Glycosyldisulfides from dynamic combinatorial libraries as O-glycoside mimetics for plant and endogenous lectins: Their reactivities in solid-phase and cell assays and conformational analysis by molecular dynamics simulations

Selection of Galectin-Binding Ligands from Synthetic Glycopeptide Libraries

Galectins, a class of carbohydrate-binding proteins, play a crucial role in various physiological and disease processes. Therefore, the identification of ligands that efficiently bind these proteins could potentially lead to the development of new therapeutic compounds. In this study, we present a method that involves screening synthetic click glycopeptide libraries to identify lectin-binding ligands with low micromolar affinity. Our methodology, initially optimized using Concanavalin A, was subsequently applied to identify binders for the therapeutically relevant galectin 1. Binding affinities were assessed using various methods and showed that the selected glycopeptides exhibited enhanced binding potency to the target lectins compared to the starting sugar moieties. This approach offers an alternative means of discovering galectin-binding ligands as well as other carbohydrate-binding proteins, which are considered important therapeutic targets.

The ligand-dependent suppression of TCR signaling by the immune checkpoint receptor LAG3 depends on the cytoplasmic RRFSALE motif

Lymphocyte activation gene 3 (LAG3) is an inhibitory immune checkpoint receptor that restrains autoimmune and antitumor responses, but its evolutionarily conserved cytoplasmic tail lacks classical inhibitory motifs. Major histocompatibility complex class II (MHC class II) is an established LAG3 ligand, and fibrinogen-like protein 1 (FGL1), lymph node sinusoidal endothelial cell C-type lectin (LSECtin), and Galectin-3 have been proposed as alternative binding partners that play important roles in LAG3 function. Here, we used a fluorescent human T cell reporter system to study the function of LAG3. We found that LAG3 reduced the response to T cell receptor stimulation in the presence of MHC class II molecules to a lesser extent compared with the receptor programmed cell death protein 1. Analysis of deletion mutants demonstrated that the RRFSALE motif in the cytoplasmic tail of LAG3 was necessary and sufficient for LAG3-mediated inhibition. In this system, FGL1, but not LSECtin or Galectin-3, acted as a LAG3 ligand that weakly induced inhibition. LAG3-blocking antibodies attenuated LAG3-mediated inhibition in our reporter cells and enhanced reporter cell activation even in the absence of LAG3 ligands, indicating that they could potentially enhance T cell responses independently of their blocking effect.

Chemoselective Solution- and Solid-Phase Synthesis of Disulfide-Linked Glycopeptides

Glycosylation of peptides and proteins is a widely employed strategy to mimic important post-translational modifications or to modulate the physicochemical properties of peptides to enhance their delivery. Furthermore, glycosylation via a sulfur atom imparts increased chemical and metabolic stability to the resulting glycoconjugates. Herein, we report a simple and chemoselective procedure to prepare disulfide-linked glycopeptides. Acetate-protected glycosylsulfenyl hydrazines are shown to be highly reactive with the thiol group of cysteine residues within peptides, both in solution and as part of conventional solid-phase peptide synthesis protocols. The efficiency of this glycosylation methodology with unprotected carbohydrates is also demonstrated, which avoids the need for deprotection steps and further extends its utility, with disulfide-linked glycopeptides produced in excellent yields. Given the importance of glycosylated peptides in structural glycobiology, pharmacology, and therapeutics, the methodology outlined provides easy access to disulfide-linked glycopeptides as molecules with multiple biological applications.

Galectin-1 Cooperates with Yersinia Outer Protein (Yop) P to Thwart Protective Immunity by Repressing Nitric Oxide Production

