Application of reinforced frontal affinity chromatography and advanced processing procedure to the study of the binding property of a Caenorhabditis elegans galectin

Transformation of Agrocybe cylindracea Galectin into αGalNAc-Specific Lectin

A multi-specific fungal galectin from the mushroom Agrocybe cylindracea (ACG) binds a broad range of β-galactosides, as well as their derivative GalNAcα1-3Gal. Site-directed mutagenesis of the hydrophilic residues His, Asn, Arg, and Glu, involved in carbohydrate recognition, abolished the binding affinity of the derived mutants to β-galactosides, whereas only N46A caused increased affinity to GalNAcα1-3Gal-containing oligosaccharides and loss of β-galactoside-binding activity. Detailed structural analysis revealed that Pro45, the preceding residue of Asn46 of the wild-type ACG, takes the cis imide conformation to tether Asn46 onto a loop region to make new hydrogen bonds with β-galactosides and to compensate for the lack of evolutionarily conserved Asn. In contrast, in the N46A mutant, Pro45 takes the more stable trans conformation, resulting in "switched" specificity to αGalNAc. Such an altered recognition system in the binding specificity of galectins can be observed in other lectin molecules not only in nature but will also be observed in those engineered in the future.

Frontal affinity chromatography: An excellent method of analyzing weak biomolecular interactions based on a unique principle

BACKGROUND

Not only strong biomolecular interactions but also weak interactions play important roles in ensuring appropriate operations of many biological systems. Although a thorough investigation of the latter is essential in understanding life science, few suitable research tools are available because of inherent difficulties.

SCOPE OF REVIEW

Frontal affinity chromatography (FAC) is a versatile method that overcomes the inherent difficulties to provide accurate information on weak interactions. Since its concept and merit are not widely recognized, a comprehensive interpretation of FAC is provided in this review to encourage its application among researchers.

MAJOR CONCLUSION

FAC is based on a unique principle of measuring the binding strength by the delayed migration of an analyte through an affinity column. Its utility was elucidated via the lectin-glycan interactions.

GENERAL SIGNIFICANCE

FAC has a great potential as a research tool to solve many difficult problems in general bioscience that are relevant to almost all researchers.

Overview of Characterizing Cancer Glycans with Lectin-Based Analytical Methods

Glycosylation is a post-translational modification that is often altered in disease development and progression, including cancer. In cancerous patients, the abnormal expression of glycosylation enzymes leads to aberrant glycosylation, which has been linked to malignant tissues. Due to aberrant glycosylation, the presence of specific glycans can be used as biomarkers for identifying the type and stage of cancer. Glycan structures are heterogeneous, with different protein glycoforms having different functional activities. Lectins are an important tool in glycan analysis due to their specificity in binding to unique glycan linkages and monosaccharide units, which allows for the identification of unique glycan structural properties. In this review, we will discuss the use of lectins in microarrays and chromatography for characterizing glycan structures.

MCAW-DB: A glycan profile database capturing the ambiguity of glycan recognition patterns

Glycan-binding protein (GBP) interaction experiments, such as glycan microarrays, are often used to understand glycan recognition patterns. However, oftentimes the interpretation of glycan array experimental data makes it difficult to identify discrete GBP binding patterns due to their ambiguity. It is known that lectins, for example, are non-specific in their binding affinities; the same lectin can bind to different monosaccharides or even different glycan structures. In bioinformatics, several tools to mine the data generated from these sorts of experiments have been developed. These tools take a library of predefined motifs, which are commonly-found glycan patterns such as sialyl-Lewis X, and attempt to identify the motif(s) that are specific to the GBP being analyzed. In our previous work, as opposed to using predefined motifs, we developed the Multiple Carbohydrate Alignment with Weights (MCAW) tool to visualize the state of the glycans being recognized by the GBP under analysis. We previously reported on the effectiveness of our tool and algorithm by analyzing several glycan array datasets from the Consortium of Functional Glycomics (CFG). In this work, we report on our analysis of 1081 data sets which we collected from the CFG, the results of which we have made publicly and freely available as a database called MCAW-DB. We introduce this database, its usage and describe several analysis results. We show how MCAW-DB can be used to analyze glycan-binding patterns of GBPs amidst their ambiguity. For example, the visualization of glycan-binding patterns in MCAW-DB show how they correlate with the concentrations of the samples used in the array experiments. Using MCAW-DB, the patterns of glycans found to bind to various GBP-glycan binding proteins are visualized, indicating the binding "environment" of the glycans. Thus, the ambiguity of glycan recognition is numerically represented, along with the patterns of monosaccharides surrounding the binding region. The profiles in MCAW-DB could potentially be used as predictors of affinity of unknown or novel glycans to particular GBPs by comparing how well they match the existing profiles for those GBPs. Moreover, as the glycan profiles of diseased tissues become available, glycan alignments could also be used to identify glycan biomarkers unique to that tissue. Databases of these alignments may be of great use for drug discovery.

