Synthesis of polyanionic glycopolymers for the facile assembly of glycosyl arrays

Synthesis of a Novel Polyaniline Glycopolymer and its Lectin Binding Studies

We report the multistep synthesis and polymerisation of a novel aniline derivative with a pendant α-d-mannose substituent. The α-D-mannose functionality was successfully introduced before polymerisation via copper-catalysed azide alkyne click chemistry and the resulting monomer was polymerised using general oxidative polymerisation conditions, producing a water soluble mannosylated polyaniline. The polymer was characterised by several techniques and compared with standard polyaniline. The selective binding of the polymer to Concanavalin A (ConA) was successfully demonstrated by the precipitation of polymer–ConA aggregates. Potential applications of these novel polyaniline glycopolymers could include the development of electroactive biomaterials with the ability to bind mannose receptors, or as sensors for proteins or microbes.

Use of lactose against the deadly biological toxin ricin

Developing a technology for detecting and decontaminating biological toxins is needed. Ricin from Ricinus communis is a highly poisonous toxin; it was formerly used for an assassination in London and in postal attacks in the United States. Ricin is readily available from castor beans and could be used as a biological agent. We propose using glycotechnology against the illegal use of ricin. Lactose (a natural ligand of this toxin) was incorporated into polyacrylamide-based glycopolymers at variable sugar densities (18-100%) and evaluated with surface plasmon resonance (SPR) spectroscopy and the real agent, ricin. Glycopolymers (18-65% lactose densities) effectively interfered with the toxin-lactoside adhesion event (>99% efficiency within 20 min). This supported the notion of using the mammary sugar lactose against a deadly biological toxin.

A novel isotherm, modeling self-assembled monolayer adsorption and structural changes

Self-assembled monolayers (SAMs) have numerous applications, for example, engine wear inhibitors, surface profiling signal enhancement, nanostructure production, sensor production, and catalysis. The adsorbed SAM structure has a major impact on the properties of the outer monolayer surface which dictates the performance and viability of the SAM for individual applications. Substrate growth phases of SAMs have been extensively studied, and two structures have been identified. Initially, a lying down SAM structure is formed that evolves into a standing up structure. It is often critical to know how both structures form as a function of substrate immersion time to be able to design the properties of this structure. The formation of mercaptopropionic acid (MPA) SAMs on gold has been studied. Electrochemical impedance spectroscopy (EIS) was used to measure the adsorption isotherms at five temperatures in the range 4-40 degrees C. Infrared reflectance absorption spectroscopy (IRRAS) was also used, and the results show close agreement. A new monolayer adsorption isotherm is proposed which models SAM structure formation as a function of immersion time, representing all phases of SAM adsorption. This model represents a significant improvement on previous models based on Langmuir and Kisliuk adsorption isotherms that only model the fractional coverage of a surface with a SAM. The new model predicts the optimum immersion time taken for an MPA monolayer on gold to attain a surface saturated with MPA. It accounts for temperature effects on the rate of formation and the degree of monolayer disorder. It has potential for use in other SAM systems and may become the method of choice for modeling many instances of sequential substrate adsorption of two different structures, each of which exhibits different properties, as a function of immersion time.

[Highly sensitive detection technology for biological toxins applying sugar epitopes]

The Shiga toxin is a highly poisonous protein produced by enterohemorrhagic Escherichia coli O157. This bacterial toxin causes the hemolytic uremic syndrome. Another plant toxin from castor beans, ricin, is also highly toxic. The toxin was used for assassination in London. Recently, there were several cases of postal matter containing ricin. Both toxins are categorized as biological warfare agents by the Centers of Disease Control and Prevention. Conventional detection methods based on the antigen-antibody reaction, PCR and other cell-free assays have been proposed. However, those approaches have drawbacks in terms of sensitivity, analytical time, or stability of the detection reagents. Therefore, development of a facile and sensitive detection method is essential. Here we describe new detection methods applying carbohydrate epitopes as the toxin ligands, which is based on the fact that the toxins bind cell-surface oligosaccharides. Namely, the Shiga toxin has an affinity for globobiosyl (Gb(2)) disaccharide, and ricin binds the beta-D-galactose residue. For Shiga toxin detection, surface plasmon resonance (SPR) was applied. A polyanionic Gb(2)-glycopolymer was designed for this purpose, and it was used for the assembly of Gb(2)-chips using alternating layer-by-layer technology. The method allowed us to detect the toxin at a low concentration of LD(50). A synthetic carbohydrate ligand for ricin was designed and immobilized on the chips. SPR analysis with the chips allows us to detect ricin in a highly sensitive and facile manner (10 pg/ml, 5 min). Our present approaches provide a highly effective way to counter bioterrorism.

Glycoarrays--tools for determining protein-carbohydrate interactions and glycoenzyme specificity

Carbohydrate arrays (glycoarrays) have recently emerged as a high-throughput tool for studying carbohydrate-binding proteins and carbohydrate-processing enzymes. A number of sophisticated array platforms that allow for qualitative and quantitative analysis of carbohydrate binding and modification on the array surface have been developed, including analysis by fluorescence spectroscopy, mass spectrometry and surface plasmon resonance spectroscopy. These platforms, together with examples of biologically-relevant applications are reviewed in this Feature Article.