Yersinia enterocolitica (Ye) inserts outer proteins (Yops) into cytoplasm to infect host cells. However, in spite of considerable progress, the mechanisms implicated in this process, including the association of Yops with host proteins, remain unclear. Here, we evaluated the functional role of Galectin-1 (Gal1), an endogenous β-galactoside-binding protein, in modulating Yop interactions with host cells. Our results showed that Gal1 binds to Yops in a carbohydrate-dependent manner. Interestingly, Gal1 binding to Yops protects these virulence factors from trypsin digestion. Given that early control of Ye infection involves activation of macrophages, we evaluated the role of Gal1 and YopP in the modulation of macrophage function. Although Gal1 and YopP did not influence production of superoxide anion and/or TNF by Ye-infected macrophages, they coordinately inhibited nitric oxide (NO) production. Notably, recombinant Gal1 (rGal1) did not rescue NO increase observed in Lgals1-/- macrophages infected with the YopP mutant Ye ∆yopP. Whereas NO induced apoptosis in macrophages, no significant differences in cell death were detected between Gal1-deficient macrophages infected with Ye ∆yopP, and WT macrophages infected with Ye wt. Strikingly, increased NO production was found in WT macrophages treated with MAPK inhibitors and infected with Ye wt. Finally, rGal1 administration did not reverse the protective effect in Peyer Patches (PPs) of Lgals1-/- mice infected with Ye ∆yopP. Our study reveals a cooperative role of YopP and endogenous Gal1 during Ye infection.

QSAR study of unsymmetrical aromatic disulfides as potent avian SARS-CoV main protease inhibitors using quantum chemical descriptors and statistical methods

In silico research was executed on forty unsymmetrical aromatic disulfide derivatives as inhibitors of the SARS Coronavirus (SARS-CoV-1). Density functional theory (DFT) calculation with B3LYP functional employing 6-311 ​+ ​G(d,p) basis set was used to calculate quantum chemical descriptors. Topological, physicochemical and thermodynamic parameters were calculated using ChemOffice software. The dataset was divided randomly into training and test sets consisting of 32 and 8 compounds, respectively. In attempt to explore the structural requirements for bioactives molecules with significant anti-SARS-CoV activity, we have built valid and robust statistics models using QSAR approach. Hundred linear pentavariate and quadrivariate models were established by changing training set compounds and further applied in test set to calculate predicted IC₅₀ values of compounds. Both built models were individually validated internally as well as externally along with Y-Randomization according to the OECD principles for the validation of QSAR model and the model acceptance criteria of Golbraikh and Tropsha's. Model 34 is chosen with higher values of R², R² _test and Q²cv (R² ​= ​0.838, R² _test ​= ​0.735, Q² _cv ​= ​0.757). It is very important to notice that anti-SARS-CoV main protease of these compounds appear to be mainly governed by five descriptors, i.e. highest occupied molecular orbital energy (E_HOMO), energy of molecular orbital below HOMO energy (E_HOMO-1), Balaban index (BI), bond length between the two sulfur atoms (S1S2) and bond length between sulfur atom and benzene ring (S2Bnz). Here the possible action mechanism of these compounds was analyzed and discussed, in particular, important structural requirements for great SARS-CoV main protease inhibitor will be by substituting disulfides with smaller size electron withdrawing groups. Based on the best proposed QSAR model, some new compounds with higher SARS-CoV inhibitors activities have been designed. Further, in silico prediction studies on ADMET pharmacokinetics properties were conducted.

On-water synthesis of glycosyl selenocyanate derivatives and their application in the metal free organocatalytic preparation of nonglycosidic selenium linked pseudodisaccharide derivatives

Glycosyl selenocyanate derivatives were prepared in very good yield by the treatment of glycosyl halide or triflate derivatives with potassium selenocyanate in water. A variety of selenium linked pseudodisaccharide derivatives were prepared in excellent yield using glycosyl selenocyanates as stable building blocks in the presence of hydrazine hydrate under metal-free organocatalytic reaction conditions.

Glycosyl disulfides: importance, synthesis and application to chemical and biological systems

This review explores methodologies for the preparation of glycosyl disulfides, their utility as intermediates in carbohydrate synthesis, and evaluates their biological impact in glycoscience and beyond.

