Synthesis of poly(N-acetyl-beta-lactosaminide-carrying acrylamide): chemical-enzymatic hybrid process

Detection of carbohydrate-binding proteins by oligosaccharide-modified polypyrrole interfaces using electrochemical surface plasmon resonance

This paper reports on the use of electrochemical surface plasmon resonance (E-SPR) for the detection of carbohydrate-binding proteins. The generation of an SPR sensor specific to lectins Arachis hypogaea (PNA) and Maackia amurensis (MAA) is based on the electrochemical polymerization of oligosaccharide derivatives functionalized by pyrrole groups. The resulting thin conducting polymer films were characterized using E-SPR and atomic force microscopy (AFM). The specific binding of PNA to polypyrrole-lactosyl and of MAA to polypyrrole-3'-sialyllactosyl films was investigated using SPR. The detection limit was 41 nM for PNA and 83 nM for MAA. Through Scatchard analysis and linear transformation of the SPR sensorgram data, association (k(ass)) and dissociation rate constants (k(diss)) could be determined.

Development and application of diazirines in biological and synthetic macromolecular systems

Many different reagents and methodologies have been utilised for the modification of synthetic and biological macromolecular systems. In addition, an area of intense research at present is the construction of hybrid biosynthetic polymers, comprised of biologically active species immobilised or complexed with synthetic polymers. One of the most useful and widely applicable techniques available for functionalisation of macromolecular systems involves indiscriminate carbene insertion processes. The highly reactive and non-specific nature of carbenes has enabled a multitude of macromolecular structures to be functionalised without the need for specialised reagents or additives. The use of diazirines as stable carbene precursors has increased dramatically over the past twenty years and these reagents are fast becoming the most popular photophors for photoaffinity labelling and biological applications in which covalent modification of macromolecular structures is the basis to understanding structure-activity relationships. This review reports the synthesis and application of a diverse range of diazirines in macromolecular systems.

Design, functional evaluation and biomedical applications of carbohydrate dendrimers (glycodendrimers)

Receptors for carbohydrates of the lectin type are multisubunit and multivalent proteins with many important biological functions. In order to put their unique biological activities into use in biotechnology and biomedicine, efficient carbohydrate ligands of the glycodendrimer type have been constructed. Although these compounds may be branched into the multiple generations, structures bearing four to 16 terminal carbohydrate substituents have proved to be efficient ligands in most lectin systems. These compounds are rapidly finding important practical applications as antitumor and antiinfective compounds.

Analysis of specific interactions of synthetic glycopolypeptides carrying N-acetyllactosamine and related compounds with lectins

Analysis of interactions of synthetic glycopolypeptides with lectins was performed with a biosensor based on surface plasmon resonance (SPR). A series of synthetic oligosaccharide-substituted poly(L-glutamic acid)s were immobilized on sensor surfaces via the gamma-carboxyl groups of their peptide moieties by the surface thiol coupling method. Artificial glycopolypeptides: an N-acetyllactosamine-substituted polymer (1), an N-acetylisolactosamine-substituted polymer (2), a (GlcNAc)3-substituted polymer (3), a (GlcNAc)2-substituted polymer (4), and a p-aminophenyl N-acetyl-beta-lactosaminide-substituted polymer (5), were used as the ligands. On analysis by SPR, surface-bound polymers 1 and 5 reacted with Erythrina cristagalli agglutinin (ECA), Lycopersicon esculentum agglutinin (LEA), Ricinus communis agglutinin-120 (RCA120), and wheat germ (Triticum vulgaris) agglutinin (WGA). Polymer 2 reacted with WGA and RCA120, but did not with ECA and LEA. The results indicate that beta-(1-->4)-linked galactosyl residues are needed for binding to ECA and LEA. Polymer 3 reacted strongly with LEA and WGA, but polymer 4 reacted strongly only with WGA. Affinity constants (KA) for surface-bound polymer 5-lectin interactions were also about 4-61 times as strong as those for surface-bound polymer 1-lectin interactions. These artificial glycopolypeptides were shown to be useful as tools and probes of carbohydrate recognition and modeling in the analysis of glycoprotein-lectin interactions.

