[Show abstract][Hide abstract] ABSTRACT: Osteoarthritis is a degenerative joint disease that ranks among the leading causes of adult disability. Mechanisms underlying osteoarthritis pathogenesis are not yet fully elucidated, putting limits to current disease management and treatment. Based on the phenomenological evidence for dysregulation within the glycome of chondrocytes and the network of a family of adhesion/growth-regulatory lectins, that is, galectins, we tested the hypothesis that Galectin-1 is relevant for causing degeneration. Immunohistochemical analysis substantiated that Galectin-1 upregulation is associated with osteoarthritic cartilage and subchondral bone histopathology and severity of degeneration (p < 0.0001, n = 29 patients). In vitro, the lectin was secreted and it bound to osteoarthritic chondrocytes inhibitable by cognate sugar. Glycan-dependent Galectin-1 binding induced a set of disease markers, including matrix metalloproteinases and activated NF-κB, hereby switching on an inflammatory gene signature (p < 10(-16)). Inhibition of distinct components of the NF-κB pathway using dedicated inhibitors led to dose-dependent impairment of Galectin-1-mediated transcriptional activation. Enhanced secretion of effectors of degeneration such as three matrix metalloproteinases underscores the data's pathophysiological relevance. This study thus identifies Galectin-1 as a master regulator of clinically relevant inflammatory-response genes, working via NF-κB. Because inflammation is critical to cartilage degeneration in osteoarthritis, this report reveals an intimate relation of glycobiology to osteoarthritic cartilage degeneration.
No preview · Article · Jan 2016 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: A library of eight amphiphilic Janus glycodendrimers (GDs) with d-mannose (Man) headgroups, a known routing signal for lectin-mediated transport processes, was constructed via an iterative modular methodology. Sequence-defined variations of the Janus GD modulate the surface density and sequence of Man after self-assembly into multilamellar glycodendrimersomes (GDSs). The spatial mode of Man presentation is decisive for formation of either unilamellar or onion-like GDS vesicles. Man presentation and Janus GD concentration determine GDS size and number of bilayers. Beyond vesicle architecture, Man topological display affects kinetics and plateau level of GDS aggregation by a tetravalent model lectin: the leguminous agglutinin Con A, which is structurally related to endogenous cargo transporters. The agglutination process was rapid, efficient, and readily reversible for onion-like GDSs, demonstrating their value as versatile tools to explore the nature of physiologically relevant glycan/lectin pairing.
No preview · Article · Jan 2016 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: We report the sequential construction of a set of multivalent structures using cyclotriphosphazene (CTP) units, which were extensively used as primary or secondary cores implementing branching. The utilization of classical convergent and divergent approaches, together with accelerated dendritic strategies comprising orthogonal sequences, double-exponential and double-stage methodologies will be documented and discussed. Straightforward generation of non-conventional glycodendritic systems with surfaces rich in selectable headgroups, despite a low number of dendrimer generation, was achieved with the efficient assembly of highly functionalized AB3 and AB5 nanosynthons. The versatility of the methodology allowed access to a wide variety of structurally diversified platforms. The synthesis was completed by peripheral functionalization with spacered saccharides. The resulting architectures can be drawn as classical globular topologies, also dumbbell shapes and "onion peel" design, referred to as hypercores, wedged hypermonomers, glycoclusters, and glycodendrimers. The convenient implementation of controlled topological diversification is considered instrumental for providing sensitive and potent tools to delineate rules for structure-activity relationships in carbohydrate-protein (lectin) interactions, with possibility to tailor size, valency, ligand density, and topology. To illustrate the applicability of this approach for construction of biologically active glycoconjugates, competitive surface plasmon resonance studies were performed with a bacterial virulence factor and a human adhesion/growth-regulatory lectin and showed multivalent effects.