Galectin-Glycan Interactions: Guidelines for Monitoring by 77 Se NMR Spectroscopy, and Solvent (H2 O/D2 O) Impact on Binding

Functional pairing between cellular glycoconjugates and tissue lectins like galectins has wide (patho)physiological significance. Their study is facilitated by nonhydrolysable derivatives of the natural O‐glycans, such as S‐ and Se‐glycosides. The latter enable extensive analyses by specific ⁷⁷Se NMR spectroscopy, but still remain underexplored. By using the example of selenodigalactoside (SeDG) and the human galectin‐1 and ‐3, we have evaluated diverse ⁷⁷Se NMR detection methods and propose selective ¹H,⁷⁷Se heteronuclear Hartmann–Hahn transfer for efficient use in competitive NMR screening against a selenoglycoside spy ligand. By fluorescence anisotropy, circular dichroism, and isothermal titration calorimetry (ITC), we show that the affinity and thermodynamics of SeDG binding by galectins are similar to thiodigalactoside (TDG) and N‐acetyllactosamine (LacNAc), confirming that Se substitution has no major impact. ITC data in D₂O versus H₂O are similar for TDG and LacNAc binding by both galectins, but a solvent effect, indicating solvent rearrangement at the binding site, is hinted at for SeDG and clearly observed for LacNAc dimers with extended chain length.

Stereoselective Synthesis of Carbon-Sulfur-Bridged Glycomimetics by Photoinitiated Thiol-Ene Coupling Reactions

Oligosaccharides and glycoconjugates are abundant in all living organisms, taking part in a multitude of biological processes. The application of natural O-glycosides in biological studies and drug development is limited by their sensitivity to enzymatic hydrolysis. This issue made it necessary to design hydrolytically stable carbohydrate mimetics, where sulfur, carbon, or longer interglycosidic connections comprising two or three atoms replace the glycosidic oxygen. However, the formation of the interglycosidic linkages between the sugar residues in high diastereoslectivity poses a major challenge. Here, we report on stereoselective synthesis of carbon-sulfur-bridged disaccharide mimetics by the free radical addition of carbohydrate thiols onto the exo-cyclic double bond of unsaturated sugars. A systematic study on UV-light initiated radical mediated hydrothiolation reactions of enoses bearing an exocyclic double bond at C1, C2, C3, C4, C5, and C6 positions of the pyranosyl ring with various sugar thiols was performed. The effect of temperature and structural variations of the alkenes and thiols on the efficacy and stereoselectivity of the reactions was systematically studied and optimized. The reactions proceeded with high efficacy and, in most cases, with complete diastereoselectivity producing a broad array of disaccharide mimetics coupling through an equatorially oriented methylensulfide bridge.

Selenoglycosides as Lectin Ligands: 77 Se-Edited CPMG-HSQMBC NMR Spectroscopy To Monitor Biomedically Relevant Interactions

The fundamental importance of protein-glycan recognition calls for specific and sensitive high-resolution techniques for their detailed analysis. After the introduction of 19 F NMR spectroscopy to study the recognition of fluorinated glycans, a new 77 Se NMR spectroscopy method is presented for complementary studies of selenoglycans with optimised resolution and sensitivity, in which direct NMR spectroscopy detection on 77 Se is replaced by its indirect observation in a 2D 1 H,77 Se HSQMBC spectrum. In contrast to OH/F substitution, O/Se exchange allows the glycosidic bond to be targeted. As an example, selenodigalactoside recognition by three human galectins and a plant toxin is readily indicated by signal attenuation and line broadening in the 2D 1 H,77 Se HSQMBC spectrum, in which CPMG-INEPT long-range transfer ensures maximal detection sensitivity, clean signal phases, and reliable ligand ranking. By monitoring competitive displacement of a selenated spy ligand, the selective 77 Se NMR spectroscopy approach may also be used to screen non-selenated compounds. Finally, 1 H,77 Se CPMG-INEPT transfer allows further NMR sensors of molecular interaction to be combined with the specificity and resolution of 77 Se NMR spectroscopy.

Bivalent glycoconjugates based on 1,5-diazabicyclo[3.3.0]octa-3,6-diene-2,8-dione ("bimane") as a central scaffold

The heteroaromatic fused diazabicyclic "bimane" ring system, discovered four decades ago, is endowed with remarkable chemical and photophysical properties. No carbohydrate derivatives of bimanes have, however, been described thus far. Here we report on the syntheses of a range of bimanes decorated with various glycosyl residues. Mono- and disaccharide residues were attached to syn- or anti-bimane central cores via thio-, disulfido- or selenoglycosidic linkages to obtain novel fluorescent or nonfluorescent glycoconjugates. Cu(I)-catalyzed cycloaddition of glycosyl azides to a bimane diethynyl derivative furnished further bivalent glycoconjugates with sugar residues linked to the central bimane core via 1,2,3-triazole rings. We have determined the crystal and molecular structures of several glycosylated and non-glycosylated bimanes and report fluorescence data for the new compounds.

