News

group leader: Dr. Titz

Recent Submissions

  • Pathoblockers or antivirulence drugs as a new option for the treatment of bacterial infections

    Calvert, Matthew B; Jumde, Varsha R; Titz, Alexander
    The rapid development of antimicrobial resistance is threatening mankind to such an extent that the World Health Organization expects more deaths from infections than from cancer in 2050 if current trends continue. To avoid this scenario, new classes of anti-infectives must urgently be developed. Antibiotics with new modes of action are needed, but other concepts are also currently being pursued. Targeting bacterial virulence as a means of blocking pathogenicity is a promising new strategy for disarming pathogens. Furthermore, it is believed that this new approach is less susceptible towards resistance development. In this review, recent examples of anti-infective compounds acting on several types of bacterial targets, e.g., adhesins, toxins and bacterial communication, are described.
  • Efficient Two Step β-Glycoside Synthesis from -Acetyl -Glucosamine: Scope and Limitations of Copper(II) Triflate-Catalyzed Glycosylation

    Sommer, Roman; Hauck, Dirk; Titz, Alexander; HIPS, Helmholtz-Institute für pharmazeutische Forschung Saarland, Universitätscampus E8.1, 66123 Saarbrücken, Germany.
    β‐Linked glycosides of N‐acetyl glucosamine are widespread in nature. Their direct synthesis is hampered by the low reactivity of GlcNAc as a glycosyl donor. We report a selective and rapid copper(II) triflate‐catalyzed two‐step synthesis of β‐glycosides of GlcNAc from cheap GlcNAc as starting material without purification of intermediates. α‐Specific glycosylation can be achieved by increasing the amount of catalyst and extending reaction times.
  • Crystal Structures of Fungal Tectonin in Complex with O-Methylated Glycans Suggest Key Role in Innate Immune Defense.

    Sommer, Roman; Makshakova, Olga N; Wohlschlager, Therese; Hutin, Stephanie; Marsh, May; Titz, Alexander; Künzler, Markus; Varrot, Annabelle; HIPS, Helmholtz-Institut für pharmazeutische Forschung Saarland, Universitätscampus 8.1, 66123 Saarbrücken, Germany. (2018-03-06)
    Innate immunity is the first line of defense against pathogens and predators. To initiate a response, it relies on the detection of invaders, where lectin-carbohydrate interactions play a major role. O-Methylated glycans were previously identified as non-self epitopes and conserved targets for defense effector proteins belonging to the tectonin superfamily. Here, we present two crystal structures of Tectonin 2 from the mushroom Laccaria bicolor in complex with methylated ligands, unraveling the molecular basis for this original specificity. Furthermore, they revealed the formation of a ball-shaped tetramer with 24 binding sites distributed at its surface, resembling a small virus capsid. Based on the crystal structures, a methylation recognition motif was identified and found in the sequence of many tectonins from bacteria to human. Our results support a key role of tectonins in innate defense based on a distinctive and conserved type of lectin-glycan interaction.
  • N-Acetylmuramic Acid (MurNAc) Auxotrophy of the Oral PathogenTannerella forsythia: Characterization of a MurNAc Kinase and Analysis of Its Role in Cell Wall Metabolism.

