Crystallization and preliminary crystallographic analysis of recombinant human galectin-1

Lactose-Functionalized Carbosilane Glycodendrimers Are Highly Potent Multivalent Ligands for Galectin-9 Binding: Increased Glycan Affinity to Galectins Correlates with Aggregation Behavior

Galectins, the glycan binding proteins, and their respective carbohydrate ligands represent a unique fundamental regulatory network modulating a plethora of biological processes. The advances in galectin-targeted therapy must be based on a deep understanding of the mechanism of ligand-protein recognition. Carbosilane dendrimers, the well-defined and finely tunable nanoscaffolds with low toxicity, are promising for multivalent carbohydrate ligand presentation to target galectin receptors. The study discloses a synthetic method for two types of lactose-functionalized carbosilane glycodendrimers (Lac-CS-DDMs). Furthermore, we report their outstanding, dendritic effect-driven affinity to tandem-type galectins, especially Gal-9. In the enzyme-linked immunosorbent assay, the affinity of the third-generation multivalent dendritic ligand bearing 32 lactose units to Gal-9 reached nanomolar values (IC50 = 970 nM), being a 1400-fold more effective inhibitor than monovalent lactose for this protein. This demonstrates a game-changing impact of multivalent presentation on the inhibitory effect of a ligand as simple as lactose. Moreover, using DLS hydrodynamic diameter measurements, we correlated the increased affinity of the glycodendrimer ligands to Gal-3 and Gal-8 but especially to Gal-9 with the formation of relatively uniform and stable galectin/Lac-CS-DDM aggregates.

A versatile strategy to synthesize N-methyl-anthranilic acid-labelled glycoprobes for fluorescence-based screening assays

Here we propose a general strategy to label carbohydrates with N-methyl-anthranilic acid to generate glycotools for fluorescence-based screening and carbohydrate–protein interaction studies.

Lactulose as a novel template for anticancer drug development targeting galectins

Galectins are carbohydrate binding proteins (lectins), which characteristically bind β-galactosides. Galectins play a role in tumour progression through involvement in proliferation, metastasis, angiogenesis, immune evasion and drug resistance. There is need for inhibitors (antagonists) that are specific for distinct galectins and that can interfere with galectin-carbohydrate interactions during cancer progression. Here, we propose that lactulose, a non-digestible galactose-fructose disaccharide, presents a novel inhibitor scaffold for design of inhibitors against galectins. Thermodynamic evaluation displays binding affinity of lactulose against the galectin-1 and galectin-3 carbohydrate recognition domain (CRD). Crystal structures of galectin-1 and galectin-3 in complex with lactulose reveal for the first time the molecular basis of the galectin-lactulose interactions. Molecular modelling was implemented to propose novel lactulose derivatives as potent anti-cancer agents.

CuAAC synthesis of resorcin[4]arene-based glycoclusters as multivalent ligands of lectins

Synthetic multivalent glycoclusters show promise as anti-adhesives for the treatment of bacterial infections. Here we report the synthesis of a family of tetravalent galactose and lactose functionalised macrocycles based on the resorcin[4]arene core. The development of diastereoselective synthetic routes for the formation of lower-rim propargylated resorcin[4]arenes and their functionalistion via Cu-catalyzed azide-alkyne click chemistry is described. ELLA binding studies confirm that galactose sugar clusters are effective ligands for the PA-IL bacterial lectin of Pseudomonas aeruginosa while poor binding for the lactose-based monovalent probe and no binding could be measured for the multivalent glycoclusters was observed for the human galectin-1.

Crystallization and preliminary X-ray crystallographic analysis of zebrafish prototype galectin Drgal1-L2

Zebrafish (Danio rerio) are an important developmental and embryological model given the optical clarity of the embryos and larvae, which permits real-time viewing of developing pathologies. More recently, a broader scope for these vertebrates to model a range of human diseases, including some cancers, has been indicated. Zebrafish Drgal1-L2 has been identified as an orthologue of mammalian galectin-1, which is is a carbohydrate-binding protein that exhibits β-galactoside-binding specificity and which is overexpressed by many aggressive human cancers. This study describes the cloning, expression in Escherichia coli, purification and crystallization of recombinant Drgal1-L2 protein in the presence of lactose (ligand). X-ray diffraction data from these novel crystals of zebrafish Drgal1-L2 were collected to a resolution of 1.5 Å using a synchrotron-radiation source, enabling their characterization.

Galectin inhibitory disaccharides promote tumour immunity in a breast cancer model

High level galectin-1 expression results in cancer cell evasion of the immune response, increased tumour survival and aggressive metastases. Using a galectin-1 polyclonal antibody, high levels of galectin-1 protein were shown to be expressed by breast cancer cells established from FVB/N MMTV-c-neu mice as well as by the B16F10 melanoma cell line. In mixed lymphocyte cultures using tumour cells as antigenic stimulators, addition of recombinant galectin-1 dose-dependently inhibited lymphocyte production. Disaccharides were identified that inhibited galectin-1 function and increased growth and activation of CD8(+) CTL's killing cancer cells. X-ray crystallographic structures of human galectin-1 in complex with inhibitory disaccharides revealed their mode of binding. Combining galectin-blocking carbohydrates as adjuvants with vaccine immunotherapy in vivo to promote immune responses significantly decreased tumour progression and improved the outcomes for tumour challenged mice. This is the first report showing that suitably selected galectin-1 blocking disaccharides will act as adjuvants promoting vaccine stimulated immune responses against tumours in vivo.

Disease-associated carbohydrate-recognising proteins and structure-based inhibitor design

The role of carbohydrate-related pathways in a wide range of clinically significant diseases has provided great impetus for researchers to characterise key proteins as targets for drug discovery. Carbohydrate-recognising proteins essential in the lifecycles of high health impact pathogens and diseases such as diabetes, cancer, autoimmunity, inflammation and in-born errors of metabolism continue to stimulate much interest in both structure elucidation and structure-based drug design. For example, advances in structure-based inhibitor design against the mycobacterial enzyme UDP-galactopyranose mutase offer new hope in next generation anti-tuberculosis chemotherapeutics. The appearance of H5N1 avian influenza virus has re-stimulated much research on influenza virus haemagglutinin and sialidase. These latest developments on influenza virus sialidase have provided new opportunity for the development of Group 1-specific anti-influenza drugs. The role of siglecs and galectins in a range of disease processes such as inflammation, apoptosis and cancer progression has also inspired significant structure-based inhibitor design research.