Straightforward S-S Bond Formation via the Oxidation of S-Acetyl by Iodine in the Presence of N-Iodosuccinimide

Straightforward S-S bond formation via the oxidation of S-acetyl group by iodine was reported here. The reaction was further applied in the synthesis of per-O-acetylated glycosyl disulfides. These studies demonstrated great improvement in reaction rate, yield, and general convenience in the presence of N-iodosuccinimide. Furthermore, selectively deacetylated glycosyl thiols were obtained in high yields when these per-O-acetylated glycosyl disulfides were reduced with tris(2-carboxyethyl)-phosphine (TCEP). Our method supplied an efficient way to obtain both per-O-acetylated glycosyl disulfides and per-O-acetylated glycosyl thiols in which the sulfur group was located at any position.

Diglycosyl diselenides alter redox homeostasis and glucose consumption of infective African trypanosomes

With the aim to develop compounds able to target multiple metabolic pathways and, thus, to lower the chances of drug resistance, we investigated the anti-trypanosomal activity and selectivity of a series of symmetric diglycosyl diselenides and disulfides. Of 18 compounds tested the fully acetylated forms of di-β-D-glucopyranosyl and di-β-D-galactopyranosyl diselenides (13 and 15, respectively) displayed strong growth inhibition against the bloodstream stage of African trypanosomes (EC₅₀ 0.54 μM for 13 and 1.49 μM for 15) although with rather low selectivity (SI < 10 assayed with murine macrophages). Nonacetylated versions of the same sugar diselenides proved to be, however, much less efficient or completely inactive to suppress trypanosome growth. Significantly, the galactosyl (15), and to a minor extent the glucosyl (13), derivative inhibited glucose catabolism but not its uptake. Both compounds induced redox unbalance in the pathogen. In vitro NMR analysis indicated that diglycosyl diselenides react with glutathione, under physiological conditions, via formation of selenenylsulfide bonds. Our results suggest that non-specific cellular targets as well as actors of the glucose and the redox metabolism of the parasite may be affected. These molecules are therefore promising leads for the development of novel multitarget antitrypanosomal agents.

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Acetylated diglycosyl diselenides inhibit the proliferation of infective Trypanosoma brucei.

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A galactosyl derivative impairs parasite' glucose consumption and redox homeostasis.

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Diglycosyl diselenides react covalently with glutathione under mild conditions..

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Acetylated diglycosyl diselenides represent multitarget antitrypanosomal candidates.

Protein-Directed Dynamic Combinatorial Chemistry: A Guide to Protein Ligand and Inhibitor Discovery

Protein-directed dynamic combinatorial chemistry is an emerging technique for efficient discovery of novel chemical structures for binding to a target protein. Typically, this method relies on a library of small molecules that react reversibly with each other to generate a combinatorial library. The components in the combinatorial library are at equilibrium with each other under thermodynamic control. When a protein is added to the equilibrium mixture, and if the protein interacts with any components of the combinatorial library, the position of the equilibrium will shift and those components that interact with the protein will be amplified, which can then be identified by a suitable biophysical technique. Such information is useful as a starting point to guide further organic synthesis of novel protein ligands and enzyme inhibitors. This review uses literature examples to discuss the practicalities of applying this method to inhibitor discovery, in particular, the set-up of the combinatorial library, the reversible reactions that may be employed, and the choice of detection methods to screen protein ligands from a mixture of reversibly forming molecules.

Novel strategies for the synthesis of unsymmetrical glycosyl disulfides

Novel strategies for the efficient synthesis of unsymmetrical glycosyl disulfides are reported. Glycosyl disulfides are increasingly important as glycomimetics and molecular probes in glycobiology. Sialosyl disulfides are synthesised directly from the chlorosialoside Neu5Ac2Cl, proceeding via a thiol-disulfide exchange reaction between the sialosyl thiolate and symmetrical disulfides. This methodology was adapted and found to be successfully applicable to the synthesis of unsymmetrical glucosyl disulfides under mild conditions.