Full-text · Article · Nov 2015 · Polymer Chemistry
[Show abstract][Hide abstract] ABSTRACT: The characterization of the binding of reducing carbohydrates present as mixtures of anomers in solution to a sugar recepor (lectin) poses severe difficulties. In this situation, NMR spectroscopy enables the observation of signals for each anomer in the mixture by applying approaches based on ligand observation. Saturation transfer difference (STD) NMR allows fast and efficient screening of compound mixtures for reactivity to a receptor. Owing to the exceptionally favorable properties of (19)F in NMR spectroscopy and the often complex ¹H spectra of carbohydrates, (19)F-containing sugars have the potential to be turned into versatile sensors for recognition. Extending the recently established ¹H → ¹H STDre(19)F-NMR technique, we here demonstrate its applicability to measure anomeric selectivity of binding in a model system using the plant lectin concanavalin A (ConA) and 2-deoxy-2-fluoro-d-mannose. Indeed, it is also possible to account for the mutual inhibition between the anomers on binding to the lectin by means of a kinetic model. The monitoring of (19)F-NMR signal perturbation disclosed the relative activities of the anomers in solution and thus enabled the calculation of their binding affinity towards ConA. The obtained data show a preference for the α anomer that increases with temperature. This experimental approach can be extended to others systems of biomedical interest by testing human lectins with suitably tailored glycan derivatives.
[Show abstract][Hide abstract] ABSTRACT: Recognition of glycans by lectins leads to cell adhesion and growth regulation. The specificity and selectivity of this process are determined by carbohydrate structure (sequence and shape) and topology of its presentation. The synthesis of (neo)glycoconjugates with bi- to oligo-valency (glycoclusters) affords tools to delineate structure-activity relationships by blocking lectin binding to an artificial matrix, often a glycoprotein, or cultured cell lines. The drawback of these assays is that glycan presentation is different from that in tissues. In order to approach the natural context, we here introduce lectin histochemistry on fixed tissue sections to determine the susceptibility of binding of two plant lectins, i.e., GSA-II and WGA, to a series of 10 glycoclusters. Besides valency, this panel covers changes in the anomeric position (α/β) and the atom at the glycosidic linkage (O/S). Flanked by cell and solid-phase assays with human tumor lines and two mucins, respectively, staining (intensity and profile) was analyzed in sections of murine jejunum, stomach and epididymis as a function of glycocluster presence. The marked and differential sensitivity of signal generation to structural aspects of the glycoclusters proves the applicability of this method. This enables comparisons between data sets obtained by using (neo)glycoconjugates, cells and the tissue context as platforms. The special advantage of processing tissue sections is the monitoring of interference with lectin association at sites that are relevant for functionality. Testing glycoclusters in lectin histochemistry will especially be attractive in cases of multi-target recognition (glycans, proteins and lipids) by a tissue lectin.
[Show abstract][Hide abstract] ABSTRACT: Axon-like neuritogenesis in neuroblastoma (NG108-15) cells and primary cerebellar granular neurons is furthered by the presence of ganglioside GM1. We describe here that galectin-1 (Gal-1), a homobivalent endogenous lectin, is an effector by cross-linking the ganglioside and its associated glycoprotein α5 β1 -integrin. The thereby triggered signaling cascade involves autophosphorylation of focal adhesion kinase and activation of phospholipase Cγ and phosphoinositide-3 kinase. This leads to a transient increase in the intracellular Ca(2+) concentration by opening of TRPC5 channels, which belong to the signal transduction-gated cation channels. Controls with GM1-defective cells (NG-CR72, and neurons from ganglio-series KO mice) were retarded in axonal growth, underscoring the relevance of GM1 as functional counterreceptor for Gal-1. The lectin's presence was detected in the NG108-15 cells, suggesting an autocrine mechanism of action, and in astrocytes in situ. Gal-1, as cross-linking lectin, can thus translate metabolic conversion of ganglioside GD1a to GM1 by neuraminidase action into axon growth. This article is protected by copyright. All rights reserved.
No preview · Article · Nov 2015 · Journal of Neurochemistry
[Show abstract][Hide abstract] ABSTRACT: A key effector route of the Sugar Code involves lectins that exert crucial regulatory controls by targeting distinct cellular glycans. We demonstrate that a single amino-acid substitution in a banana lectin, replacing histidine 84 with a threonine, significantly reduces its mitogenicity, while preserving its broad-spectrum antiviral potency. X-ray crystallography, NMR spectroscopy, and glycocluster assays reveal that loss of mitogenicity is strongly correlated with loss of pi-pi stacking between aromatic amino acids H84 and Y83, which removes a wall separating two carbohydrate binding sites, thus diminishing multivalent interactions. On the other hand, monovalent interactions and antiviral activity are preserved by retaining other wild-type conformational features and possibly through unique contacts involving the T84 side chain. Through such fine-tuning, target selection and downstream effects of a lectin can be modulated so as to knock down one activity, while preserving another, thus providing tools for therapeutics and for understanding the Sugar Code.