Frontal affinity chromatography: a unique research tool for biospecific interaction that promotes glycobiology

Combination of bioaffinity and chromatography gave birth to affinity chromatography. A further combination with frontal analysis resulted in creation of frontal affinity chromatography (FAC). This new versatile research tool enabled detailed analysis of weak interactions that play essential roles in living systems, especially those between complex saccharides and saccharide-binding proteins. FAC now becomes the best method for the investigation of saccharide-binding proteins (lectins) from viewpoints of sensitivity, accuracy, and efficiency, and is contributing greatly to the development of glycobiology. It opened a door leading to deeper understanding of the significance of saccharide recognition in life. The theory is also concisely described.

Lectin-based glycomics: how and when was the technology born?

Lectin-based glycomics is an emerging, comprehensive technology in the post-genome sciences. The technique utilizes a panel of lectins, which is a group of biomolecules capable of deciphering "glycocodes," with a novel platform represented by a lectin microarray. The method enables multiple glycan-lectin interaction analyses to be made so that differential glycan profiling can be performed in a rapid and sensitive manner. This approach is in clear contrast to another advanced technology, mass spectrometry, which requires prior glycan liberation. Although the lectin microarray cannot provide definitive structures of carbohydrates and their attachment sites, it gives useful clues concerning the characteristic features of glycoconjugates. These include differences not only in terminal modifications (e.g., sialic acid (Sia) linkage, types of fucosylation) but also in higher ordered structures in terms of glycan density, depth, and direction composed for both N- and O-glycans. However, before this technique began to be implemented in earnest, many other low-throughput methods were utilized in the late twentieth century. In this chapter, the author describes how the current lectin microarray technique has developed based on his personal experience.

Identification of a second, non-conserved amino acid that contributes to the unique sugar binding properties of the nematode galectin LEC-1

The basic disaccharide structure recognized by galectin family members is the lactosamine-like structure Galbeta1-4(3)Glc(NAc). The 32-kDa galectin LEC-1 of the nematode Caenorhabditis elegans is composed of two domains, each of which is homologous to vertebrate 14-kDa-type galectins. The N-terminal lectin domain of LEC-1 recognizes blood group A saccharide (GalNAcalpha1-3(Fucalpha1-2)Galbeta1-3GlcNAc), whereas this saccharide is poorly recognized by the C-terminal domain. Using a combination of site-directed mutagenesis and analysis of the sugar-binding profile by frontal affinity chromatography, we previously found that Thr41 in the N-terminal lectin domain of LEC-1 is important for its affinity for A-hexasaccharide. Thr41 is located on beta-strand S3, next to the three beta-strands S4-S6, where the conserved amino acids form the binding site for the basic Galbeta1-4(3)Glc(NAc) structure. Here, we report that a second amino acid, Asp133, in the N-terminal lectin domain of LEC-1, located on the beta-strand S2 adjacent to that containing Thr41, is important for LEC-1-specific recognition of A-hexasaccharide. These results suggest that amino acid residues other than those located on the three beta-strands S4-S6, contribute to the unique sugar binding specificity of individual galectins.

Frontal affinity chromatography: sugar-protein interactions

Frontal affinity chromatography using fluorescence detection (FAC-FD) is a versatile technique for the precise determination of dissociation constants (Kd) between glycan-binding proteins (lectins) and fluorescent-labeled glycans. A series of glycan-containing solutions is applied to a lectin-immobilized column, and the elution profile of each glycan (termed the 'elution front', V) is compared with that (V0) for an appropriate control. Here we describe our standard protocol using an automated FAC system (FAC-1), consisting of two isocratic pumps, an autosampler, a column oven and two miniature columns connected to a fluorescence detector. Analysis time for 100 sugar-protein interactions is approximately 10 h, using as little as 2.5 pmol of pyridylaminated (PA) oligosaccharide per analysis. Using FAC-FD, we have so far obtained quantitative interaction data of >100 lectins for >100 PA oligosaccharides.