Glycosyldiselenides as lectin ligands detectable by NMR in biofluids

The ability of glycosyldiselenides to act as lectin ligands and their selective detection in plasma by (77)Se NMR is reported.

Synthesis of mixed glycosyl disulfides/selenenylsulfides using benzyltriethylammonium tetrathiomolybdate as a sulfur transfer reagent

An easy and mild method has been developed for the synthesis of mixed glycosyl disulfides/selenenylsulfides from glycosyl halides and diaryl/dialkyl dichalcogenides in the presence of benzyltriethylammonium tetrathiomolybdate [(BnEt3N)2MoS4]. The salient feature of this method is the sulfur transfer from [BnEt3N]2MoS4 to form glycosyl disulfides which with excess tetrathiomolybdate further undergo exchange reaction with other dichalcogenides in a one-pot operation.

Thio- and selenoglycosides as ligands for biomedically relevant lectins: valency-activity correlations for benzene-based dithiogalactoside clusters and first assessment for (di)selenodigalactosides

Substitution of the oxygen atom in the glycosidic linkage by a disulfide bond or by selenium makes the resulting glycoside resistant to hydrolysis. To clarify the consequences for affinity to lectins we prepared benzene-based mono- to trivalent dithiogalactosides. Inhibitory capacity increased with valency for a plant toxin, the synthetic compounds potently blocking its binding to a lactose-presenting matrix and to cells. Human galectins were much less sensitive to the disulfides than the toxin. This differential response constitutes a beneficial effect to avoid cross-reactivity in vivo. Symmetrical selenodigalactoside and diselenodigalactoside were prepared and similarly tested. Both compounds proved rather equally bioactive for the toxin, graded activity was measured for human galectins. This result directs attention to further studies to relate Se-dependent alterations in bond angle and length as well as van der Waals radius to binding properties of selenoglycosides to biomedically relevant lectins.

Dynamic combinatorial/covalent chemistry: a tool to read, generate and modulate the bioactivity of compounds and compound mixtures

Reversible covalent bond formation under thermodynamic control adds reactivity to self-assembled supramolecular systems, and is therefore an ideal tool to assess complexity of chemical and biological systems. Dynamic combinatorial/covalent chemistry (DCC) has been used to read structural information by selectively assembling receptors with the optimum molecular fit around a given template from a mixture of reversibly reacting building blocks. This technique allows access to efficient sensing devices and the generation of new biomolecules, such as small molecule receptor binders for drug discovery, but also larger biomimetic polymers and macromolecules with particular three-dimensional structural architectures. Adding a kinetic factor to a thermodynamically controlled equilibrium results in dynamic resolution and in self-sorting and self-replicating systems, all of which are of major importance in biological systems. Furthermore, the temporary modification of bioactive compounds by reversible combinatorial/covalent derivatisation allows control of their release and facilitates their transport across amphiphilic self-assembled systems such as artificial membranes or cell walls. The goal of this review is to give a conceptual overview of how the impact of DCC on supramolecular assemblies at different levels can allow us to understand, predict and modulate the complexity of biological systems.

Routine Microsecond Molecular Dynamics Simulations with AMBER on GPUs. 2. Explicit Solvent Particle Mesh Ewald

We present an implementation of explicit solvent all atom classical molecular dynamics (MD) within the AMBER program package that runs entirely on CUDA-enabled GPUs. First released publicly in April 2010 as part of version 11 of the AMBER MD package and further improved and optimized over the last two years, this implementation supports the three most widely used statistical mechanical ensembles (NVE, NVT, and NPT), uses particle mesh Ewald (PME) for the long-range electrostatics, and runs entirely on CUDA-enabled NVIDIA graphics processing units (GPUs), providing results that are statistically indistinguishable from the traditional CPU version of the software and with performance that exceeds that achievable by the CPU version of AMBER software running on all conventional CPU-based clusters and supercomputers. We briefly discuss three different precision models developed specifically for this work (SPDP, SPFP, and DPDP) and highlight the technical details of the approach as it extends beyond previously reported work [Götz et al., J. Chem. Theory Comput. 2012, DOI: 10.1021/ct200909j; Le Grand et al., Comp. Phys. Comm. 2013, DOI: 10.1016/j.cpc.2012.09.022].We highlight the substantial improvements in performance that are seen over traditional CPU-only machines and provide validation of our implementation and precision models. We also provide evidence supporting our decision to deprecate the previously described fully single precision (SPSP) model from the latest release of the AMBER software package.

