm, mass spectrometry analysis revealed that the S-layer proteins were modified with the complete, mature glycan found on the secreted proteins, indicating that protein translocation and glycosylation are two independent processes. Further, the T9SS mutants showed a denser biofilm with fewer voids compared with the wild-type. This study demonstrates the functionality of T9SS and the requirement of CTD for the outer membrane passage of extracellular proteins in T. forsythia, exemplified by the two S-layer proteins. In addition, T9SS protein translocation is decoupled from O-glycan attachment in T. forsythia.

Potential of the Tannerella forsythia S-layer to delay the immune response

The periodontal pathogen Tannerella forsythia possesses a glycosylated S-layer as an outermost cell decoration. While the S-layer provides a selection advantage to the bacterium in the natural habitat, its virulence potential remains to be investigated. In the present study, the immune responses of human macrophages and gingival fibroblasts upon stimulation with wild-type T. forsythia and an S-layer-deficient mutant were investigated. The mRNA expression levels of the pro-inflammatory mediators IL-1β, TNF-α, and IL-8 were analyzed by qPCR, and the production of the corresponding cytokines was investigated by ELISA. The S-layer-deficient T. forsythia mutant induced significantly higher levels of pro-inflammatory mediators compared with wild-type T. forsythia, especially at the early phase of response. Analysis of these data suggests that the S-layer of T. forsythia is an important virulence factor that attenuates the host immune response to this pathogen by evading the bacterium's recognition by the innate immune system.

ABBREVIATIONS

DMSO, dimethylsulfoxide; FBS, fetal bovine serum; GAPDH, glycerinaldehyde-3-phosphate-dehydrogenase; HGFs, human gingival fibroblasts; LPS, lipopolysaccharide; MEM, minimal essential medium; MTT, 3,4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide; OD, optical density; PBS, phosphate-buffered saline; qPCR, quantitative polymerase chain-reaction; SD, standard deviation; Tannerella forsythia ATCC 43037, Tf wt; Tannerella forsythia ATCC 43037 S-layer mutant, Tf ΔtfsAB.

Glycobiology of surface layer proteins

Over the last two decades, a significant change of perception has taken place regarding prokaryotic glycoproteins. For many years, protein glycosylation was assumed to be limited to eukaryotes; but now, a wealth of information on structure, function, biosynthesis and molecular biology of prokaryotic glycoproteins has accumulated, with surface layer (S-layer) glycoproteins being one of the best studied examples. With the designation of Archaea as a second prokaryotic domain of life, the occurrence of glycosylated S-layer proteins had been considered a taxonomic criterion for differentiation between Bacteria and Archaea. Extensive structural investigations, however, have demonstrated that S-layer glycoproteins are present in both domains. Among Gram-positive bacteria, S-layer glycoproteins have been identified only in bacilli. In Gram-negative organisms, their presence is still not fully investigated; presently, there is no indication for their existence in this class of bacteria. Extensive biochemical studies of the S-layer glycoprotein from Halobacterium halobium have, at least in part, unravelled the glycosylation pathway in Archaea; molecular biological analyses of these pathways have not been performed, so far. Significant observations concern the occurrence of unusual linkage regions both in archaeal and bacterial S-layer glycoproteins. Regarding S-layer glycoproteins of bacteria, first genetic data have shed some light into the molecular organization of the glycosylation machinery in this domain. In addition to basic S-layer glycoprotein research, the biotechnological application potential of these molecules has been explored. With the development of straightforward molecular biological methods, fascinating possibilities for the expression of prokaryotic glycoproteins will become available. S-layer glycoprotein research has opened up opportunities for the production of recombinant glycosylation enzymes and tailor-made S-layer glycoproteins in large quantities, which are commercially not yet available. These bacterial systems may provide economic technologies for the production of biotechnologically and medically important glycan structures in the future.

