Synthetic Assembly of Bifluorescence-Labeled Glycopolymers as Substrates for Assaying α-Amylase by Resonance Energy Transfer

Interpenetrating Polymer Network Capturing FRET-Sensitive Polymers Available for an Enzyme Assay

Fluorogenic glycomonomers have been used for biological evaluations, and water-soluble and Förster resonance energy transfer (FRET)-sensitive glycopolymers have also been reported. A FRET-sensitive polymer was conveniently prepared from a fluorogenic donor monomer and a fluorogenic acceptor monomer by means of simple radical polymerization in high yield. Continuous fluorospectroscopic monitoring of the polymer in the presence of an enzyme was performed, and the results showed the possible application of the FRET-sensitive glycopolymer for practical use. In addition to the use of aqueous solution phase, the water-soluble and FRET-sensitive glycopolymer was completely captured into an interpenetrating polymer network (IPN) by means of radical polymerization with a combination of acrylamide and bis-acrylamide as used for the cross-linking reagent system. The IPN including the FRET-sensitive glycopolymer was allowed to react with amylases in an aqueous buffer solution at 37 °C, and the enzymatic reaction was continuously and conveniently monitored by means of fluorometric spectroscopy.

Fluorogenic glycopolymers available for determining the affinity of lectins by intermolecular FRET

A convenient assembly of fluorogenic glycopolymers having various polymer compositions was accomplished from the corresponding glycomonomer and dansyl monomer by means of radical polymerization, and the water-soluble glycopolymers gave typical fluorescence spectroscopic profiles due to the dansyl moieties on the glycopolymer in aqueous media. Biological evaluation of the polymer against wheat germ agglutinin (WGA) was accomplished on the basis of fluorescence changes due to tryptophan residues on WGA, and the affinities between the glycopolymers and WGA were estimated to be 4.7 × 10⁵ to 9.3 × 10⁵ M^-1. In order to apply the fluorogenic glycopolymers for further biological measurements, efficient resonance energy transfer from tryptophan moieties on WGA to dansyl moieties on the fluorogenic glycopolymers was examined. FRET profiles of both fluorophores were similar compared to the binding profiles on the basis of fluorescence changes of tryptophan residues. This approach is applicable for the determination of an affinity constant between a carbohydrate and a lectin in which no fluorophore exists near the binding site.

Preparation of Functional Monomers as Precursors of Bioprobes from a Common Styrene Derivative and Polymer Synthesis

CM-Str (4-(Chloromethyl)styrene) was used as a useful starting material for the construction of a series of functional monomers. Substitution of the chlorine to the corresponding azide was performed, and the reduction of the azide proceeded smoothly to afford an aminostyrene, which was used as a common precursor for the preparation of functional monomers. Condensation of the amine with a fluorophore, biotin and carbohydrate was accomplished. Among the monomers, a carbohydrate monomer was polymerized with or without acrylamide as a model polymerization to yield the corresponding water-soluble glycopolymers, and biological evaluations of the glycopolymers for a lectin, and wheat germ agglutinin (WGA), were carried out on the basis of the fluorescence change of tryptophan in the WGA.

Synthetic construction of sugar-amino acid hybrid polymers involving globotriaose or lactose and evaluation of their biological activities against Shiga toxins produced by Escherichia coli O157:H7

Synthetic assembly of sugar moieties and amino acids in order to create "sugar-amino acid hybrid polymers" was accomplished by means of simple radical polymerization of carbohydrate monomers having an amino acid-modified polymerizable aglycon. Amines derived from globotriaoside and lactoside as glycoepitopes were condensed with known carbobenzyloxy derivatives, including Z-Gly, Z-l-Ala and Z-β-Ala, which had appropriate spacer ability and a chiral center to afford fully protected sugar-amino acid hybrid compounds in good yields. After deprotection followed by acryloylation, the water-soluble glycomonomers were polymerized with or without acrylamide in the presence of a radical initiator in water to give corresponding copolymers and homopolymers, which were shown by SEC analysis to have high molecular weights. Evaluation of the biological activities of the glycopolymers against Shiga toxins (Stxs) was carried out, and the results suggested that glycopolymers having highly clustered globotriaosyl residues had high affinity against Stx2 (K_D = 2.7∼4.0 µM) even though other glycopolymers did not show any affinity or showed very weak binding affinity. When Stx1 was used for the same assay, all of the glycopolymers having globotriaosyl residues showed high affinity (K_D = 0.30∼1.74 µM). Interestingly, couple of glycopolymers having lactosyl moieties had weaker binding affinity against Stx1. In addition, when cytotoxicity assays were carried out for both Stxs, glycopolymers having highly clustered globotriaosyl residues showed higher affinity than that of the copolymers, and only highly clustered-type glycopolymers displayed neutralization potency against Stx2.

Synthetic Assembly of Mannose Moieties Using Polymer Chemistry and the Biological Evaluation of Its Interaction towards Concanavalin A

Protein-carbohydrate interactions exhibit myriad intracellular recognition events, so understanding and investigating their specific interaction with high selectivity and strength are of crucial importance. In order to examine the effect of multivalent binding on the specificity of protein-carbohydrate interactions, we synthesized mannose glycosides as a novel type of glycosylated monomer and glycopolymers of polyacrylamide derivatives with α-mannose (α-Man) by radical polymerization and monitored their strength of interaction with concanavalin A (Con A) by surface plasmon resonance (SPR) detection. In a quantitative test using the Con A-immobilized sensor surface, the kinetic affinity for the synthesized polymers, 8a (KD = 3.3 × 10-6 M) and 8b (KD = 5.3 × 10-5 M), were concentration-dependent, showing strong, specific molecular recognition abilities with lectin. Our study showed the enhancement in recognition specificity for multivalent saccharides, which is often mediated by cell surface carbohydrate-binding proteins that exhibit weak affinity and broad specificity for the individual ligands.

Fluorescence chemosensors for hydrogen sulfide detection in biological systems

A comprehensive review of the development of H2S fluorescence-sensing strategies, including sensors based on chemical reactions and fluorescence resonance energy transfer (FRET), is presented. The advantages and disadvantages of fluorescence-sensing strategies are compared with those of traditional methods. Fluorescence chemosensors, especially those used in FRET sensing, are highly promising because of their low cost, technical simplicity, and their use in real-time sulfide imaging in living cells. Potential applications based on sulfate reduction to H2S, the relationship between sulfate-reducing bacteria activity and H2S yield, and real-time detection of sulfate-reducing bacteria activity using fluorescence sensors are described. The current challenges, such as low sensitivity and poor stability, are discussed.

Fluorescence of N-acylated dansylamide with a long hydrophobic tail: sensitive response to premicellar aggregation of sodium deoxycholate

The present work describes the synthesis and photophysical studies of two fluorescent dansylamide derivatives, in which the amine group is acylated by a long hydrophobic chain (a part of a biologically relevant palmitic acid) and by a short hydrophobic tail (a part of acetic acid).