Identification of the amino acid residue in the nematode galectin LEC-1 responsible for its unique sugar binding property: analysis by combination of site-directed mutagenesis and frontal affinity chromatography

The basic disaccharide structure recognized by galectin family members is the lactosamine-like structure Galbeta1-4(3)Glc(NAc). In galectins, eight highly conserved amino acid residues participate in the recognition of this basic structure. Each galectin seems to mediate diverse biological functions due to recognition of different modifications of the basic disaccharide Galbeta1-4(3)Glc(NAc), but there is very little information about which amino acid residue in galectin is responsible for recognizing these modifications. The 32-kDa galectin LEC-1 of the nematode Caenorhabditis elegans is composed of two domains, each of which is homologous to vertebrate 14-kDa-type galectins. Although both lectin domains have an affinity for N-acetyllactosamine (Galbeta1-4GlcNAc)-containing, N-linked, complex-type sugar chains, the N-terminal lectin domain of LEC-1 recognizes blood group A saccharide (GalNAcalpha1-3(Fucalpha1-2)Galbeta1-3GlcNAc), whereas this saccharide is only poorly recognized by the C-terminal domain. Here, we used a combination of site-directed mutagenesis of the N-terminal lectin domain of galectin LEC-1 and an analysis of the sugar-binding profile by frontal affinity chromatography to identify the amino acid residues important for this recognition. Our results indicate that Thr(41) in the N-terminal lectin domain of LEC-1 is important for its affinity for A-hexasaccharide.

Phylogenetic and specificity studies of two-domain GNA-related lectins: generation of multispecificity through domain duplication and divergent evolution

A re-investigation of the occurrence and taxonomic distribution of proteins built up of protomers consisting of two tandem arrayed domains equivalent to the GNA [Galanthus nivalis (snowdrop) agglutinin] revealed that these are widespread among monotyledonous plants. Phylogenetic analysis of the available sequences indicated that these proteins do not represent a monophylogenetic group but most probably result from multiple independent domain duplication/in tandem insertion events. To corroborate the relationship between inter-domain sequence divergence and the widening of specificity range, a detailed comparative analysis was made of the sequences and specificity of a set of two-domain GNA-related lectins. Glycan microarray analyses, frontal affinity chromatography and surface plasmon resonance measurements demonstrated that the two-domain GNA-related lectins acquired a marked diversity in carbohydrate-binding specificity that strikingly contrasts the canonical exclusive specificity of their single domain counterparts towards mannose. Moreover, it appears that most two-domain GNA-related lectins interact with both high mannose and complex N-glycans and that this dual specificity relies on the simultaneous presence of at least two different independently acting binding sites. The combined phylogenetic, specificity and structural data strongly suggest that plants used domain duplication followed by divergent evolution as a mechanism to generate multispecific lectins from a single mannose-binding domain. Taking into account that the shift in specificity of some binding sites from high mannose to complex type N-glycans implies that the two-domain GNA-related lectins are primarily directed against typical animal glycans, it is tempting to speculate that plants developed two-domain GNA-related lectins for defence purposes.

The Sclerotinia sclerotiorum agglutinin represents a novel family of fungal lectins remotely related to the Clostridium botulinum non-toxin haemagglutinin HA33/A

Previous studies indicated that sclerotes of the phytopathogenic Ascomycete Sclerotinia sclerotiorum contain a lectin that based on its molecular structure, specificity and N-terminal amino acid sequence could not be classified yet into any lectin family. Using a combination of molecular cloning, frontal affinity chromatography and molecular modelling the identity of the S. sclerotiorum agglutinin (SSA) was analyzed. Molecular cloning demonstrated that SSA shares no sequence similarity with any known fungal lectin or protein. The lectin is synthesized as a 153 amino acid polypeptide without signal peptide and undergoes apart from the removal of the N-terminal methionine no further processing. Frontal affinity chromatography revealed that the binding site of SSA primarily accommodates a non-reducing terminal GalNAc with a preference for the alpha- over the beta-anomer. SSA also strongly interacts with both glycolipid type glycans with terminal non-reducing Gal or GalNAc and galactosylated N-glycans. SSA shares a residual sequence similarity with part of the non-toxin haemagglutinin HA33/A from Clostridium botulinum. Molecular modeling using the three-dimensional structure of HA33/A as a template indicated that SSA can fold into a similar beta-trefoil domain. Though these results should be interpreted with care it is tempting to speculate that the Sclerotiniaceae lectins thus appear to be structurally related to the ricin-B superfamily. All evidence suggests that SSA represents a novel family of fungal lectins with a unique sequence and sugar-binding properties. Taking into account that orthologues of SSA are fairly common within the family Sclerotiniaceae but could not be identified in any other fungal species one can reasonably conclude that SSA-type lectins are confined to a small taxonomic group of the Ascomycota.