Purification and structure elucidation of the N-acetylbacillosamine-containing polysaccharide from Bacillus licheniformis ATCC 9945

The exopolysaccharide of Bacillus licheniformis ATCC 9945 (formerly B. subtilis ATCC 9945) contains among other glycoses 4-acetamido-2-amino-2,4,6-trideoxy-D-glucose, termed N-acetylbacillosamine (Bac2N4NAc). A similar diamino glycose, 2-acetamido-4-amino-2,4,6-trideoxy-D-glucose, was found in a surface layer (S-layer) glycoprotein preparation of Clostridium symbiosum HB25. Electron microscopic studies, however, showed that B. licheniformis ATCC 9945 is not covered with an S-layer lattice, indicating that the N-acetylbacillosamine present in that organism might be a constituent of a cell wall-associated polymer. For elucidation of the structure of the N-acetylbacillosamine-containing polysaccharide, it was purified from a trichloroacetic acid extract of B. licheniformis ATCC 9945 cells. Using different hydrolysis protocols and a hydrolysate of the S-layer glycoprotein preparation from C. symbiosum HB25 as reference, the purified polysaccharide was found to contain 2,4-diamino-2,4,6-trideoxy-glucose, 2-acetamido-2-deoxy-glucose, 2-acetamido-2-deoxy-galactose and galactose in a molar ratio of 1 : 1 : 1 : 2. One- and two-dimensional NMR spectroscopy, including 800 MHz proton magnetic resonance measurements, in combination with chemical modification and degradation experiments, revealed that the polysaccharide consists of identical pyruvylated pentasaccharide repeating units with the structure: [-->3)-[(S)Py-(3,4)-beta-D-Galp-(1-->6)]-alpha-D-GlcpNAc-(1-->3)-beta-D-Bacp2N4NAc-(1-->3)-[(S)Py-(3,4)-beta-D-Galp-(1-->6)]-beta-D-GalpNAc-(1-->](n)

Prokaryotic glycosylation

With the advances of molecular biology and with improved analytical techniques a significant change of perception has taken place regarding prokaryotic glycoproteins. Glycosylation of proteins from prokaryotes is no longer considered a specific feature of certain organisms but has been demonstrated for many archaea and bacteria. Besides the occurrence of glycosylated enzymes, antigens and other cell envelope components, surface layer (S-layer) glycoproteins represent the best-studied examples of glycosylated prokaryotic proteins. They are widely distributed among archaeal wild-type strains, but among bacteria they have been mainly observed with Gram-positive organisms. There is, in general, an enormous increase of reports on the presence of glycosylated proteins among prokaryotes. For their isolation and characterization a great number of methods are available, aiming at the identification of the covalent linkage between the carbohydrate and the polypeptide portion. So far, several differences in structure and biosynthesis have been observed in comparison to eukaryotic glycoproteins. In this review we introduce a protocol which has been successfully applied to the investigation of the complex structures, linkage units, and polypeptide consensus sequences of glycosylated bacterial S-layer proteins.

A pyrophosphate bridge links the pyruvate-containing secondary cell wall polymer of Paenibacillus alvei CCM 2051 to muramic acid

The peptidoglycan, the secondary cell wall polymer (SCWP), and the surface layer (S-layer) glycoprotein are the major glycosylated cell wall components of Paenibacillus alvei CCM 2051. In this report, the complete structure of the SCWP, its linkage to the peptidoglycan layer, and its physicochemical properties have been investigated. From the combined evidence of chemical and structural analyses together with one- and two-dimensional nuclear magnetic resonance spectroscopy, the following structure of the SCWP-peptidoglycan complex is proposed: [(Pyr4,6)-beta-D-ManpNAc-(1-->4)-beta-D-GlcpNAc-(1-->3)]n-11-(Pyr4,6)-beta-D-ManpNAc-(1-->4)-alpha-D-GlcpNAc-(1-->O)-PO2-O-PO2-(O-->6)-MurNAc- Each disaccharide unit is substituted by 4,6-linked pyruvic acid residues. Under mild acidic conditions, up to 50% of them are lost, leaving non-substituted ManNAc residues. The anionic glycan chains constituting the SCWP are randomly linked via pyrophosphate groups to C-6 of muramic acid residues of the peptidoglycan layer. 31P NMR reveals two signals that, as a consequence of micelle formation, experience different line broadening. Therefore, their integral ratio deviates significantly from 1:1. By treatment with ethylenediaminetetraacetic acid, sodium dodecyl sulfate, and sonication immediately prior to NMR measurement, this ratio approaches unity. The reversibility of this behavior corroborates the presence of a pyrophosphate linker in this SCWP-peptidoglycan complex. In addition to the determination of the structure and linkage of the SCWP, a possible scenario for its biological function is discussed.