[Show abstract][Hide abstract] ABSTRACT: Cycloadduct 1 is a conformationally constrained mimetic of the tumor-associated Tn antigen. It maintains the 4C1 conformation and the α-O-glycosidic linkage of the natural epitopes. Due to its tricyclic structure, the anomeric linkage is constrained and its conformation “frozen”. Using saturation transfer difference NMR spectroscopy experiments, epitope mapping for binding by three lectins [i.e., from Erythrina cristagalli (ECL), human macrophages (MGL), and from Helix pomatia (HPA)] was carried out. Striking differences in the epitope viewed from the ligand's perspective were revealed by this comparison. Evidently, the structural change around the C-2 position has a major impact, if the contact pattern to the ligand is not mostly restricted to galacto configuration with the axial hydroxyl group at C-4, in combination with C-3/C-6. These measurements thus provide insights into actual contacts, which help predict applicability as an inhibitor for distinct lectins, and as an elicitor of specific antibodies.
Full-text · Article · Sep 2015 · European Journal of Organic Chemistry
[Show abstract][Hide abstract] ABSTRACT: A library of eight amphiphilic Janus glycodendrimers (Janus-GDs) presenting D-lactose (Lac) and a combination of Lac with up to eight methoxytriethoxy (3EO) units in a sequence-defined arrangement was synthesized via an iterative modular methodology. The length of the linker between Lac and the hydrophobic part of the Janus-GDs was also varied. Self-assembly by injection from THF solution into phosphate-buffered saline (PBS) led to unilamellar, monodisperse glycodendrimersomes (GDSs) with dimensions predicted by Janus-GD concentration. These GDSs provided a toolbox to measure bioactivity profiles in agglutination assays with sugar binding proteins (lectins). Three naturally occurring forms of the human adhesion/growth-regulatory lectin galectin-8 (Gal-8S and Gal-8L), which differ by the length of linker connecting their two active domains, and a single-amino acid mutant (F19Y) were used as probes to study activity and sensor capacity. Unpredictably, the sequence of Lac on the Janus-GDs was demonstrated to determine bioactivity with the highest level revealed for a Janus-GD with six 3EO groups and one Lac. A further increase in Lac density was invariably accompanied by a substantial decrease in agglutination, whereas a decrease in Lac density resulted in similar or lower bioactivity and sensor capacity. Both changes in topology of Lac presentation of the GDSs and seemingly subtle alterations in protein structure resulted in different levels of bioactivity, demonstrating the presence of regulation on both GDS surface and lectin. These results illustrate the applicability of Janus-GDs to dissect structure-activity relationships between programmable cell surface models and human lectins in a highly sensitive and physiologically relevant manner.
No preview · Article · Sep 2015 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: Estrogen deprivation is considered responsible for many age-related processes, including poor wound healing. Guided by previous observations that estradiol accelerates re‑epithelialization through estrogen receptor (ER)‑β, in the present study, we examined whether selective ER agonists [4,4',4''-(4-propyl [1H] pyrazole-1,3,5-triyl)‑trisphenol (PPT), ER‑α agonist; 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN), ER‑β agonist] affect the expression of basic proliferation and differentiation markers (Ki‑67, keratin‑10, ‑14 and ‑19, galectin‑1 and Sox‑2) of keratinocytes using HaCaT cells. In parallel, ovariectomized rats were treated daily with an ER modulator, and wound tissue was removed 21 days after wounding and routinely processed for basic histological analysis. Our results revealed that the HaCaT keratinocytes expressed both ER‑α and ‑β, and thus are well-suited for studying the effects of ER agonists on epidermal regeneration. The activation of ER‑α produced a protein expression pattern similar to that observed in the control culture, with a moderate expression of Ki‑67 being observed. However, the activation of ER‑β led to an increase in cell proliferation and keratin‑19 expression, as well as a decrease in galectin‑1 expression. Fittingly, in rat wounds treated with the ER‑β agonist (DPN), epidermal regeneration was accelerated. In the present study, we provide information on the mechanisms through which estrogens affect the expression patterns of selected markers, thus modulating keratinocyte proliferation and differentiation; in addition, we demonstrate that the pharmacological activation of ER-α and -β has a direct impact on wound healing.