Preparation of a monolithic capillary column with immobilized α-mannose for affinity chromatography of lectins

A simple method for the preparation of an affinity monolithic (also called continuous bed) capillary column for alpha-mannose-specific lectins is described. 2-Hydroxyethyl methacrylate in combination with (+)-N,N -diallyltartardiamide (DATD) and piperazine diacrylamide (PDA, 1,4-bisacryloyl-piperazine) as crosslinkers, were used as monomers for the monolith. After oxidation of DATD with periodate, alpha-mannose with spacer was bound to the aldehyde groups of the polymeric skeleton via reductive amination to form an affinity column for the separation, enrichment or binding studies of mannose-specific lectins. The permeability of the column was excellent. The porosity of the monolith was investigated by scanning electron microscope (SEM) and inverse size exclusion chromatography (ISEC). The affinity of the monolith was evaluated by frontal analysis (FA) and fluorescence microscopy (FM) using fluorescently labeled concanavalin (Con A). Frontal affinity chromatography showed a specific interaction of two different lectins with the alpha-mannose-modified monolith. According to FM the affinity sites were evenly distributed over the monolithic bed.

A Combined Strategy for Glycan Profiling: a Model Study with Pyridylaminated Oligosaccharides

Structural glycomics plays a fundamental role in glycoscience and glycotechnology. In this paper, a novel strategy for the structural characterization of glycans is described, in which MS2 analysis involving a LIFT-TOF/TOF procedure is combined with frontal affinity chromatography (FAC). As model compounds, 20 neutral pyridylaminated (PA) oligosaccharides were chosen, which included four groups of structural isomers differing in sequence, linkage, position, or branching features. By depicting significant diagnostic ions on MS2, most of the analyzed oligosaccharides were successfully differentiated, while two pairs of linkage isomers, i.e., LNT/LNnT, and LNH/LNnH were not. For subsequent analysis by FAC, 14 lectins showing significant affinity to either LNT (type 1) or LNnT (type 2) were screened, and a galectin from the marine sponge Geodia cydonium (GC1) and a plant seed lectin from Ricinus communis (RCA-I) were used for determination of type 1 and 2 chains, respectively. With these specific probes, both of the isomeric pairs were unambiguously differentiated. Furthermore, a pair of triantennary, asparagine-linked oligosaccharide isomers could also be successfully differentiated. Thus, the combination of MS2 and FAC is a practical alternative for the structural characterization of complex glycans.

Comparative analysis by frontal affinity chromatography of oligosaccharide specificity of GlcNAc-binding lectins, Griffonia simplicifolia lectin-II (GSL-II) and Boletopsis leucomelas lectin (BLL)

Lectin-based structural glycomics requires a search for useful lectins and their biochemical characterization to profile complex features of glycans. In this paper, two GlcNAc-binding lectins are reported with their detailed oligosaccharide specificity. One is a classic plant lectin, Griffonia simplicifolia lectin-II (GSL-II), and the other is a novel fungal lectin, Boletopsis leucomelas lectin (BLL). Their sugar-binding specificity was analyzed by frontal affinity chromatography using 146 glycans (125 pyridylaminated and 21 p-nitrophenyl saccharides). As a result, it was found that both GSL-II and BLL showed significant affinity toward complex-type N-glycans, which are either partially or completely agalactosylated. However, their branch-specific features differed significantly: GSL-II strongly bound to agalacto-type, tri- or tetra-antennary N-glycans with its primary recognition of a GlcNAc residue transferred by GlcNAc-transferase IV, while BLL preferred N-glycans with fewer branches. In fact, the presence of a GlcNAc residue transferred by GlcNAc-transferase V abolishes the binding of BLL. Thus, GSL-II and BLL forms a pair of complementally probes to profile a series of agalacto-type N-glycans.