A novel type of carbohydrate-protein linkage region in the tyrosine-bound S-layer glycan of Thermoanaerobacterium thermosaccharolyticum D120-70

The surface-layer (S-layer) protein of Thermoanaerobacterium thermosaccharolyticum D120-70 contains glycosidically linked glycan chains with the repeating unit structure -->4)[alpha-D-Galp-(1-->2)]-alpha-L-Rhap-(1-->3)[beta-D-Glcp-(1--> 6)] -beta-D-Manp-(1-->4)-alpha-L-Rhap-(1-->3)-alpha-D-Glcp-(1--> . After proteolytic degradation of the S-layer glycoprotein, three glycopeptide pools were isolated, which were analyzed for their carbohydrate and amino-acid compositions. In all three pools, tyrosine was identified as the amino-acid constituent, and the carbohydrate compositions corresponded to the above structure. Native polysaccharide PAGE showed the specific heterogeneity of each pool. For examination of the carbohydrate-protein linkage region, the S-layer glycan chain was partially hydrolyzed with trifluoroacetic acid. 1D and 2D NMR spectroscopy, including a novel diffusion-edited difference experiment, showed the O-glycosidic linkage region beta-D-glucopyranose-->O-tyrosine. No evidence was found of additional sugars originating from a putative core region between the glycan repeating units and the S-layer polypeptide. For the determination of chain-length variability in the S-layer glycan, the different glycopeptide pools were investigated by matrix-assisted laser desorption ionization-time of flight mass spectrometry, revealing that the degree of polymerization of the S-layer glycan repeats varied between three and 10. All masses were assigned to multiples of the repeating units plus the peptide portion. This result implies that no core structure is present and thus supports the data from the NMR spectroscopy analyses. This is the first observation of a bacterial S-layer glycan without a core region connecting the carbohydrate moiety with the polypeptide portion.

Are S-layer glycoproteins and lipopolysaccharides related?

Several glycan structures of S-layer glycoproteins of gram-positive eubacteria were compared with the principal structural organization of O-antigens of lipopolysaccharides of gram-negative eubacteria. Further, activated intermediates of the biosynthetic pathway of S-layer glycans were compared with activated intermediates of the route of assembly of lipopolysaccharide O-antigens. As a result, at least structural similarities between both types of molecules have been clearly observed. More detailed studies of the assembly of S-layer glycans are required to unambiguously demonstrate the extent to which the biosynthetic pathways of both molecules are related.

Individual-based prediction of the size of the supporting zones in the permanent dentition. A comparison of the Moyers method with a unitary prediction value

The aims of this individual-based study were 1. to assess the actual space requirements of the permanent canines and premolars, 2. to test the reliability of the Moyers method in predicting a space deficiency at the 75% confidence level and 3. to try to find a reliable unitary prediction value (= unitary value) as a possible substitute for the calculated Moyers values. Dental cast measurements were taken of the permanent dentition of 100 females and 100 males. The average sum of the widths of the maxillary and mandibular permanent canines and premolars was 20.8 mm (17.3 to 24.3 mm). The Moyers method could predict a maxillary space deficiency in 77.5% and a mandibular space deficiency in 65.5% of the subjects. The unitary value of 22.0 mm made it possible to predict a space deficiency in 83.5% of the subjects. The unitary value thus had a higher confidence level (83.5%) than the 75% level stated by Moyers and might thus substitute the calculated Moyers values. Furthermore, the unitary value is easy and quick to handle.

Complete glycan structure of the S-layer glycoprotein of Aneurinibacillus thermoaerophilus GS4-97

Isolate GS4-97 was purified from an extraction juice sample of an Austrian beet sugar factory and affiliated to the newly described species Aneurinibacillus thermoaerophilus. It is closely related to the type strain of this species, A.thermoaerophilus L420-91(T), and possesses a square surface layer (S-layer) array composed of identical glycoprotein monomers as its outermost cell envelope component. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the purified S-layer showed an apparent molecular mass of approximately 109,000. After thorough proteolytic degradation of this material by pronase E and purification of the reaction mixture by gel permeation, chromatofocusing, and reversed-phase chromatography, a homogeneous glycopeptide fraction was obtained which was subjected to one- and two-dimensional nuclear magnetic resonance spectroscopy. The combined chemical and spectroscopic evidence, together with N-terminal sequencing, suggest the following structure of the O-glycosidically linked S-layer glycan chain of the glycopeptide: This is the first description of a beta-d-GalNAc-Thr linkage in glycoproteins.