Preview · Article · Sep 2015 · International Journal of Molecular Medicine
[Show abstract][Hide abstract] ABSTRACT: To assess the impact of Acanthamoeba keratitis (AK) and amniotic membrane transplantation (AMT) in corneal explants on presence of two multifunctional endogenous lectins, i.e. galectins-1 and -7.
Ten corneal explants from AK patients (five with previous AMT and five controls without this treatment) and seven specimens of disease-free control cornea were processed by indirect fluorescent immunohistochemistry.
Immunostaining for both galectins was obtained in the epithelium, stroma and the endothelial layer of all controls, with the strongest positivity in the epithelium. Significantly decreased intensity for galectin-1 was recorded in the epithelium of corneal explants from patients with AK and AMT. The signal for galectin-7 was significantly decreased in the epithelium of AK patients and normalized after AMT.
AMT has a marked impact on presence of the two galectins in opposite directions, encouraging complete profiling for this family of endogenous effectors.
No preview · Article · Sep 2015 · Current eye research
[Show abstract][Hide abstract] ABSTRACT: A shift to short-chain glycans is an observed change in mucin-type O-glycosylation in pre- and malignant epithelia. Given the evidence that human galectin-3 can interact with mucins and also weakly with free tumor-associated Thomsen-Friedenreich (TF) tumor-associated antigen (CD176), the study of its interaction with MUC1 (glyco)peptides is of biomedical relevance. Glycosylated MUC1 fragments that carry the TF antigen attached either through Thr or Ser side chains were synthesized using standard Fmoc-based automated solid-phase peptide chemistry. The dissociation constants (Kd) for interaction of galectin-3 and the glycosylated MUC1 fragments measured by ITC decreased up to 10 times in comparison to the free TF disaccharide. No binding was observed for the non-glycosylated control version of the MUC1 peptide. The most notable feature of the binding of MUC1-glycopeptides to galectin-3 was a shift from a favorable enthalpy to an entropy-driven binding process. The comparatively diminished enthalpy contribution to the free energy (ΔG) was compensated by a considerable gain in the entropic term. (1)H-(15)N HSQC NMR data reveal contact at the canonical site mainly by the glycan moiety of MUC1 glycopeptide. Ligand-dependent differences in binding affinities were also confirmed by a novel assay for screening of low-affinity glycan-lectin interactions based on AlphaScreen technology. Another key finding is that the glycosylated MUC1 peptides exhibited activity in a concentration-dependent manner in cell-based assays revealing selectivity among human galectins. Thus, the presentation of this tumor-associated carbohydrate ligand by the natural peptide scaffold enhances its affinity, highlighting the significance of model studies of human lectins with synthetic glycopeptides.
[Show abstract][Hide abstract] ABSTRACT: The specific interaction of ganglioside GM1 with the homodimeric (prototype) endogenous lectin galectin-1 triggers growth regulation in tumor and activated effector T cells. This proven biorelevance directed interest to studying association of the lectin to a model surface, i.e. a 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine/ganglioside GM1 (80: 20 mol%) monolayer, at a bioeffective concentration. Surface expansion by the lectin insertion was detected at a surface pressure of 20 mN/m. On combining the methods of grazing incidence X-ray diffraction and X-ray reflectivity, a transient decrease in lipid-ordered phase of the monolayer was observed. The measured electron density distribution indicated that galectin-1 is oriented with its long axis in the surface plane, ideal for cis-crosslinking. The data reveal a conspicuous difference to the way the pentameric lectin part of the cholera toxin, another GM1-specific lectin, is bound to the monolayer. They also encourage further efforts to monitor effects of structurally different members of the galectin family such as the functionally antagonistic chimera-type galectin-3.