    Hottmann, Isabel; Mayer, Valentina M T; Tomek, Markus B; Friedrich, Valentin; Calvert, Matthew B; Titz, Alexander; Schäffer, Christina; Mayer, Christoph; HIPS, Helmholtz-Institut für pharmazeutische Forschung Saarland, Universitätscampus 8.1, 66123 Saarbrücken, Germany. (2018)
    Tannerella forsythia is an anaerobic, Gram-negative oral pathogen that thrives in multispecies gingival biofilms associated with periodontitis. The bacterium is auxotrophic for the commonly essential bacterial cell wall sugarN-acetylmuramic acid (MurNAc) and, thus, strictly depends on an exogenous supply of MurNAc for growth and maintenance of cell morphology. A MurNAc transporter (Tf_MurT; Tanf_08375) and an ortholog of theEscherichia colietherase MurQ (Tf_MurQ; Tanf_08385) converting MurNAc-6-phosphate to GlcNAc-6-phosphate were recently described forT. forsythia.In between the respective genes on theT. forsythiagenome, a putative kinase gene is located. In this study, the putative kinase (Tf_MurK; Tanf_08380) was produced as a recombinant protein and biochemically characterized. Kinetic studies revealed Tf_MurK to be a 6-kinase with stringent substrate specificity for MurNAc exhibiting a 6 × 104-fold higher catalytic efficiency (kcat/Km) for MurNAc than forN-acetylglucosamine (GlcNAc) withkcatvalues of 10.5 s-1and 0.1 s-1andKmvalues of 200 μM and 116 mM, respectively. The enzyme kinetic data suggest that Tf_MurK is subject to substrate inhibition (Ki[S]= 4.2 mM). To assess the role of Tf_MurK in the cell wall metabolism ofT. forsythia, a kinase deletion mutant (ΔTf_murK::erm) was constructed. This mutant accumulated MurNAc intracellularly in the exponential phase, indicating the capability to take up MurNAc, but inability to catabolize MurNAc. In the stationary phase, the MurNAc level was reduced in the mutant, while the level of the peptidoglycan precursor UDP-MurNAc-pentapeptide was highly elevated. Further, according to scanning electron microscopy evidence, theΔTf_murK::ermmutant was more tolerant toward low MurNAc concentration in the medium (below 0.5 μg/ml) before transition from healthy, rod-shaped to fusiform cells occurred, while the parent strain required > 1 μg/ml MurNAc for optimal growth. These data reveal thatT. forsythiareadily catabolizes exogenous MurNAc but simultaneously channels a proportion of the sugar into peptidoglycan biosynthesis. Deletion ofTf_murKblocks MurNAc catabolism and allows the direction of MurNAc solely to peptidoglycan biosynthesis, resulting in a growth advantage in MurNAc-depleted medium. This work increases our understanding of theT. forsythiacell wall metabolism and may pave new routes for lead finding in the treatment of periodontitis.
  • An efficient synthesis of 1,6-anhydro- N -acetylmuramic acid from N -acetylglucosamine

    Calvert, Matthew B; Mayer, Christoph; Titz, Alexander; Helmholtz Institut für pharmazeutische Forschung Saarland, Universitätscampus E8.1, 66123 Saarbrücken, Germany. (2017-12-11)
  • Covalent Lectin Inhibition and Application in Bacterial Biofilm Imaging.

    Wagner, Stefanie; Hauck, Dirk; Hoffmann, Michael; Sommer, Roman; Joachim, Ines; Müller, Rolf; Imberty, Anne; Varrot, Annabelle; Titz, Alexander; HIPS, Helmholtz-Institut für pharmazeutische Forchung Saarland, Universitätscampus E8.1, 66123 Saarbrücken, Germany. (2017-09-28)
    Biofilm formation by pathogenic bacteria is a hallmark of chronic infections. In many cases, lectins play key roles in establishing biofilms. The pathogen Pseudomonas aeruginosa often exhibiting various drug resistances employs its lectins LecA and LecB as virulence factors and biofilm building blocks. Therefore, inhibition of the function of these proteins is thought to have potential in developing "pathoblockers" preventing biofilm formation and virulence. A covalent lectin inhibitor specific to a carbohydrate binding site is described for the first time. Its application in the LecA-specific in vitro imaging of biofilms formed by P. aeruginosa is also reported.
  • Photorhabdus luminescens lectin A (PllA) - a new probe for detecting α-galactoside-terminating glycoconjugates.

    Beshr, Ghamdan; Sikandar, Asfandyar; Jemiller, Eva-Maria; Klymiuk, Nikolai; Hauck, Dirk; Wagner, Stefanie; Wolf, Eckhard; Koehnke, Jesko; Titz, Alexander; Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Universitycampus E8.1, 66123 Saarbrücken, Germany. (2017-09-28)
    Lectins play important roles in infections by pathogenic bacteria, for example, in host colonization, persistence and biofilm formation. The Gram-negative entomopathogenic bacterium Photorhabdus luminescens symbiotically lives in insect-infecting Heterorhabditis nematodes and kills the insect host upon invasion by the nematode. The P. luminescens genome harbors the gene plu2096 coding for a novel lectin that we named PllA. We analyzed the binding properties of purified PllA with a glycan array and a binding assay in solution. Both assays revealed a strict specificity of PllA for alpha-galactoside-terminating glycoconjugates. The crystal structures of apo PllA and complexes with three different ligands revealed the molecular basis for the strict specificity of this lectin. Furthermore, we found that a 90 degree twist in subunit orientation leads to a peculiar quaternary structure compared with that of its ortholog LecA from Pseudomonas aeruginosa. We also investigated the utility of PllA as a probe for detecting alpha-galactosides. The alpha-Gal epitope is present on wild-type pig cells and the main reason for hyperacute organ rejection in pig to primate xenotransplantation. We noted that PllA specifically recognizes this epitope on the glycan array and demonstrated that PllA can be used as a fluorescent probe to detect this epitope on primary porcine cells in vitro. In summary, our biochemical and structural analyses of the P. luminescens lectin PllA have disclosed the structural basis for PllAs high specificity for alpha-galactoside-containing ligands, and we show that PllA can be used to visualize alpha-Gal epitope on porcine tissues.
  • Ciprofloxacin-loaded lipid-core nanocapsules as mucus penetrating drug delivery system intended for the treatment of bacterial infections in cystic fibrosis.

