Purification of galectin-1 mutants using an immobilized Galactoseβ1-4Fucose affinity adsorbent

Galectins are a family of lectins characterized by their carbohydrate recognition domains containing eight conserved amino acid residues, which allows the binding of galectin to β-galactoside sugars such as Galβ1-4GlcNAc. Since galectin-glycan interactions occur extracellularly, recombinant galectins are often used for the functional analysis of these interactions. Although it is relatively easy to purify galectins via affinity to Galβ1-4GlcNAc using affinity adsorbents such as asialofetuin-Sepharose, it could be difficult to do so with mutated galectins, which may have reduced affinity towards their endogenous ligands. However, this is not the case with Caenorhabditis elegans galectin LEC-6; binding to its endogenous recognition unit Galβ1-4Fuc, a unique disaccharide found only in invertebrates, is not necessarily affected by point mutations of the eight well-conserved amino acids. In this study, we constructed mutants of mouse galectin-1 carrying substitutions of each of the eight conserved amino acid residues (H44F, N46D, R48H, V59A, N61D, W68F, E71Q, and R73H) and examined their affinity for Galβ1-4GlcNAc and Galβ1-4Fuc. These mutants, except W68F, had very low affinity for asialofetuin-Sepharose; however, most of them (with the exception of H44F and R48H) could be purified using Galβ1-4Fuc-Sepharose. The affinity of the purified mutant galectins for glycans containing Galβ1-4Fuc or Galβ1-4GlcNAc moieties was quantitatively examined by frontal affinity chromatography, and the results indicated that the mutants retained the affinity only for Galβ1-4Fuc. Given that other mammalian galectins are known to bind Galβ1-4Fuc, our data suggest that immobilized Galβ1-4Fuc ligands could be generally used for easy one-step affinity purification of mutant galectins.

The Lectin Frontier Database (LfDB), and data generation based on frontal affinity chromatography

Lectins are a large group of carbohydrate-binding proteins, having been shown to comprise at least 48 protein scaffolds or protein family entries. They occur ubiquitously in living organisms—from humans to microorganisms, including viruses—and while their functions are yet to be fully elucidated, their main underlying actions are thought to mediate cell-cell and cell-glycoconjugate interactions, which play important roles in an extensive range of biological processes. The basic feature of each lectin’s function resides in its specific sugar-binding properties. In this regard, it is beneficial for researchers to have access to fundamental information about the detailed oligosaccharide specificities of diverse lectins. In this review, the authors describe a publicly available lectin database named “Lectin frontier DataBase (LfDB)”, which undertakes the continuous publication and updating of comprehensive data for lectin-standard oligosaccharide interactions in terms of dissociation constants (K_d’s). For K_d determination, an advanced system of frontal affinity chromatography (FAC) is used, with which quantitative datasets of interactions between immobilized lectins and >100 fluorescently labeled standard glycans have been generated. The FAC system is unique in its clear principle, simple procedure and high sensitivity, with an increasing number (>67) of associated publications that attest to its reliability. Thus, LfDB, is expected to play an essential role in lectin research, not only in basic but also in applied fields of glycoscience.

Biophysical characterization of lectin–glycan interactions for therapeutics, vaccines and targeted drug-delivery

Lectin–glycan interactions play a role in biological processes, host–pathogen interactions and in disease. A more detailed understanding of these interactions is not only useful for the elucidation of their biological function but can also be applied in immunology, drug development and delivery and diagnostics. We review some commonly used biophysical techniques for studying lectin–glycan interactions; namely: frontal affinity chromatography, glycan/lectin microarray, surface plasmon resonance, electrochemical impedance spectroscopy, isothermal titration calorimetry, fluorescent assays, enzyme linked lectin sorbent assay and saturation transfer difference nuclear magnetic resonance spectroscopy. Each method is evaluated on efficiency, cost and throughput. We also consider the advantages and limitations of each technique and provide examples of their application in biology, drug discovery and delivery, immunology, glycoprofiling and biosensing.

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.