Oligosaccharide Ligands of Galectin-4 and Its Subunits: Multivalency Scores Highly

A homogalacturonan-rich pectic polysaccharide isolated from Lonicera japonica Thunb. modulates galectin-4-mediated bioactivity and anti-hepatocellular carcinoma activity

L. japonica is a traditional Chinese medicine with dual-use properties. Herein, a HG-rich pectic polysaccharide, WLJP-03A, was purified from the dried flowers of L. japonica, which composed of Rha (5 %), GalA (60 %), Gal (5 %), and Ara (30 %), with a molecular weight of 28.1 kDa. WLJP-03A could be defined as an HG backbone with α-(1 → 3,5)-linked and α-(1 → 5)-linked arabinan, β-(1 → 3,6)-linked and β-(1 → 3)-linked galactan, and type II arabinogalactan side chains. Its interaction with two truncated structural domain proteins of galectin-4 (Gal-4) revealed stronger binding of WLJP-03A to Gal-4C (MIC = 15 μg/mL) than to Gal-4N (MIC = 62 μg/mL), indicating that WLJP-03A mainly interacted with the C-terminal CRD to inhibit the biological activity of Gal-4. Furthermore, in vitro antitumor assays showed that WLJP-03A could inhibit the cellular proliferation and migration of HCCLM3 cells induced by Gal-4. These results provide new insights into the structure-activity relationship between L. japonica polysaccharide and Gal-4.

Characterization of HOL-30: a novel tandem-repeat galectin from the marine sponge Halichondria okadai

We here report the novel primary structure of a new member in the galectin family, the β-galactoside-binding lectin HOL-30, from the marine sponge Halichondria okadai, whose full-length sequence was determined thanks to the combination between Edman degradation and transcriptome analysis. The HOL-30 polypeptide is a tandem-repeat dimeric galectin, consisting of 281 amino acids, which includes two carbohydrate recognition domains (CRDs). Unlike most other galectins described in Porifera, HOL-30 did not have a signal peptide sequence for secretion. In solution, HOL-30 exhibited a molecular weight of 60 kDa, indicating a dimeric organization consisting of two 30 kDa tandem-repeat subunits stabilized by non-covalent interactions. Although the two CRDs had a similar predicted 3D structure, they displayed low pairwise sequence identity, approximately 20 %. HOL-30 exhibited glycan-binding affinities for type-1 (Galβ1-3GlcNAc) and type-2 (Galβ1-4GlcNAc) LacNAc. Furthermore, it also recognized blood type B-oligosaccharides on type-1 and type-2 LacNAc (Galα1-3Gal[Fucα1-2]β1-3/4GlcNAc), and blood type H-oligosaccharide on type-3 (Gal[Fucα1-2]β1-3GalNAcα). The glycan-binding properties of HOL-30 were compared with those of the hRTL galectin, previously identified in Chondrilla australiensis, consisting of tetrameric 15 kDa prototype subunits. The two sponge galectins displayed similar, but not identical, carbohydrate-binding properties, as evidenced by the fact that despite effectively binding to vertebrate cultured cells, HOL-30 had minimal impact on cell growth. Antiserum analysis revealed a mosaic distribution of HOL-30 in the parenchymal cells of sponge tissues within dense cell clusters surrounding the spicules.

Color-coded galectin fusion proteins as novel tools in biomaterial science

The inherent carbohydrate-binding specificities of human galectins can serve as recognition elements in both biotechnological and biomedical applications. The combination of the carbohydrate-recognition domain (CRD) of galectins fused to peptides or proteins for purification, immobilization, and imaging enables multifunctional utilization within a single protein. We present here a library of color-coded galectin fusion proteins that incorporate a His6-tag, a fluorescent protein, and a SpyCatcher or SpyTag unit to enable immobilization procedures. These galectin fusion proteins exhibit similar binding properties to the non-fused galectins with micromolar apparent binding affinities. N- and C-terminal fusion partners do not interfere with the SpyCatcher/SpyTag immobilization. By applying SpyCatcher/SpyTag-mediated SC-ST-Gal-3 conjugates, we show the stepwise formation of a three-layer ECM-like structure in vitro. Additionally, we demonstrate the SpyCatcher/SpyTag-mediated immobilization of galectins in microgels, which can serve as a transport platform for localized targeting applications. The proof of concept is provided by the galectin-mediated binding of microgels to colorectal cancer cells.

