Analysis of lectin properties with membrane ultrafiltration and high-pressure liquid chromatography

Centrifugal ultrafiltration-HPLC method for interaction analysis between lectins and sugars

The centrifugal ultrafiltration-HPLC method is a simple and rapid method for analyzing the binding interaction between lectins and sugars (oligosaccharides). In this method, a lectin is mixed with a fluorescent-labeled oligosaccharide in buffer and the unbound oligosaccharide recovered by centrifugal ultrafiltration is isolated and quantified by high-performance liquid chromatography. The binding activity is defined as a ratio (percentage) of the amount of bound oligosaccharide to that added, where the former is obtained by subtracting the amount of unbound oligosaccharide from the latter. The oligosaccharide-binding specificity of a lectin can be determined by comparing the binding activities with a variety of fluorescent-labeled oligosaccharides. The association constant and the optimum pH and temperature of the binding interaction between lectins and fluorescent-labeled oligosaccharides can be easily analyzed by this method.

Parallel quantification of lectin-glycan interaction using ultrafiltration

Using ultrafiltration membrane, a simple method for screening protein-ligand interaction was developed. The procedure comprises three steps: mixing ligand with protein, ultrafiltration of the solution, and quantification of unbound ligands by HPLC. By conducting analysis with variable protein concentrations, affinity constants were easily obtained. Multiple ligands can be analyzed simultaneously as a mixture, when concentration of ligands was controlled. Feasibility of this method for lectin-glycan interaction analysis was examined using fluorescently labeled high-mannose-type glycans and recombinant intracellular lectins or endo-α-mannosidase mutants. Estimated Ka values of malectin and VIP36 were in good agreement indeed with those evaluated by conventional methods such as isothermal titration calorimetry (ITC) or frontal affinity chromatography (FAC). Finally, several mutants of endo-α-mannosidase were produced and their affinities to monoglucosylated glycans were evaluated.

Functional and structural characterization of multiple galectins from the skin mucus of conger eel, Conger myriaster

The complete amino acid sequence of an isogalectin, named congerin II, isolated from the skin mucus of conger eel, was determined by sequencing of the protein and its peptides generated by enzymatic and chemical cleavages. Congerin II consisted of 135 amino acids residues containing an acetylated N-terminus. Congerin II was found to be only 46% homologous in sequence to congerin I which was previously determined (Muramoto K., Kamiya H., Biochem. Biophys. Acta, 1992;1116:129-136), suggesting that the galectins with diverse molecular properties are present in the skin mucus of conger eel. However, it was confirmed by analysis of the secondary structures using circular dichroism that both congerins I and II shared similar folds characterized by beta structures. Congerins I and II showed different molecular properties such as thermostability, pH dependency for hemagglutinating activity and for binding specificity against the pyridylamino derivative of lactose. Congerin I showed more strict recognition specificity for lactose than did congerin II. Furthermore, the effects of chemical modification on congerins I and II were investigated in order to identify the type of amino acids involved in their different lectin activities. Modification of tyrosine and lysine residues did not affect the carbohydrate-binding activities of congerins. However, modification of tryptophan, arginine, histidine, glutamic acid and aspartic acid residues led to considerable loss of their activities, and a different mode of binding activity was observed between modified congerins I and II. These results suggest that multiple galectins from conger eel with the same scaffold have different biological functions and properties.

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.

Determination of the interactions between lectins and glycoproteins by surface plasmon resonance

A simple and rapid analytical method for detecting interactions between oligosaccharides of glycoproteins and different lectins was studied by surface plasmon resonance using a biosensor (BIAcore). The interactions of three lectins, Sambucus sieboldiana agglutinin (SSA), Ricinus communis agglutinin I (RCA I) and Concanavalin A (Con A) for fetuin and digested fetuins with glycosidases, asialo-, agalacto-, and aglucosamino-fetuin, were investigated as a model system. These fetuins were immobilized to the matrix of of the sensor chip and the lectins were injected into the sensor chip cartridge. The association and dissociation reactions could be monitored as resonance signals in real time. The interactions with lectins significantly changed as the oligosaccharides of fetuin were trimmed. The interactions between fetuin and SSA, asialofetuin and RCA I, and aglucosaminofetuin and Con A show the highest affinity properties, respectively. The association constants of these lectins were estimated to be 1.4 x 10(7), 1.9 x 10(8) and 5.3 x 10(7) (M-1), respectively. These results suggested that the interactions between lectins and glycoproteins could be well defined in real time and kinetically, and that the partial structure of oligosaccharides of glycoproteins can be estimated by determination of the interactions with various lectins after glycosidase digestions using the biosensor.

Kinetic measurement of the interaction between an oligosaccharide and lectins by a biosensor based on surface plasmon resonance

Kinetic measurements of the interaction between an oligosaccharide and various lectins were performed using a biosensor based on surface plasmon resonance (SPR). A glycopeptide, prepared from asialofetuin and having a nearly homogeneous N-linked sugar chain, was immobilized on the surface of a sensor chip via the amino groups of its peptide moiety. The interactions of this bound glycopeptide with six lectins [Sambucus sieboldiana lectin, Maackia amurensis lectin, Aleuria aurantia lectin, Ricinus communis agglutinin-120 (RCA120), Datura stramonium lectin (DSA) and Phaseolus vulgaris leukoagglutinating lectin] were monitored in real-time with the change in the SPR response. Of these lectins, only RCA120 and DSA showed an increase in the SPR response, indicating that these two lectins bound specifically to the immobilized glycopeptide. The other lectins did not show any significant changes in the SPR response. These results are in good agreement with the binding specificity previously demonstrated with affinity chromatography. The association-rate constant (kass) and the dissociation-rate constant (kdiss) for the glycopeptide-RCA120 interaction were 3.4 x 10(5) M-1 s-1 and 2.1 x 10(-3) s-1, respectively. The kass and kdiss determined for DSA were 5.7 x 10(5) M-1 s-1 and 1.3 x 10(-3) s-1, respectively. Furthermore, the relative binding molar ratio to the glycopeptide was three times higher for RCA120 than for DSA, suggesting that this sugar chain possesses three binding sites for RCA120 and one for DSA. These parameters are expected to provide useful information for defining the interaction between oligosaccharides and lectins.