Substrate specificity of N-acetylhexosaminidase from Aspergillus oryzae to artificial glycosyl acceptors having various substituents at the reducing ends

The substrate specificity of N-acetylhexosaminidase (E.C. 3.2.1.51) from Aspergillus oryzae was examined using p-nitrophenyl 6-O-sulfo-N-acetyl-beta-D-glucosaminide (6-O-sulfo-GlcNAc-O-pNP) as the glycosyl donor and a series of beta-d-glucopyranosides and N-acetyl-beta-D-glucosaminides with variable aglycons at the anomeric positions as the acceptors. When beta-D-glucopyranosides with methyl (CH(3)), allyl (CH(2)CHCH(2)), and phenyl (C(6)H(5)) groups at the reducing end were used as the acceptors, this enzyme transferred the 6-O-sulfo-GlcNAc moiety in the donor to the location of O-4 in these glycosyl acceptors with a high regioselectivity, producing the corresponding 6-O-sulfo-N-acetylglucosaminyl beta-D-glucopyranosides. However, beta-D-glucopyranose lacking aglycon was a poor substrate for transglycosylation. This A. oryzae enzyme could also accept various N-acetyl-beta-D-glucosaminides carrying hydroxyl (OH), methyl (CH(3)), propyl (CH(2)CH(2)CH(3)), allyl (CH(2)CHCH(2)) and p-nitrophenyl (pNP; C(6)H(4)-NO(2)) groups at their aglycons, yielding 6-O-sulfo-N-acetylglucosaminyl-beta(1-->4)-disaccharide products.

Bioactive galactose-branched polyelectrolyte multilayers and microcapsules: self-assembly, characterization, and biospecific lectin adsorption

We describe the fabrication of multilayers and microcapsules with biologically designed targeting activity using chemoenzymatic synthesized carbohydrate-branched polyelectrolytes. A novel cationic d-galactose-branched copolymer [poly(vinyl galactose ester-co-methacryloxyethyl trimethylammonium chloride), PGEDMC] is alternated with poly(styrene sulfonate) (PSS) to form thin multifilms by the layer-by-layer (LbL) technique on such different solid surfaces as quartz slides, poly(ethylene terephthalate) (PET) films, silicon wafers, and polystyrene (PS) microparticles. The experimental protocols were first optimized on flat, smooth silica substrates using UV-vis, contact angle, and atomic force microscopy (AFM) measurements. The film properties of PGEDMC/PSS multilayers are modified by varying polyelectrolyte concentration, ionic strength, and counteranion types. Hollow capsules were formed after the removal of colloidal templates; transmission (TEM) and scanning (SEM) electron microscopy were used to verify the LbL process integrity. PGEDMC/PSS planar films and capsules carrying beta-galactose as recognition signals have specific recognition abilities with peanut agglutinin (PNA) lectin rather than concanavalin A (Con A) lectin observed by fluorescence spectroscopy.

Synthesis of globo- and isoglobotriosides bearing a cinnamoylphenyl tag as novel electrophilic thiol-specific carbohydrate reagents

The galactosyl donor, 4,6-di-O-acetyl-2,3-di-O-benzyl-D-galactopyranosyl trichloroacetimidate, was efficiently coupled with regioselectively benzylated lactoside acceptors under standard conditions to stereoselectively afford the corresponding globotrioside and isoglobotrioside derivatives in very good yields. These glycosides were smoothly functionalized with a 6-(p-cinnamoylphenoxy)-hexyl tether tag as novel electrophilic thiol-specific carbohydrate reagents. Immobilization of the globotrioside conjugate to Thiopropyl Sepharose 6B for purification of B-subunit of Shiga toxin (StxB) and coupling of a model cysteine-containing protein (StxB-Z(n)-Cys) to the isoglobotrioside conjugate were both performed with high efficiency.

Convenient enzymatic synthesis of a p-nitrophenyl oligosaccharide series of sialyl N-acetyllactosamine, sialyl Lex and relevant compounds

From the beta-D-Gal-(1-->4)-beta-D-GlcNAc-OC6H4NO2-p (1) prepared by the transglycosylation of beta-galactosidase from Bacillus circulans, alpha-D-Neu5Ac-(2-->3)-beta-D-Gal-(1-->4)-beta-D-GlcNAc-OC6H4NO2-p (9) and alpha-D-Neu5Ac-(2-->6)-beta-D-Gal-(1-->4)-beta-D-GlcNAc-OC6H4NO2-p (10) were effectively synthesized with an equimolar ratio of CMP-Neu5Ac by recombinant rat alpha-(2-->3)-N-sialyltransferase and rat liver alpha-(2-->6)-N-sialyltransferase, respectively. The former enzyme also transferred effectively the Neu5Ac residue from CMP-Neu5Ac to the location of OH-3 in the non-reducing terminal of beta-D-Gal-(1-->4)-beta-D-Gal-OC6H4NO2-p or beta-D-Gal-(1-->4)-beta-D-Gal-(1-->4)-beta-D-GlcNAc-OC6H4NO2-p, while the latter enzyme did not. In the case of equimolar ratio of GDP-Fuc/acceptor, 1 and 9 were further fucosylated quantitatively to form beta-D-Gal-(1-->4)-beta-D-(alpha-l-Fuc-(1-->3)-)-GlcNAc-OC6H4NO2-p (14) and alpha-D-Neu5Ac-(2-->3)-beta-D-Gal-(1-->4)-beta-D-(alpha-l-Fuc-(1-->3)-)-GlcNAc-OC6H4NO2-p (13) by recombinant human alpha-(1-->3)-fucosyltransferase VII, respectively.