    Torge, Afra; Wagner, Stefanie; Chaves, Paula S; Oliveira, Edilene G; Guterres, Silvia S; Pohlmann, Adriana R; Titz, Alexander; Schneider, Marc; Beck, Ruy C R; Helmholtz Institut für pharmazeutische Forschung Saarland, Universitätscampus E8.1, 66123 Saarbrücken, Germany. (2017-05-10)
    Treatment of bacterial airway infections is essential for cystic fibrosis therapy. However, effectiveness of antibacterial treatment is limited as bacteria inside the mucus are protected from antibiotics and immune response. To overcome this biological barrier, ciprofloxacin was loaded into lipid-core nanocapsules (LNC) for high mucus permeability, sustained release and antibacterial activity. Ciprofloxacin-loaded LNC with a mean size of 180nm showed a by 50% increased drug permeation through mucus. In bacterial growth assays, the drug in the LNC had similar minimum inhibitory concentrations as the free drug in P. aeruginosa and S. aureus. Interestingly, formation of biofilm-like aggregates, which were observed for S. aureus treated with free ciprofloxacin, was avoided by exposure to LNC. With the combined advantages over the non-encapsulated drug, ciprofloxacin-loaded LNC represent a promising drug delivery system with the prospect of an improved antibiotic therapy in cystic fibrosis.
  • O-Alkylated heavy atom carbohydrate probes for protein X-ray crystallography: Studies towards the synthesis of methyl 2-O-methyl-L-selenofucopyranoside.

    Sommer, Roman; Hauck, Dirk; Varrot, Annabelle; Imberty, Anne; Künzler, Markus; Titz, Alexander; Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS),Saarland Universitätscampus E8.1, 66123 Saarbrücken, Germany. (2016)
    Selenoglycosides are used as reactive glycosyl donors in the syntheses of oligosaccharides. In addition, such heavy atom analogs of natural glycosides are useful tools for structure determination of their lectin receptors using X-ray crystallography. Some lectins, e.g., members of the tectonin family, only bind to carbohydrate epitopes with O-alkylated ring hydroxy groups. In this context, we report the first synthesis of an O-methylated selenoglycoside, specifically methyl 2-O-methyl-L-selenofucopyranoside, a ligand of the lectin tectonin-2 from the mushroom Laccaria bicolor. The synthetic route required a strategic revision and further optimization due to the intrinsic lability of alkyl selenoglycosides, in particular for the labile fucose. Here, we describe a successful synthetic access to methyl 2-O-methyl-L-selenofucopyranoside in 9 linear steps and 26% overall yield starting from allyl L-fucopyranoside.
  • Development of a competitive binding assay for the Burkholderia cenocepacia lectin BC2L-A and structure activity relationship of natural and synthetic inhibitors

    Beshr, Ghamdan; Sommer, Roman; Hauck, Dirk; Siebert, David Chan Bodin; Hofmann, Anna; Imberty, Anne; Titz, Alexander (2016)
  • The virulence factor LecB varies in clinical isolates: consequences for ligand binding and drug discovery

    Sommer, Roman; Wagner, Stefanie; Varrot, Annabelle; Nycholat, Corwin M.; Khaledi, Ariane; Häussler, Susanne; Paulson, James C.; Imberty, Anne; Titz, Alexander (2016)
  • Cinnamide Derivatives of d -Mannose as Inhibitors of the Bacterial Virulence Factor LecB from Pseudomonas aeruginosa

