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Biomedical subjects

Peter H Seeberger

Publications and source records attributed to Peter H Seeberger.

At least 19 recordsLinked to original sources
PubMed2007

Probing glycomics.

The study of protein-carbohydrate interactions is one central theme of glycomics research. The challenges encountered when investigating these interactions have resulted in an approach that studies saccharides through the enzymes that process them. Proteins and their function are often probed by manipulating the genes that encode them. Efforts in proteoglycomics exploring protein-binding properties and the enzymatic modification of carbohydrates have intensified, and synthetic tools, including activity- and affinity-based probes, have enhanced our understanding of the roles of carbohydrates in biology.

Carbohydrate Conformation↗
PubMed2006

Multiple modes of binding enhance the affinity of DC-SIGN for high mannose N-linked glycans found on viral glycoproteins.

The dendritic cell surface receptor DC-SIGN and the closely related endothelial cell receptor DC-SIGNR specifically recognize high mannose N-linked carbohydrates on viral pathogens. Previous studies have shown that these receptors bind the outer trimannose branch Manalpha1-3[Manalpha1-6]Manalpha present in high mannose structures. Although the trimannoside binds to DC-SIGN or DC-SIGNR more strongly than mannose, additional affinity enhancements are observed in the presence of one or more Manalpha1-2Manalpha moieties on the nonreducing termini of oligomannose structures. The molecular basis of this enhancement has been investigated by determining crystal structures of DC-SIGN bound to a synthetic six-mannose fragment of a high mannose N-linked oligosaccharide, Manalpha1-2Manalpha1-3[Manalpha1-2Manalpha1-6]Manalpha1-6Man and to the disaccharide Manalpha1-2Man. The structures reveal mixtures of two binding modes in each case. Each mode features typical C-type lectin binding at the principal Ca2+-binding site by one mannose residue. In addition, other sugar residues form contacts unique to each binding mode. These results suggest that the affinity enhancement displayed toward oligosaccharides decorated with the Manalpha1-2Manalpha structure is due in part to multiple binding modes at the primary Ca2+ site, which provide both additional contacts and a statistical (entropic) enhancement of binding.

Carbohydrate Conformation↗
PubMed2006

Preparation and use of microarrays containing synthetic heparin oligosaccharides for the rapid analysis of heparin-protein interactions.

Heparin is a highly sulfated, linear polymer that participates in a plethora of biological processes by interaction with many proteins. The chemical complexity and heterogeneity of this polysaccharide can explain the fact that, despite its widespread medical use as an anticoagulant drug, the structure-function relationship of defined heparin sequences is still poorly understood. Here, we present the chemical synthesis of a library containing heparin oligosaccharides ranging from di- to hexamers of different sequences and sulfation patterns. An amine-terminated linker was placed at the reducing end of the synthetic structures to allow for immobilization onto N-hydroxysuccinimide activated glass slides and creation of heparin microarrays. Key features of this modular synthesis, such as the influence of the amine linker on the glycosidation efficiency, the use of 2-azidoglucose as glycosylating agents for oligosaccharide assembly, and the compatibility of the protecting group strategy with the sulfation-deprotection steps, are discussed. Heparin microarrays containing this oligosaccharide library were constructed using a robotic printer and employed to characterize the carbohydrate binding affinities of three heparin-binding growth factors. FGF-1, FGF-2 and FGF-4 that are implicated in angiogenesis, cell growth and differentiation were studied. These heparin chips aided in the discovery of novel, sulfated sequences that bind FGF, and in the determination of the structural requirements needed for recognition by using picomoles of protein on a single slide. The results presented here highlight the potential of combining oligosaccharide synthesis and carbohydrate microarray technology to establish a structure-activity relationship in biological processes.

Angiogenesis Modulating Agents↗
PubMed2006

Microreactors as tools for synthetic chemists-the chemists' round-bottomed flask of the 21st century?

Will microreactors replace the round-bottomed flask to perform chemical reactions in the near future? Recent developments in the construction of microstructured reaction devices and their wide-ranging applications in many different areas of chemistry suggest that they can have a significant impact on the way chemists conduct their experiments. Miniaturizing reactions offers many advantages for the synthetic organic chemist: high-throughput scanning of reaction conditions, precise control of reaction variables, the use of small quantities of reagents, increased safety parameters, and ready scale-up of synthetic procedures. A wide range of single- and multiphase reactions have now been performed in microfluidic-based devices. Certainly, microreactors cannot be applied to all chemistries yet and microfluidic systems also have disadvantages. Limited reaction-time range, high sensitivity to precipitating products, and new physical, chemical, and analytical challenges have to be overcome. This concept article presents an overview of microfluidic devices available for chemical synthesis and evaluates the potential of microreactor technology in organic synthesis.