No preview · Article · Jul 2015 · Biochemistry (Moscow)
[Show abstract][Hide abstract] ABSTRACT: Lectins translate information encoded in glycan chains of cellular glycoconjugates into bioeffects. The topological presentation of contact sites for cognate sugar binding is a crucial factor toward this end. To dissect the significance of such phylogenetically conserved properties, the design and engineering of non-natural variants are attractive approaches. Here, a homodimeric human lectin, i.e. adhesion/growth-regulatory galectin-1, is converted into a tandem-repeat display by introducing the 33-amino-acid linker of another family member (i.e. galectin-8). The yield of variant was reduced by about a third. This protein had ∼10-fold higher activity in hemagglutination. Nearly complete sequence determination by mass-spectrometric in-source decay and fingerprinting excluded the presence of any modifications. When 1H-15N heteronuclear single-quantum coherence data on the 15N-labeled variant and wild-type protein were compared, changes in chemical shifts, signal intensities and resonance multiplicities revealed reduction of stability of interfacial contacts between the lectin domains and an increase in inter-domain flexibility. When both binding sites in the variant were loaded with ligand, association of the two carbohydrate recognition domains was enhanced, corroborated by gel filtration. Dynamic changes in the spatial presentation of the two lectin domains in the context of a tandem-repeat display can alter counterreceptor targeting relative to the fixed positions found in the proto-type galectin homodimer.
No preview · Article · Jul 2015 · Protein Engineering Design and Selection
[Show abstract][Hide abstract] ABSTRACT: The emerging physiological significance of carbohydrate (glycan)–protein (lectin) recognition engenders the interest to design synthetic inhibitors with a high level of selectivity among natural sugar receptors. Plant agglutinins are common models to determine structure–activity relationships. Focussing on the contribution of valency towards selectivity, copper-catalysed azide (sugar derivative)–alkyne (scaffold) cycloaddition yielded a panel of 10 bi- to tetravalent glycoclusters with N-acetylglucosamine as the bioactive headgroup. They were introduced into assays using (neo)glycoproteins and cell surfaces as platforms to study carbohydrate-dependent lectin binding. The ability of the bivalent compounds, which exhibit a distance profile of the sugar headgroups of about 16–21 Å, for intramolecular bridging of two contact sites from the eight hevein domains of wheat germ agglutinin led to comparatively high enhancements of inhibitory potency relative to a tetrameric leguminous lectin (distance profile of 50–70 Å between sugar-specific sites), especially for a β-S-glycoside. The extent of inhibition at fixed concentrations of the sugar depended on the type of matrix used for the assay. Increases to tri- and tetravalency played a less important role than the anomeric position to keep cross-reactivity low, these tested topologies enabling cross-linking for both lectins. The potential for cis-interactions (intramolecular interactions), with glycoclusters serving as molecular rulers, is suggested to help designing selective blocking reagents.
[Show abstract][Hide abstract] ABSTRACT: The increasing evidence for the physiological significance of glycan-protein (lectin) interactions prompts considerations for respective bioactivity of plant polysaccharides. Arabinogalactan from larch, a polysaccharide with a β1,3-linked galactose core and branches at the 6'-hydroxyl, was thus tested, together with two processed forms treated either with oxalic or trifluoroacetic acid. Hydrolysis by acid reduced the arabinose contents without backbone degradation. The three preparations were tested as an inhibitor of lectin binding in solid-phase and cell-based assays, using the toxin from Viscum album and a panel of seven human lectins (six galectins and a C-type lectin). Increasing potency correlating with the molecular contents of galactose was seen for the plant toxin. In general, relatively weak or no inhibitory capacity was detected for the three preparations, when binding of the human galectins and avian orthologues used as controls was measured. Acid-treated polysaccharides also weakly interfered with binding of the galactose-specific C-type lectin of human macrophages. Larch arabinogalactan, tested as a model, will thus most likely not impair (ga)lectin functionality physiologically.
Georg Thieme Verlag KG Stuttgart · New York.
[Show abstract][Hide abstract] ABSTRACT: Surface-presented glycans (complex carbohydrates) are docking sites for adhesion/growth-regulatory galectins within cell-cell/matrix interactions. Alteration of the linker length in human galectin-8 and single-site mutation (F19Y) are used herein to illustrate the potential of glycodendrimersomes with programmable glycan displays as a model system to reveal the functional impact of natural sequence variations in trans recognition. Extension of the linker length slightly reduces lectin capacity as agglutinin and slows down aggregate formation at low ligand surface density. The mutant protein is considerably less active as agglutinin and less sensitive to low-level ligand presentation. The present results suggest that mimicking glycan complexity and microdomain occurrence on the glycodendrimersome surface can provide key insights into mechanisms to accomplish natural selectivity and specificity of lectins in structural and topological terms.
No preview · Article · May 2015 · Proceedings of the National Academy of Sciences