    Sommer, Roman; Hauck, Dirk; Varrot, Annabelle; Wagner, Stefanie; Audfray, Aymeric; Prestel, Andreas; Möller, Heiko M.; Imberty, Anne; Titz, Alexander; Helmholtz Institute for Pharmaceutical Research Saarland (HIPS);Saarland University, Building A4.1, 66123 Saarbruecken, Germany.; Chemical Biology of Carbohydrates; Helmholtz Institute for Pharmaceutical Research Saarland (HIPS); Universitätsstrasse 10 66123 Saarbrücken Germany; Chemical Biology of Carbohydrates; Helmholtz Institute for Pharmaceutical Research Saarland (HIPS); Universitätsstrasse 10 66123 Saarbrücken Germany; Centre de Recherche sur les Macromolécules Végétales (CERMAV-UPR5301); CNRS and Université Grenoble Alpes, BP53; 38041 Grenoble cedex 9 France; Chemical Biology of Carbohydrates; Helmholtz Institute for Pharmaceutical Research Saarland (HIPS); Universitätsstrasse 10 66123 Saarbrücken Germany; Centre de Recherche sur les Macromolécules Végétales (CERMAV-UPR5301); CNRS and Université Grenoble Alpes, BP53; 38041 Grenoble cedex 9 France; Department of Chemistry and Graduate School Chemical Biology; University of Konstanz; 78457 Konstanz Germany; Department of Chemistry and Graduate School Chemical Biology; University of Konstanz; 78457 Konstanz Germany; Centre de Recherche sur les Macromolécules Végétales (CERMAV-UPR5301); CNRS and Université Grenoble Alpes, BP53; 38041 Grenoble cedex 9 France; Chemical Biology of Carbohydrates; Helmholtz Institute for Pharmaceutical Research Saarland (HIPS); Universitätsstrasse 10 66123 Saarbrücken Germany (2015-12)
  • Synthesis of mannoheptose derivatives and their evaluation as inhibitors of the lectin LecB from the opportunistic pathogen Pseudomonas aeruginosa.

    Hofmann, Anna; Sommer, Roman; Hauck, Dirk; Stifel, Julia; Göttker-Schnetmann, Inigo; Titz, Alexander; hemical Biology of Carbohydrates, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), D-66123 Saarbrücken, Germany. (2015-05-05)
    Biofilm formation and chronic infections with Pseudomonas aeruginosa depend on lectins produced by the bacterium. The bacterial C-type lectin LecB binds to the two monosaccharides l-fucose and d-mannose and conjugates thereof. Previously, d-mannose derivatives with amide and sulfonamide substituents at C6 were reported as potent inhibitors of the bacterial lectin LecB and LecB-mediated bacterial surface adhesion. Because d-mannose establishes a hydrogen bond via its 6-OH group with Ser23 of LecB in the crystal structure and may be beneficial for binding affinity, we extended d-mannose and synthesized mannoheptoses bearing the free 6-OH group as well as amido and sulfonamido-substituents at C7. Two series of diastereomeric mannoheptoses were synthesized and the stereochemistry was determined by X-ray crystallography. The potency of the mannoheptoses as LecB inhibitors was assessed in a competitive binding assay. The data reveal a diastereoselectivity of LecB for (6S)-mannoheptose derivatives with increased activity over methyl α-d-mannoside.
  • Mimetics of Sialyl Lewis<SUP>x</SUP>: The Pre-Organization of the Carboxylic Acid is Essential for Binding to Selectins

    Titz, Alexander; Ernst, Beat; Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Campus C 2.3, D-66123, Saarbrücken, Germany (2014-12-05)
  • New approaches to control infections: anti-biofilm strategies against gram-negative bacteria.

    Sommer, Roman; Joachim, Ines; Wagner, Stefanie; Titz, Alexander; University of Konstanz, Department of Chemistry and Zukunftskolleg, Universitätsstrasse 10, D-78457 Konstanz. (2013)
    Hospital-acquired bacterial infections, especially with Gram-negative pathogens, present a major threat due to the rapid spread of antibiotic-resistant strains. Targeting mechanisms of bacterial virulence has recently appeared as a promising new therapeutic paradigm. Biofilm formation is a bacterial lifestyle, which offers a survival advantage through its protective matrix against host immune defense and antibiotic treatment. Interfering with biogenesis of adhesive organelles, bacterial communication or carbohydrate-mediated adhesion as anti-biofilm strategies are reviewed.
  • A Biophysical Study with Carbohydrate Derivatives Explains the Molecular Basis of Monosaccharide Selectivity of the Pseudomonas aeruginosa Lectin LecB.