Journal Article↗
PubMed2006

Synthesis of a core arabinomannan oligosaccharide of Mycobacterium tuberculosis.

The synthesis of a core arabinomannan (AM) oligosaccharide from Mycobacterium tuberculosis has been achieved using a convergent [6 + 6] glycosylation strategy and a defined set of building blocks. Dodecasaccharide 1, containing the key AM structural features of lipoarabinomannan (LAM), was obtained in excellent yield and selectivity from hexamannan 3 and hexaarabinan 5. This flexible synthetic strategy involves late-stage couplings and modifications, thus providing ready access to several different LAM fragments. The incorporation of a thiol linker at the reducing end of the oligosaccharide allows for the attachment of these compounds to microarrays and protein carriers.

Mycobacterium tuberculosis↗
PubMed2006

De novo synthesis of aceric acid and an aceric acid building block.

The de novo synthesis of an aceric acid thioglycoside building block and the total synthesis of the plant carbohydrate aceric acid are described via a highly convergent strategy. Aldol reaction of acetaldehyde and a protected tartaric acid derivative provided the open chain carbohydrate. Subsequent acid treatment yielded the aceric acid thioglycoside in 35% total yield over five steps. Oxidative cleavage of the thioketal in the open chain carbohydrate and basic hydrolysis of the methyl ester furnished fully deprotected aceric acid in 31% yield over six steps.

Plants↗
PubMed2006

Expression cloning of cholesterol alpha-glucosyltransferase, a unique enzyme that can be inhibited by natural antibiotic gastric mucin O-glycans, from Helicobacter pylori.

Helicobacter pylori infects over half the world's population, but only 3% of those infected develop peptic ulcer, gastric cancer, and mucosa-associated lymphoid tissue (MALT) lymphoma. In H. pylori, alpha-glucosyl cholesterol constitutes more than 25% of cell wall lipids, and it has been suggested that alpha-glucosyl cholesterol is essential for H. pylori viability. Here, we identified cholesterol alpha-glucosyltransferase (CHLalphaGcT) using an expression cloning strategy and showed that this enzyme is distinctively inhibited by mucin-type O-glycans similar to those present in deeper portions of the gastric mucosa. Moreover, inactivation of CHLalphaGcT by homologous recombination led to H. pylori lethality. These results indicate that H. pylori CHLalphaGcT is a unique enzyme targeted by a natural antibiotic mucin and constitutes an excellent therapeutic target to prevent H. pylori-induced peptic ulcer, gastric carcinoma, and MALT lymphoma.

Amino Acid Sequence↗
PubMed2006

The affinity of the FimH fimbrial adhesin is receptor-driven and quasi-independent of Escherichia coli pathotypes.

Type-1 fimbriae are important virulence factors for the establishment of Escherichia coli urinary tract infections. Bacterial adhesion to the high-mannosylated uroplakin Ia glycoprotein receptors of bladder epithelium is mediated by the FimH adhesin. Previous studies have attributed differences in mannose-sensitive adhesion phenotypes between faecal and uropathogenic E. coli to sequence variation in the FimH receptor-binding domain. We find that FimH variants from uropathogenic, faecal and enterohaemorrhagic isolates express the same specificities and affinities for high-mannose structures. The only exceptions are FimHs from O157 strains that carry a mutation (Asn135Lys) in the mannose-binding pocket that abolishes all binding. A high-mannose microarray shows that all substructures are bound by FimH and that the largest oligomannose is not necessarily the best binder. Affinity measurements demonstrate a strong preference towards oligomannosides exposing Manalpha1-3Man at their non-reducing end. Binding is further enhanced by the beta1-4-linkage to GlcNAc, where binding is 100-fold better than that of alpha-d-mannose. Manalpha1-3Manbeta1-4GlcNAc, a major oligosaccharide present in the urine of alpha-mannosidosis patients, thus constitutes a well-defined FimH epitope. Differences in affinities for high-mannose structures are at least 10-fold larger than differences in numbers of adherent bacteria between faecal and uropathogenic strains. Our results imply that the carbohydrate expression profile of targeted host tissues and of natural inhibitors in urine, such as Tamm-Horsfall protein, are stronger determinants of adhesion than FimH variation.