[Proprioceptive abilities of surgically and conservatively treated knee joints with injuries of the cruciate ligament]

In the present study we evaluated proprioceptive capabilities of the knee joint with a balance test and correlated these findings to parameters which document mechanical stability. We compared 8 conservatively treated and 12 surgically treated patients with ACL-deficient knee joints with a control group of 12 subjects. The balance test was performed with a Kistler force plate. Both the conservatively treated and the surgically treated patients showed significantly higher deviations of their centre of gravity than the control group. This was true not only for the injured leg but also for the noninjured contralateral leg. The differences were most remarkable when comparing the entire distance of centre of gravity deviations during 10 s. Additionally, the conservatively treated patients interrupted the test procedure significantly more frequently than the other two groups. We were not able to document any correlation between proprioceptive function and parameters for joint stability such as anterior drawer, Lachman, pivot shift and KT-1000 measurements.

CLINICAL SIGNIFICANCE

In patients with conservatively or surgically treated ACL tears the rehabilitation of proprioceptive capabilities is mandatory both for the injured leg and for the noninjured contralateral leg in order to restore the function of the lower extremities. Reconstruction of passive stability alone is not sufficient.

Biochemistry of S-layers

During evolution prokaryotes have developed different envelope structures exterior to the cell wall proper. Among these surface components are regularly arranged S-layers and capsules. The structural characterization and the detailed chemical analysis of these surface molecules is a prerequisite to understand their biosynthesis and functional role(s) at the molecular level. Of particular interest are the glycosylated S-layer proteins which belong to the first prokaryotic glycoproteins ever described. Their characterization was performed on strains belonging to the thermophilic Bacillaceae and included structural studies and experiments to learn about the pathways for the glycan biosynthesis of S-layer glycoproteins. As an example for non-glycosylated S-layer proteins those of Lactobacillus helveticus strains are described in detail. Recently, a novel type of bacterial glycoconjugate was observed in the cell envelope of the extremely halophilic archaeon Natronococcus occultus which consists of a glycosylated polyglutamyl polymer. Beside the conventional biochemical techniques for the analysis new sophisticated instrumental methods such as X-ray photoelectron spectroscopy and matrix-assisted laser desorption ionization or electrospray ionization mass spectrometry have been introduced for the analysis of the protein and glycan portions of these cell surface macromolecules.

Characterization of the glycan structure of a major glycopeptide from the surface layer glycoprotein of Clostridium thermosaccharolyticum E207-71

The squarely arranged surface layer (S-layer) glycoprotein of Clostridium thermosaccharolyticum E207-71 was isolated from bacterial cells which were grown under defined culture conditions. By sodium dodecyl sulfate polyacrylamide gel electrophoresis, the S-layer showed a series of distinct bands with apparent molecular masses in the range 83-210 kDa. Upon deglycosylation by trifluoromethanesulfonic acid, only the single band at 83 kDa remained unchanged. After pronase digestion of the intact S-layer glycoprotein, the degradation products were isolated by gel-permeation chromatography, cation-exchange chromatography and isoelectric focusing. Three main fractions and an amino sugar containing minor fraction were obtained. The main fractions, which showed identical carbohydrate compositions, were further purified by reverse-phase chromatography and characterized by monosaccharide analysis, Smith degradation, methylation analysis, and one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy. The combined chemical and spectroscopical evidence suggest the following glycan structure for the main fractions: [Sequence: See text]

Accurate determination of the molecular weight of the major surface layer protein isolated from Clostridium thermosaccharolyticum by time-of-flight mass spectrometry

Matrix-assisted laser desorption with concomitant ionization, in combination with a linear time-of-flight mass spectrometer, was used to analyze underivatized and hard-to-solubilize surface layer proteins and glycoproteins by depositing them on top of a microcrystalline layer of the matrix alpha-cyano-4-hydroxycinnamic acid. Use of this special sample preparation technique allowed the first successful desorption-ionization of intact surface layer proteins and accurate determination of their molecular weights by mass spectrometry. The molecular mass of the monomeric subunit of the major surface layer protein isolated from Clostridium thermosaccharolyticum E207-71 was determined to be 75,621 +/- 81 Da. The obtainable mass accuracy of the technique is conservatively considered to be within +/- 0.2%. This result deviates from that given by sodium dodecyl sulfate-polyacrylamide gel electrophoresis by approximately 7.4 kDa because this method is strongly affected and biased by the three-dimensional structure of this type of surface protein. With the apparent advantages of unsurpassed mass accuracy, low dependence on the physicochemical properties of the surface layer proteins, and high sensitivity, it can be concluded that a linear time-of-flight instrument combined with UV matrix-assisted laser desorption with concomitant ionization is better suited for molecular weight determination than is gel electrophoresis.