Stereocontrolled 1-S-glycosylation and comparative binding studies of photoprobe-thiosaccharide conjugates with their O-linked analogs

The use of thioglycosides and other glycan derivatives with anomeric sulfur linkages is gaining increasing interest, both in synthesis and in various biological contexts. Herein, we demonstrate the occurrence and circumvention of anomerization during 1-S-glycosylation reactions, and present highly efficient and stereocontrolled syntheses of a series of photoprobe-thiosaccharide conjugates. Mutarotation of glycosyl thiols proved to be the origin of the anomeric mixtures formed, and kinetic effects could be used to circumvent anomerization. The synthesized carbohydrate conjugates were then evaluated by both solution- and solid-phase-based techniques. Both binding results showed that the S-linked glyco-sides interact with their cognate lectins comparably to the corresponding O-analogs in the present cases, thus demonstrating the reliability of the solid-support platform built upon our photo-initiated carbohydrate immobilization method for probing protein bindings, and showing the potential of combining these two means for studying carbohydrate-protein interactions.

Galectin-3 binds Neisseria meningitidis and increases interaction with phagocytic cells

Galectin-3 is expressed and secreted by immune cells and has been implicated in multiple aspects of the inflammatory response. It is a glycan binding protein which can exert its functions within cells or exogenously by binding cell surface ligands, acting as a molecular bridge or activating signalling pathways. In addition, this lectin has been shown to bind to microorganisms. In this study we investigated the interaction between galectin-3 and Neisseria meningitidis, an important extracellular human pathogen, which is a leading cause of septicaemia and meningitis. Immunohistochemical analysis indicated that galectin-3 is expressed during meningococcal disease and colocalizes with bacterial colonies in infected tissues from patients. We show that galectin-3 binds to N. meningitidis and we demonstrate that this interaction requiresfull-length, intact lipopolysaccharide molecules. We found that neither exogenous nor endogenous galectin-3 contributes to phagocytosis of N. meningitidis; instead exogenous galectin-3 increases adhesion to monocytes and macrophages but not epithelial cells. Finally we used galectin-3 deficient (Gal-3(-/-) ) mice to evaluate the contribution of galectin-3 to meningococcal bacteraemia. We found that Gal-3(-/-) mice had significantly lower levels of bacteraemia compared with wild-type mice after challenge with live bacteria, indicating that galectin-3 confers an advantage to N. meningitidis during systemic infection.

Non-synonymous single nucleotide polymorphisms in genes for immunoregulatory galectins: association of galectin-8 (F19Y) occurrence with autoimmune diseases in a Caucasian population

BACKGROUND

Galectins are potent immune regulators, with galectin-8 acting as a pro-apoptotic effector on synovial fluid cells and thymocytes and stimulator on T-cells. To set a proof-of-principle example for risk assessment in autoimmunity, and for a mutation affecting physiological galectin sensor functions, a polymorphism in the coding region of the galectin-8 gene (rs2737713; F19Y) was studied for its association with two autoimmune disorders, i.e. rheumatoid arthritis and myasthenia gravis.

METHODS

A case-control analysis and a related quantitative trait-association study were performed to investigate the association of this polymorphism in patients (myasthenia gravis 149, rheumatoid arthritis 214 and 134 as primary and repetitive cohorts, respectively) and 365 ethnically matched (Caucasian) healthy controls. Distribution was also investigated in patients grouped according to their antibody status and age at disease onset. Comparative testing for lectin activity was carried out in ELISA/ELLA-based binding tests with both wild-type and F19Y mutant galectin-8 from peripheral blood mononuclear cell lysates of healthy individuals with different genotypes as well as with recombinant wild-type and F19Y mutant galectin-8 proteins.