Evidence that Agaricus bisporus agglutinin (ABA) has dual sugar-binding specificity

Agaricus bisporus agglutinin (ABA) is known as a useful lectin to detect T-antigen (Core1) disaccharide (Galbeta1-3GalNAcalpha) and related O-linked glycans. However, a recent X-ray crystallographic study revealed the presence of another intrinsic sugar-binding site, i.e., for GlcNAc. To confirm this possibility, detailed analysis was performed using two advanced methods: lectin microarray and frontal affinity chromatography (FAC). In the lectin microarray, intense signals were observed on ABA spots for both N-glycanase-treated and O-glycanase/beta1-4galactosidase-treated Cy3-labeled asialofetuin. This indicates substantial affinity for both O-linked and agalactosylated (GlcNAc-exposed) N-linked glycans. A further approach by FAC using 20 pNP and 130 PA-oligosaccharides demonstrated that ABA bound to Core1 (K(d) = 3.4 x 10(-6) M) and Core2 (1.9 x 10(-5) M) but not to Core3 and Core6 O-linked glycans. It also showed substantial affinity to mono-, bi-, and tri-antennary agalactosylated complex-type N-linked glycans (K(d) > 1.8 x 10(-5) M). These results establish ABA as a lectin having dual sugar-binding sites with distinct specificity, i.e., for Gal-exposed O-linked glycans and GlcNAc-exposed N-linked glycans.

High-throughput analysis of lectin-oligosaccharide interactions by automated frontal affinity chromatography

Frontal affinity chromatography (FAC) is a quantitative method that enables sensitive and reproducible measurements of interactions between lectins and oligosaccharides. The method is suitable even for the measurement of low-affinity interactions and is based on a simple procedure and a clear principle. To achieve high-throughput and efficient analysis, an automated FAC system was developed. The system designated FAC-1 consists of two isocratic pumps, an autosampler, and a couple of miniature columns (bed volume, 31.4 microl) connected in parallel to either a fluorescence or an ultraviolet detector. By use of this parallel-column system, the time required for each analysis was reduced substantially. Under the established conditions, fewer than 10 hrs are required for 100 interaction analyses, consuming as little as 1 pmol pyridylaminated oligosaccharide for each analysis. This strategy for FAC should contribute to the construction of a lectin-oligosaccharide interaction database essential for future glycomics. Overall features and practical protocols for interaction analyses using FAC-1 are described.

Lectin-based structural glycomics: glycoproteomics and glycan profiling

Structural glycomics (SG) plays a fundamental part of concurrent glycobiology aiming at comprehensive elucidation of glycan functions ( i.e. , functional glycomics) in the context of post-genome sciences. The SG project started in April 2003 and will continue for 3 years in the framework of NEDO (New Energy and Industrial Technology Organization) under the METI (the Ministry of Economy, Trade, and Industry), Japan. The main purpose of the project is the development of high-throughput and robust machines, which should greatly contribute to the structural analysis of complex glycans. In this chapter, 2 major research items, i.e. , (1) glycoproteomics, which enables comprehensive analysis of glycoproteins, and (2) "glycan profiling" by means of lectins, are described. For the latter, frontal affinity chromatography has been adopted as a starting tool for comprehensive analysis of the interaction of 100 lectins and 100 oligosaccharides under the concept of "hect-by-hect," which refers to 100 x 100.

Frontal immunoaffinity chromatography with mass spectrometric detection: a method for finding active compounds from traditional Chinese herbs

Frontal affinity chromatography (FAC) using immobilized polyclone antibodies of compound A coupled with mass spectrometry was used for the screening of affinity compounds from an extract of Phyllanthus urinaria L. Mass spectrometry was used as an analyzer of FAC. It can analyze the frontal affinity chromatogram of each compound of the extract in one program. The extract was dissolved in 2 mM NH4OAc at a concentration of 10 microg/ mL, then loaded on the immobilized antibody column, and data were collected from mass spectrometry to get a frontal affinity chromatogram. The screening of extract resulted in brevifolin, brevifolin carboxylic acid, corilagin, ellagic acid, and phyllanthusiin U. Activity analyses give high inhibitory activities to these compounds. This research work afforded us a new approach to find new leading compounds from nature or a man-made combinatorial library that have different structure styles or to find substitutes for the synthetic active compound that has high toxicity.

