Galectin-13, a different prototype galectin, does not bind β-galacto-sides and forms dimers via intermolecular disulfide bridges between Cys-136 and Cys-138

Modulation of galectin-9 mediated responses in monocytes and T-cells by pregnancy-specific glycoprotein 1

Successful pregnancy relies on a coordinated interplay between endocrine, immune, and metabolic processes to sustain fetal growth and development. The orchestration of these processes involves multiple signaling pathways driving cell proliferation, differentiation, angiogenesis, and immune regulation necessary for a healthy pregnancy. Among the molecules supporting placental development and maternal tolerance, the families of pregnancy-specific glycoproteins and galectins are of great interest in reproductive biology. We previously found that PSG1 can bind to galectin-1 (GAL-1). Herein, we characterized the interaction between PSG1 and other members of the galectin family expressed during pregnancy, including galectin-3, -7, -9, and -13 (GAL-3, GAL-7, GAL-9, and GAL-13). We observed that PSG1 binds to GAL-1, -3, and -9, with the highest apparent affinity seen for GAL-9, and that the interaction of PSG1 with GAL-9 is carbohydrate-dependent. We further investigated the ability of PSG1 to regulate GAL-9 responses in human monocytes, a murine macrophage cell line, and T-cells, and determined whether PSG1 binds to both carbohydrate recognition domains of GAL-9. Additionally, we compared the apparent affinity of GAL-9 binding to PSG1 with other known GAL-9 ligands in these cells, Tim-3 and CD44. Lastly, we explored functional conservation between murine and human PSGs by determining that Psg23, a highly expressed member of the murine Psg family, can bind some murine galectins despite differences in amino acid composition and domain structure.

Placental galectins: a subfamily of galectins lose the ability to bind β-galactosides with new structural features†

Galectins are a phylogenetically conserved family of soluble β-galactoside binding proteins. There are 16 different of galectins, each with a specific function determined by its distinct distribution and spatial structure. Galectin-13, galectin-14, and galectin-16 are distinct from other galectin members in that they are primarily found in placental tissue. These galectins, also referred to as placental galectins, play critical roles in regulating pregnancy-associated processes, such as placenta formation and maternal immune tolerance to the embedded embryo. The unique structural characteristics and the inability to bind lactose of placental galectins have recently received significant attention. This review primarily examines the novel structural features of placental galectins, which distinguish them from the classic galectins. Furthermore, it explores the correlation between these structural features and the loss of β-galactoside binding ability. In addition, the newly discovered functions of placental galectins in recent years are also summarized in our review. A detailed understanding of the roles of placental galectins may contribute to the discovery of new mechanisms causing numerous pregnancy diseases and enable the development of new diagnostic and therapeutic strategies for the treatment of these diseases, ultimately benefiting the health of mothers and offspring.

Glutathione disrupts galectin-10 Charcot-Leyden crystal formation to possibly ameliorate eosinophil-based diseases such as asthma

Charcot-Leyden crystals (CLCs) are the hallmark of many eosinophilic-based diseases, such as asthma. Here, we report that reduced glutathione (GSH) disrupts CLCs and inhibits crystallization of human galectin-10 (Gal-10). GSH has no effect on CLCs from monkeys ( Macaca fascicularis or M. mulatta), even though monkey Gal-10s contain Cys29 and Cys32. Interestingly, human Gal-10 contains another cysteine residue (Cys57). Because GSH cannot disrupt CLCs formed by the human Gal-10 variant C57A or inhibit its crystallization, the effects of GSH on human Gal-10 or CLCs most likely occur by chemical modification of Cys57. We further report the crystal structures of Gal-10 from M. fascicularis and M. mulatta, along with their ability to bind to lactose and inhibit erythrocyte agglutination. Structural comparison with human Gal-10 shows that Cys57 and Gln75 within the ligand binding site are responsible for the loss of lactose binding. Pull-down experiments and mass spectrometry show that human Gal-10 interacts with tubulin α-1B, with GSH, GTP and Mg ²⁺ stabilizing this interaction and colchicine inhibiting it. Overall, this study enhances our understanding of Gal-10 function and CLC formation and suggests that GSH may be used as a pharmaceutical agent to ameliorate CLC-induced diseases.