RESULTS

A strong association was found for rheumatoid arthritis, and a mild one with myasthenia gravis. Furthermore, the presence of the sequence deviation also correlated with age at disease onset in the case of rheumatoid arthritis. The F19Y substitution did not appear to affect carbohydrate binding in solid-phase assays markedly.

GENERAL SIGNIFICANCE

This is the first report of an association between a galectin-based polymorphism leading to a mutant protein and autoimmune diseases, with evidence for antagonistic pleiotropy.

Adhesion/growth-regulatory galectins in the human eye: localization profiles and tissue reactivities as a standard to detect disease-associated alterations

OBJECTIVES

To characterize the localization profiles of seven adhesion/growth-regulatory galectins in the normal human eye using immunodetection of endogenous galectins and binding of labeled galectins to sections, useful as a basis to detect disease-associated alterations.

METHODS

Non-cross-reactive anti-galectin antibodies and biotinylated galectins were tested on acetone-fixed cryosections of normal human donor eyes. Controls included omission of first-step reagent, testing of an antibody against a galectin specific for rat (galectin-5), and blocking of galectin binding with lactose.

RESULTS

Galectin presence was not restricted to one or few members of this family. Signal occurrence can even include all tested or most proteins (conjunctival or corneal epithelium), whereas choroid positivity is fully accounted for by galectin-9. Regional specificity and characteristic profiles for each protein, immuno- and galectin histochemically, were determined. Differences in tissue reactivity among the galectins were detected.

CONCLUSIONS

That the galectins have characteristic localization/reactivity profiles supports the concept of a network with potential for non-overlapping functions. The reported data thus prompt to proceed to the respective analysis of specimens from ocular diseases.

Galectins promote the interaction of influenza virus with its target cell

Influenza virus is known to bind sialoglycans located on the surface of the host cell. In addition, recent data suggest the involvement of other molecular targets in viral reception. Of note, a high density of terminal galactose residues is created on the surface of virions because of the influenza virus' own neuraminidase activity. Thus, we suggested the possibility for an interaction of the influenza virus with galactose-binding proteins--galectins. In the present work we studied the influence of several galectins on the adhesion and further internalization of virus into the cell; six virus strains and three cell lines were studied. Chicken galectins CG-1A and -2 as well as human galectins HGal-1 and -8 promote virus binding in dose dependent manner, but they do not influence the internalization stage. Also, galectins are able to restore the ability of influenza virus to infect desialylated cells up to the level of native cells. When CG-1A in physiological concentrations was loaded onto viruses, the adhesion level was higher than in the case of on-cell loading. The effect of adhesion increase depends on the glycan structure of target-cell as well as of virus. The aggregated data suggest a promotional effect of galectins during the stage of influenza virus binding with the surface of target-cell.

Structural aspects of binding of α-linked digalactosides to human galectin-1

By definition, adhesion/growth-regulatory galectins are known for their ability to bind β-galactosides such as Galβ(1 → 4)Glc (lactose). Indications for affinity of human galectin-1 to α-linked digalactosides pose questions on the interaction profile with such bound ligands and selection of the galactose moiety for CH-π stacking. These issues are resolved by a combination of (15)N-(1)H heteronuclear single quantum coherence (HSQC) chemical shift and saturation transfer difference nuclear magnetic resonance (STD NMR) epitope mappings with docking analysis, using the α(1 → 3/4)-linked digalactosides and also Galα(1 → 6)Glc (melibiose) as test compounds. The experimental part revealed interaction with the canonical lectin site, and this preferentially via the non-reducing-end galactose moiety. Low-energy conformers appear to be selected without notable distortion, as shown by molecular dynamics simulations. With the α(1 → 4) disaccharide, however, the typical CH-π interaction is significantly diminished, yet binding appears to be partially compensated for by hydrogen bonding. Overall, these findings reveal that the type of α-linkage in digalactosides has an impact on maintaining CH-π interactions and the pattern of hydrogen bonding, explaining preference for the α(1 → 3) linkage. Thus, this lectin is able to accommodate both α- and β-linked galactosides at the same site, with major contacts to the non-reducing-end sugar unit.