Adhesins, Escherichia coli↗
PubMed2006

Merging organic and polymer chemistries to create glycomaterials for glycomics applications.

[Image: see text] Oligosaccharides at cell surfaces are known to play a critical role in many biological processes such as biorecognition, interactions between cells and with artificial surfaces, immune response, infection and inflammation. In order to facilitate studies of the role of sugars, an increasing number of novel tools are becoming available. New synthetic strategies now provide much more efficient access to complex carbohydrates or glycoconjugates. Branched carbohydrates and hybrids of carbohydrates conjugated to polymers have been prepared using solution and/or solid-phase synthesis and advanced methods of polymerization. These materials are essential for the development of methodologies to study and map the molecular structure-function relationship at interfaces. This article highlights recent advances in the synthesis of carbohydrates and polymer hybrids mimicking the properties and functionalities of the natural oligosaccharides, as well as selected applications in biology, biotechnology and diagnostics.

Carbohydrate Conformation↗
PubMed2006

Synthesis of glycosyl phosphates from 1,2-orthoesters and application to in situ glycosylation reactions.

[reaction: see text] A series of glycosyl phosphates were prepared in high yield by treatment of the corresponding 1,2-orthoesters with dibutyl phosphate. Glycosyl phosphates are efficient glycosylating agents even when used in crude form or when generated in situ. The immunodominant epitope trirhamnoside of group B Streptococcus was prepared to demonstrate the synthetic utility of the method.

Epitopes↗
PubMed2006

Enhancement of the immunogenicity of synthetic carbohydrates by conjugation to virosomes: a leishmaniasis vaccine candidate.

Novel virosomal formulations of a synthetic oligosaccharide were prepared and evaluated as vaccine candidates against leishmaniasis. A lipophosphoglycan-related synthetic tetrasaccharide antigen was conjugated to a phospholipid and to the influenza virus coat protein hemagglutinin. These glycan conjugates were embedded into the lipid membrane of reconstituted influenza virus virosomes. The virosomal formulations elicited both IgM and IgG anti-glycan antibodies in mice, indicating an antibody isotype class switch to IgG. The antisera cross-reacted in vitro with the corresponding natural carbohydrate antigens expressed by leishmania cells. These findings support the concept of using virosomes as universal antigen delivery platform for synthetic carbohydrate vaccines.

Carbohydrates↗
PubMed2006

Total synthesis of phosphatidylinositol mannosides of Mycobacterium tuberculosis.

The total synthesis of phosphatidylinositol mannosides (PIMs), a key class of antigenic glycolipids found on the cell wall of Mycobacterium tuberculosis, is described. The synthetic strategy relied on a [4 + 3] glycosylation of tetramannoside 1 and pseudotrisaccharide 2, which allowed for convergent access to the glycan backbone of the phosphatidylinositol dimannoside (PIM2) and hexamannoside (PIM6). A short practical synthesis of tuberculostearic acid was achieved based on a copper-catalyzed cross-coupling reaction. Union of the glycan and lipid parts resulted in the first total synthesis of native PIM2 and PIM6.

Carbohydrate Sequence↗
PubMed2006

Microarrays of synthetic heparin oligosaccharides.

We present the first preparation of microarrays containing synthetic heparin oligosaccharides in order to elucidate the heparin-protein interactions involved in a variety of biological processes. For this purpose, we have developed a novel linker strategy that is compatible with the protecting-group manipulations required for the synthesis of the highly sulfated oligosaccharides and can also be extended to an automated solid phase approach. Strategic placement of the orthogonally protected amine linker was key to the success of the array construction. These heparin chips allow for the high-throughput screening of oligosaccharides by using approximately picomoles of protein. The potential of the new method was demonstrated by probing the carbohydrate affinity of two heparin-binding growth factors, FGF-1 and FGF-2, that are implicated in the development and differentiation of several tumors.

Carbohydrate Sequence↗
PubMed2006

Oligosaccharide microarrays to map interactions of carbohydrates in biological systems.

Carbohydrate microarrays are becoming a standard tool for glycobiologists to screen large numbers of sugars and elucidate the role of carbohydrates in biological systems. This article describes detailed methods to prepare and use microarrays containing synthetic oligosaccharides as well as a summary of the biological information that can be obtained by using this technology. These methods use different linking chemistries to immobilize a wide range of synthetic oligosaccharides onto glass slides through the formation of a covalent bond. Therefore, this technology enables the elaborate study of a great variety of carbohydrate interactions.

Aminoglycosides↗