Frontal Affinity Chromatography Combined On-Line with Mass Spectrometry: A Tool for the Binding Study of Different Epidermal Growth Factor Receptor Inhibitors

Frontal affinity chromatography (FAC) is a simple but powerful method to analyze molecular interactions between an analyte and an immobilized ligand by calculating the extent of retardation of the elution front. By combination of FAC with a PE-Mariner electrospray ionization mass spectrometry, a very efficient and straightforward procedure was developed herein for analyzing the binding properties of different inhibitors of the epidermal growth factor receptor (EGFR). In this study, a polyclonal antibody prepared with a known anti-EGFR inhibitor coupled with bovine serum albumin was adopted as the stationary phase in the FAC system. Using the antibody to mimic the receptor, other different anti-EGFR inhibitors as well as the small-molecule half-antigen itself were recognized directly from the crude extract of herb, which afforded us a novel promising approach for the efficient screening of lead compounds or drug candidates from natural resources.

Oligosaccharide specificity of galectins: a search by frontal affinity chromatography

Galectins are widely distributed sugar-binding proteins whose basic specificity for beta-galactosides is conserved by evolutionarily preserved carbohydrate-recognition domains (CRDs). Although they have long been believed to be involved in diverse biological phenomena critical for multicellular organisms, in only few a cases has it been proved that their in vivo functions are actually based on specific recognition of the complex carbohydrates expressed on cell surfaces. To obtain clues to understand the physiological roles of diverse members of the galectin family, detailed analysis of their sugar-binding specificity is necessary from a comparative viewpoint. For this purpose, we recently reinforced a conventional system for frontal affinity chromatography (FAC) [J. Chromatogr., B, Biomed. Sci. Appl. 771 (2002) 67-87]. By using this system, we quantitatively analyzed the interactions at 20 degrees C between 13 galectins including 16 CRDs originating from mammals, chick, nematode, sponge, and mushroom, with 41 pyridylaminated (PA) oligosaccharides. As a result, it was confirmed that galectins require three OH groups of N-acetyllactosamine, as had previously been denoted, i.e., 4-OH and 6-OH of Gal, and 3-OH of GlcNAc. As a matter of fact, no galectin could bind to glycolipid-type glycans (e.g., GM2, GA2, Gb3), complex-type N-glycans, of which both 6-OH groups are sialylated, nor Le-related antigens (e.g., Le(x), Le(a)). On the other hand, considerable diversity was observed for individual galectins in binding specificity in terms of (1) branching of N-glycans, (2) repeating of N-acetyllactosamine units, or (3) substitutions at 2-OH or 3-OH groups of nonreducing terminal Gal. Although most galectins showed moderately enhanced affinity for branched N-glycans or repeated N-acetyllactosamines, some of them had extremely enhanced affinity for either of these multivalent glycans. Some galectins also showed particular preference for alpha1-2Fuc-, alpha1-3Gal-, alpha1-3GalNAc-, or alpha2-3NeuAc-modified glycans. To summarize, galectins have evolved their sugar-binding specificity by enhancing affinity to either "branched", "repeated", or "substituted" glycans, while conserving their ability to recognize basic disaccharide units, Galbeta1-3/4GlcNAc. On these bases, they are considered to exert specialized functions in diverse biological phenomena, which may include formation of local cell-surface microdomains (raft) by sorting glycoconjugate members for each cell type.

Separation technologies for glycomics

Progress in genome projects has provided us with fundamentals on genetic information; however, the functions of a large number of genes remain to be elucidated. To understand the in vivo functions of eukaryotic genes, it is essential to grasp the features of their post-translational modifications. Among them, protein glycosylation is a central issue to be discussed, considering the predominant roles of glycoproteins in cell-cell and cell-substratum recognition events in multicellular organisms. In this context, it is necessary to establish a core strategy for analyzing glycosylated proteins under the concept of the "glycome" [Trends Glycosci. Glycotechnol. 12 (2000) 1]. Though the term glycome should be defined, in analogy to the genome and proteome, as "a whole set of glycans produced in a single organism", here we propose a glycome project specifically focusing on glycoproteins. Principal objectives in the project are to identify: (1) which genes encode glycoproteins (i.e. genome information); (2) which sites among potential glycosylation sites are actually glycosylated (i.e. glycosylation site information); (3) what are the structures of glycans (i.e. structural information); and (4) what are the effects (functions) of glycosylation (functional information). For these purposes, two affinity technologies have been introduced. One is named the "glyco-catch method" to identify genes encoding glycoproteins [Proteomics 1 (2001) 295], and the other is the recently reinforced "frontal affinity chromatography" [J. Chromatogr. A 890 (2000) 261]. By the former method, genes that encode glycoproteins as well as glycosylation sites are systematically identified by the efficient combination of conventional lectin-affinity chromatography and contemporary in silico database searching. The following three actions have been devised for rapid and systematic characterization of glycans: (1) mass spectrometry to acquire exact mass information; (2) 2-D/3-D mapping to obtain refined chemical information; and (3) reinforced frontal affinity chromatography to determine affinity constants (K(a)-values) for a set of lectins. Pyridylaminated glycans are used throughout the characterization processes. In this review, the concept and strategy of glycomic approaches are described referring to the on-going glycome project focused on the nematode Caenorhabditis elegans.