Symmetric dithiodigalactoside: strategic combination of binding studies and detection of selectivity between a plant toxin and human lectins

Thioglycosides offer the advantage over O-glycosides to be resistant to hydrolysis. Based on initial evidence of this recognition ability for glycosyldisulfides by screening dynamic combinatorial libraries, we have now systematically studied dithiodigalactoside on a plant toxin (Viscum album agglutinin) and five human lectins (adhesion/growth-regulatory galectins with medical relevance e.g. in tumor progression and spread). Inhibition assays with surface-presented neoglycoprotein and in solution monitored by saturation transfer difference NMR spectroscopy, flanked by epitope mapping, as well as isothermal titration calorimetry revealed binding properties to VAA (K(a): 1560 ± 20 M(-1)). They were reflected by the structural model and the affinity on the level of toxin-exposed cells. In comparison, galectins were considerably less reactive, with intrafamily grading down to very minor reactivity for tandem-repeat-type galectins, as quantitated by radioassays for both domains of galectin-4. Model building indicated contact formation to be restricted to only one galactose moiety, in contrast to thiodigalactoside. The tested glycosyldisulfide exhibits selectivity between the plant toxin and the tested human lectins, and also between these proteins. Therefore, glycosyldisulfides have potential as chemical platform for inhibitor design.

Galectins as tools for glycan mapping in histology: comparison of their binding profiles to the bovine zona pellucida by confocal laser scanning microscopy

Gene divergence has given rise to the galectin family of mammalian lectins. Since selective binding to distinct β-galactosides underlies the known bioactivities of galectins, they could find application in cyto- and histochemistry. The pertinent question on the characteristics of their individual reactivity profiles therefore needs to be answered. Toward this end, comparative studies of a panel of galectins in defined systems are required. We here characterise the staining profiles of seven human lectins as well as five natural derivatives originating from proteolytic truncation and serine phosphorylation and one engineered variant. As test system, bovine germinal vesicle oocytes with their glycoprotein envelope (zona pellucida), which presents bi- to tetraantennary complex-type N-glycans with N-acetyllactosamine repeats and core fucosylation, were processed. Technically, confocal laser scanning microscopy was used, first with plant lectins to map the sialylation status. Hereby, α2,3/6-sialylation was detected in the superficial filamentous meshwork of the zona pellucida, while sialic acid-free glycan chains were found to characterise the main inner part of the compact layer of the zona pellucida. Galectin staining was specific and non-uniform. Significant differences in reactivity were detected for the superficial filamentous meshwork and the compact layer of the zona pellucida between galectins-1 to -4 versus galectins-8 and -9. The typical staining profiles intimate a spatially organised display of N-glycans in the different layers of the zona pellucida, underscoring the potential of galectins as cyto- and histochemical tools. Our results encourage further comparative analysis and research to trace the underlying structural and/or topological properties.

Human galectins induce conversion of dermal fibroblasts into myofibroblasts and production of extracellular matrix: potential application in tissue engineering and wound repair

Members of the galectin family of endogenous lectins are potent adhesion/growth-regulatory effectors. Their multifunctionality opens possibilities for their use in bioapplications. We studied whether human galectins induce the conversion of human dermal fibroblasts into myofibroblasts (MFBs) and the production of a bioactive extracellular matrix scaffold is suitable for cell culture. Testing a panel of galectins of all three subgroups, including natural and engineered variants, we detected activity for the proto-type galectin-1 and galectin-7, the chimera-type galectin-3 and the tandem-repeat-type galectin-4. The activity of galectin-1 required the integrity of the carbohydrate recognition domain. It was independent of the presence of TGF-β1, but it yielded an additive effect. The resulting MFBs, relevant, for example, for tumor progression, generated a matrix scaffold rich in fibronectin and galectin-1 that supported keratinocyte culture without feeder cells. Of note, keratinocytes cultured on this substratum presented a stem-like cell phenotype with small size and keratin-19 expression. In vivo in rats, galectin-1 had a positive effect on skin wound closure 21 days after surgery. In conclusion, we describe the differential potential of certain human galectins to induce the conversion of dermal fibroblasts into MFBs and the generation of a bioactive cell culture substratum.