High expression of B3GALT5 suppresses the galectin-4-mediated peritoneal dissemination of poorly differentiated gastric cancer cells

Peritoneal metastasis frequently accompanies metastatic and/or recurrent gastric cancer, leading to a poor prognosis owing to a lack of effective treatment. Hence, there is a pressing need to enhance our understanding of the mechanisms and molecules driving peritoneal metastasis. In a previous study, galectin-4 inhibition impeded peritoneal metastasis in a murine model. This study examined the glycan profiles of cell surface proteins and glycosphingolipids (GSLs) in cells with varying tumorigenic potentials to understand the intricate mechanisms underlying galectin-4-mediated regulation, particularly glycosylation. Detailed mass spectrometry analysis showed that galectin-4 knockout cells exhibit increased expression of lacto-series GSLs with β1,3-linked galactose while showing no significant alterations in neolacto-series GSLs. We conducted real-time polymerase chain reaction (PCR) analysis to identify candidate glycosyltransferases that synthesize increased levels of GSLs. Subsequently, we introduced the candidate B3GALT5 gene and selected the clones with high expression levels. B3GALT5 gene-expressing clones showed GSL glycan profiles like those of knockout cells and significantly reduced tumorigenic ability in mouse models. These clones exhibited diminished proliferative capacity and showed reduced expression of galectin-4 and activated AKT. Moreover, co-localization of galectin-4 with flotillin-2 (a raft marker) decreased in B3GALT5-expressing cells, implicating GSLs in galectin-4 localization to lipid rafts. D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (a GSL synthase inhibitor) also affected galectin-4 localization in rafts, suggesting the involvement of GSL microdomains. We discovered that B3GALT5 plays a crucial role in regulating peritoneal metastasis of malignant gastric cancer cells by suppressing cell proliferation and modulating lipid rafts and galectin-4 via mechanisms that are yet to be elucidated.

Different roles of the heterodimer architecture of galectin-4 in selective recognition of oligosaccharides and lipopolysaccharides having ABH antigens

The dimeric architecture of tandem-repeat type galectins, such as galectin-4 (Gal-4), modulates their biological activities, although the underlying molecular mechanisms have remained elusive. Emerging evidence show that tandem-repeat galectins play an important role in innate immunity by recognizing carbohydrate antigens present on the surface of certain pathogens, which very often mimic the structures of the human self-glycan antigens. Herein, we have analyzed the binding preferences of the C-domain of Gal-4 (Gal-4C) toward the ABH-carbohydrate histo-blood antigens with different core presentations and their recognition features have been rationalized by using a combined experimental approach including NMR, solid-phase and hemagglutination assays, and molecular modeling. The data show that Gal-4C prefers A over B antigens (two-fold in affinity), contrary to the N-domain (Gal-4N), although both domains share the same preference for the type-6 presentations. The behavior of the full-length Gal-4 (Gal-4FL) tandem-repeat form has been additionally scrutinized. Isothermal titration calorimetry and NMR data demonstrate that both domains within full-length Gal-4 bind to the histo-blood antigens independently of each other, with no communication between them. In this context, the heterodimeric architecture does not play any major role, apart from the complementary A and B antigen binding preferences. However, upon binding to a bacterial lipopolysaccharide containing a multivalent version of an H-antigen mimetic as O-antigen, the significance of the galectin architecture was revealed. Indeed, our data point to the linker peptide domain and the F-face of the C-domain as key elements that provide Gal-4 with the ability to cross-link multivalent ligands, beyond the glycan binding capacity of the dimer.

Microgels with Immobilized Glycosyltransferases for Enzymatic Glycan Synthesis

Glycans, composed of linked monosaccharides, play crucial roles in biology and find diverse applications. Enhancing their enzymatic synthesis can be achieved by immobilizing enzymes on materials such as microgels. Here, we present microgels with immobilized glycosyltransferases, synthesized through droplet microfluidics, immobilizing enzymes either via encapsulation or postattachment. SpyTag-SpyCatcher interaction was used for enzyme binding, among others. Fluorescamine and permeability assays confirmed enzyme immobilization and microgel porosity, while enzymatic activities were determined using HPLC. The potential application of microgels in cascade reactions involving multiple enzymes was demonstrated by combining β4GalT and α3GalT in an enzymatic reaction with high yields. Moreover, a cascade of β4GalT and β3GlcNAcT was successfully implemented. These results pave the way toward a modular membrane bioreactor for automated glycan synthesis containing the presented biocatalytic microgels.

Glycomimetic inhibitors of tandem-repeat galectins: Simple and efficient

The binding of human galectins by glycomimetic inhibitors is a promising therapeutic approach. The structurally distinct group of tandem-repeat galectins has scarcely been studied so far, and there is hardly any knowledge on their ligand specificity or their inhibitory potential, particularly concerning non-natural carbohydrates. Here, we present the synthesis of a library of seven 3-O-disubstituted thiodigalactoside-derived glycomimetics and their affinity to two tandem-repeat galectins, Gal-8 and Gal-9. The straightforward synthesis of these glycomimetics involved dibutyltin oxide-catalyzed 3,3́-O-disubstitution of commercially available unprotected thiodigalactoside, and conjugation of various aryl substituents by copper-catalyzed Huisgen azide-alkyne cycloaddition (CuAAC). The inhibitory potential of the prepared glycomimetics for Gal-8 and Gal-9 was assessed, and compared with the established galectins Gal-1 and Gal-3. The introduction of C-3 substituents resulted in an over 40-fold increase in affinity compared with unmodified TDG. The structure-affinity relations within the studied series were discussed using molecular modeling. Furthermore, the prepared glycomimetics were shown to scavenge Gal-8 and Gal-9 from the surface of cancer cells. This pioneering study on the synthetic inhibitors especially of Gal-9 identified lead compounds that may be used in further biomedical research.