Adsorption kinetics of beta-lactoglobulin on a polyclonal immunochromatographic support

Beta-Lactoglobulin is one of the main components of whey proteins. Among other reasons, its allergenicity makes its determination in hypoallergenic foods and bio-pharmaceutical products necessary. Immunoaffinity chromatography is a widely accepted technique for purification and analysis of proteins. Knowledge of the apparent kinetics of the adsorption of beta-lactoglobulin onto the anti-beta-lactoglobulin immunochromatographic column is important to optimize the analytical process. High-performance frontal affinity chromatography was used to study the apparent kinetics of the adsorption process. Langmuir and bi-Langmuir kinetic models, assuming one and two kinds of binding sites, respectively, were used to characterize the adsorption kinetics of beta-lactoglobulin B on a polyclonal immunoadsorbent. Very good fits were obtained with the bi-Langmuir model for two different concentrations of beta-lactoglobulin and this allowed us to calculate the apparent adsorption rate constants and the column capacities for both kinds of sites. Experimental results indicate the possibility that the adsorption process is not irreversible. The values of the apparent dissociation rate constants leading to the best fit were estimated and the affinity constants were calculated.

Sugar binding properties of the two lectin domains of the tandem repeat-type galectin LEC-1 (N32) of Caenorhabditis elegans. Detailed analysis by an improved frontal affinity chromatography method

The 32-kDa galectin (LEC-1 or N32) of the nematode Caenorhabditis elegans is the first example of a tandem repeat-type galectin and is composed of two domains, each of which is homologous to typical vertebrate 14-kDa-type galectins. To elucidate the biological meaning of this unique structure containing two probable sugar binding sites in one molecule, we analyzed in detail the sugar binding properties of the two domains by using a newly improved frontal affinity chromatography system. The whole molecule (LEC-1), the N-terminal lectin domain (Nh), and the C-terminal lectin domain (Ch) were expressed in Escherichia coli, purified, and immobilized on HiTrap gel agarose columns, and the extent of retardation of various sugars by the columns was measured. To raise the sensitivity of the system, we used 35 different fluorescence-labeled oligosaccharides (pyridylaminated (PA) sugars). All immobilized proteins showed affinity for N-acetyllactosamine-containing N-linked complex-type sugar chains, and the binding was stronger for more branched sugars. Ch showed 2-5-fold stronger binding toward all complex-type sugars compared with Nh. Both Nh and Ch preferred Galbeta1-3GlcNAc to Galbeta1-4GlcNAc. Because the Fucalpha1-2Galbeta1-3GlcNAc (H antigen) structure was found to interact with all immobilized protein columns significantly, the K(d) value of pentasaccharide Fucalpha1-2Galbeta1-3GlcNAcbeta1-3Galbeta1-4Glc-PA for each column was determined by analyzing the concentration dependence. Obtained values for immobilized LEC-1, Nh, and Ch were 6.0 x 10(-5), 1.3 x 10(-4), and 6.5 x 10(-5) m, respectively. The most significant difference between Nh and Ch was in their affinity for GalNAcalpha1-3(Fucalpha1-2)Galbeta1-3GlcNAcbeta1-3Galbeta1-4Glc-PA, which contains the blood group A antigen; the K(d) value for immobilized Nh was 4.8 x 10(-5) m, and that for Ch was 8.1 x 10(-4) m. The present results clearly indicate that the two sugar binding sites of LEC-1 have different sugar binding properties.