Enzymatic synthesis of beta-D-Gal-(1 --> 3)-[beta-D-GlcNAc-1 --> 6)]-alpha-D-GalNAc-OC6H4NO2-p as a carbohydrate unit of mucin-type 2 core

We have established a synthetic method for obtaining beta-D-Gal-(1 --> 3)-beta-D-GlcNAc-(1 --> 6)]-alpha-D-GalNAc-OC6H4NO2-p (1), which is a carbohydrate unit of mucin-type 2 core. A beta-N-acetyl-D-hexosaminidase from Nocardia orientalis catalyzed the synthesis of the desired compound 1 with its isomers beta-D-GalNAc-(1 --> 6)-beta-D-Gal-(1 --> 3)-alpha-D-GalNAc-OC6H4NO2-p (2) beta-D-GlcNAc-(1 --> 3)-beta-D-Glc-(1 --> 3)-alpha-D-GalNAc-OC6H4NO2-p (3) through N-acetylglucosaminyl transfer from N,N'-diacetylchitobiose and beta-D-Gal-(1 --> 3)-alpha-D-GalNAc-OC6H4NO2-p. The enzyme formed the trisaccharides 1, 2, and 3 in 14% overall yield based on beta-D-Gal-(1 --> 3)-alpha-D-GalNAc-OC6H4NO2-p as an acceptor substrate, and in the ratio of 44:32:24. In this way, N-acetylglucosaminyl transfer favored O-6 of the acceptor rather than O-6', and occurred to a lesser extent at O-3'. This reaction was efficient enough to allow a one-pot preparation of the desired carbohydrate unit of mucin-type 2 core. When beta-D-Gal-(1 --> 3)-beta-D-GalNAc-OC6H4NO2-p was used as an acceptor, the enzyme also synthesized three kinds of trisaccharides in the same regioselectivity with respect to O-6 and O-6' versus O-3' of the acceptor.

Development of an enzyme-linked immunosorbent assay-based method for measuring galactosyltransferase activity using a synthetic glycopolymer acceptor substrate

A lectin-assisted enzyme-linked immunosorbent assay (ELISA)-based method using a synthetic glycopolymer as an acceptor substrate was developed for measuring beta 1,4-galactosyltransferase (GalT) activity. A polyacrylamide derivative having a beta-linked N-acetylglucosamine (GlcNAc beta) moiety on each monomeric unit was synthesized chemically and immobilized on a polystyrene microtiter plate as an acceptor substrate for GalT. After the plate was incubated with bovine GalT, the enzyme reaction product, beta-linked Gal residue on the polyacrylamide-bound GlcNAc residue, was detected by using Ricinus communis agglutinin 1 (RCA1), rabbit anti-RCA1 antibody, and a peroxidase-labeled anti-rabbit IgG. The lowest GalT concentration detectable by this method was about 0.5 mU/ml, which is comparable to those by the previously reported ELISA-based assays. The unique property of the glycopolymer, PAP(GlcNAc beta), of binding noncovalently but tightly to the polystyrene microtiter plate allowed the use of this acceptor substrate for the GalT activity measurement even in the presence of 1% Triton CF-54 and X-100. Our system was successfully applied to assess GalT activity in milk of various mammals.

Preparation of oligosaccharide units library and its utilization

There is high current interest in developing synthetic routes to oligosaccharides involved in glycoconjugates. Significant attention has been focused on the application of glycosidase-catalyzed transglycosylation for practical synthesis of oligosaccharides. The enzymatic synthesis has become more practical by the use of several glycosidases available in sufficient quantities. This review describes convenient syntheses of di- and trisaccharide units, which are related to molecular recognition, by using regioselective transgalactosylation, trans-N-acetylglucosaminylation, transfucosylation, and transmannosylation. The regioselectivity could be controlled to some extent by using the following techniques: (1) varying enzymes, (2) organic co-solvent system, (3) the configuration of the existing glycosidic linkage of the acceptor and (4) inclusion complex of acceptor glycoside with cyclodextrin. Furthermore, glycopolymers carrying a series of disaccharides containing beta-D-galactosyl residues were synthesized and used as a model in oligosaccharide-lectin interaction analysis. These water-soluble glycopolymers were shown to be useful as probes of carbohydrate recognition.

Strength in numbers: non-natural polyvalent carbohydrate derivatives

Many processes mediated by protein-carbohydrate interactions involve multivalent low-affinity binding, which is inherently difficult to study. New structural templates for the generation of multivalent carbohydrate displays have recently been developed, and tailored multivalent saccharide derivatives can now be used to study and modulate a wide variety of biological recognition events.