    Sommer, Roman; Exner, Thomas E; Titz, Alexander; Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Campus C 2.3, D-66123, Saarbrücken, Germany; Department of Chemistry and Graduate School Chemical Biology, University of Konstanz, D-78457, Konstanz, Germany. (2014)
    The rise of resistances against antibiotics in bacteria is a major threat for public health and demands the development of novel antibacterial therapies. Infections with Pseudomonas aeruginosa are a severe problem for hospitalized patients and for patients suffering from cystic fibrosis. These bacteria can form biofilms and thereby increase their resistance towards antibiotics. The bacterial lectin LecB was shown to be necessary for biofilm formation and the inhibition with its carbohydrate ligands resulted in reduced amounts of biofilm. The natural ligands for LecB are glycosides of d-mannose and l-fucose, the latter displaying an unusual strong affinity. Interestingly, although mannosides are much weaker ligands for LecB, they do form an additional hydrogen bond with the protein in the crystal structure. To analyze the individual contributions of the methyl group in fucosides and the hydroxymethyl group in mannosides to the binding, we designed and synthesized derivatives of these saccharides. We report glycomimetic inhibitors that dissect the individual interactions of their saccharide precursors with LecB and give insight into the biophysics of binding by LecB. Furthermore, theoretical calculations supported by experimental thermodynamic data suggest a perturbed hydrogen bonding network for mannose derivatives as molecular basis for the selectivity of LecB for fucosides. Knowledge gained on the mode of interaction of LecB with its ligands at ambient conditions will be useful for future drug design.
  • Caenorhabditis elegans N-glycan core beta-galactoside confers sensitivity towards nematotoxic fungal galectin CGL2.

    Butschi, Alex; Titz, Alexander; Wälti, Martin A; Olieric, Vincent; Paschinger, Katharina; Nöbauer, Katharina; Guo, Xiaoqiang; Seeberger, Peter H; Wilson, Iain B H; Aebi, Markus; Hengartner, Michael O; Künzler, Markus; Institute of Molecular Biology, University of Zürich, Zürich, Switzerland. (2010-01)
    The physiological role of fungal galectins has remained elusive. Here, we show that feeding of a mushroom galectin, Coprinopsis cinerea CGL2, to Caenorhabditis elegans inhibited development and reproduction and ultimately resulted in killing of this nematode. The lack of toxicity of a carbohydrate-binding defective CGL2 variant and the resistance of a C. elegans mutant defective in GDP-fucose biosynthesis suggested that CGL2-mediated nematotoxicity depends on the interaction between the galectin and a fucose-containing glycoconjugate. A screen for CGL2-resistant worm mutants identified this glycoconjugate as a Galbeta1,4Fucalpha1,6 modification of C. elegans N-glycan cores. Analysis of N-glycan structures in wild type and CGL2-resistant nematodes confirmed this finding and allowed the identification of a novel putative glycosyltransferase required for the biosynthesis of this glycoepitope. The X-ray crystal structure of a complex between CGL2 and the Galbeta1,4Fucalpha1,6GlcNAc trisaccharide at 1.5 A resolution revealed the biophysical basis for this interaction. Our results suggest that fungal galectins play a role in the defense of fungi against predators by binding to specific glycoconjugates of these organisms.
  • Methylated glycans as conserved targets of animal and fungal innate defense.

    Wohlschlager, Therese; Butschi, Alex; Grassi, Paola; Sutov, Grigorij; Gauss, Robert; Hauck, Dirk; Schmieder, Stefanie S; Knobel, Martin; Titz, Alexander; Dell, Anne; Haslam, Stuart M; Hengartner, Michael O; Aebi, Markus; Künzler, Markus (2014-07-08)
    Effector proteins of innate immune systems recognize specific non-self epitopes. Tectonins are a family of β-propeller lectins conserved from bacteria to mammals that have been shown to bind bacterial lipopolysaccharide (LPS). We present experimental evidence that two Tectonins of fungal and animal origin have a specificity for O-methylated glycans. We show that Tectonin 2 of the mushroom Laccaria bicolor (Lb-Tec2) agglutinates Gram-negative bacteria and exerts toxicity toward the model nematode Caenorhabditis elegans, suggesting a role in fungal defense against bacteria and nematodes. Biochemical and genetic analysis of these interactions revealed that both bacterial agglutination and nematotoxicity of Lb-Tec2 depend on the recognition of methylated glycans, namely O-methylated mannose and fucose residues, as part of bacterial LPS and nematode cell-surface glycans. In addition, a C. elegans gene, termed samt-1, coding for a candidate membrane transport protein for the presumptive donor substrate of glycan methylation, S-adenosyl-methionine, from the cytoplasm to the Golgi was identified. Intriguingly, limulus lectin L6, a structurally related antibacterial protein of the Japanese horseshoe crab Tachypleus tridentatus, showed properties identical to the mushroom lectin. These results suggest that O-methylated glycans constitute a conserved target of the fungal and animal innate immune system. The broad phylogenetic distribution of O-methylated glycans increases the spectrum of potential antagonists recognized by Tectonins, rendering this conserved protein family a universal defense armor.