Placental Galectins in Cancer: Why We Should Pay More Attention

The first studies suggesting that abnormal expression of galectins is associated with cancer were published more than 30 years ago. Today, the role of galectins in cancer is relatively well established. We know that galectins play an active role in many types of cancer by regulating cell growth, conferring cell death resistance, or inducing local and systemic immunosuppression, allowing tumor cells to escape the host immune response. However, most of these studies have focused on very few galectins, most notably galectin-1 and galectin-3, and more recently, galectin-7 and galectin-9. Whether other galectins play a role in cancer remains unclear. This is particularly true for placental galectins, a subgroup that includes galectin-13, -14, and -16. The role of these galectins in placental development has been well described, and excellent reviews on their role during pregnancy have been published. At first sight, it was considered unlikely that placental galectins were involved in cancer. Yet, placentation and cancer progression share several cellular and molecular features, including cell invasion, immune tolerance and vascular remodeling. The development of new research tools and the concomitant increase in database repositories for high throughput gene expression data of normal and cancer tissues provide a new opportunity to examine the potential involvement of placental galectins in cancer. In this review, we discuss the possible roles of placental galectins in cancer progression and why they should be considered in cancer studies. We also address challenges associated with developing novel research tools to investigate their protumorigenic functions and design highly specific therapeutic drugs.

Galectin functions in cancer-associated inflammation and thrombosis

Galectins are carbohydrate-binding proteins that regulate many cellular functions including proliferation, adhesion, migration, and phagocytosis. Increasing experimental and clinical evidence indicates that galectins influence many steps of cancer development by inducing the recruitment of immune cells to the inflammatory sites and modulating the effector function of neutrophils, monocytes, and lymphocytes. Recent studies described that different isoforms of galectins can induce platelet adhesion, aggregation, and granule release through the interaction with platelet-specific glycoproteins and integrins. Patients with cancer and/or deep-venous thrombosis have increased levels of galectins in the vasculature, suggesting that these proteins could be important contributors to cancer-associated inflammation and thrombosis. In this review, we summarize the pathological role of galectins in inflammatory and thrombotic events, influencing tumor progression and metastasis. We also discuss the potential of anti-cancer therapies targeting galectins in the pathological context of cancer-associated inflammation and thrombosis.

Medawar's PostEra: Galectins Emerged as Key Players During Fetal-Maternal Glycoimmune Adaptation

Lectin-glycan interactions, in particular those mediated by the galectin family, regulate many processes required for a successful pregnancy. Over the past decades, increasing evidence gathered from in vitro and in vivo experiments indicate that members of the galectin family specifically bind to both intracellular and membrane bound carbohydrate ligands regulating angiogenesis, immune-cell adaptations required to tolerate the fetal semi-allograft and mammalian embryogenesis. Therefore, galectins play important roles in fetal development and placentation contributing to maternal and fetal health. This review discusses the expression and role of galectins during the course of pregnancy, with an emphasis on maternal immune adaptions and galectin-glycan interactions uncovered in the recent years. In addition, we summarize the galectin fingerprints associated with pathological gestation with particular focus on preeclampsia.

Molecular characterization and expression profiling of tandem-repeat galectin-8 from red-spotted grouper (Epinephelus akaara): Potential antibacterial, antiviral, and wound healing activities

Galectin-8 is a typical β-galactoside binding lectin, which primarily functions as a pattern recognition receptor and/or danger receptor that is engaged in pathogen recognition by the host innate immune system. Although several fish galectins have been identified, the role of galectin-8 in teleost immunity is still not fully understood. In this study, molecular, transcriptional, and immune-related functions of galectin-8 (EaGal8) from red-spotted grouper (Epinephelus akaara) were analyzed. The open reading frame of EaGal8 comprised 960 bp encoding 319 amino acids of a ∼35 kDa protein, composed of the N- and C-terminal carbohydrate recognition domains joined by a short hinge peptide. Phylogenetic analysis revealed that EaGal8 was closely related to the Epinephelus lanceolatus galectin-8-like protein. Although EaGal8 showed ubiquitous tissue expression, the highest expression level was observed in the blood. Immunostimulants, including lipopolysaccharide, poly(I:C), and nervous necrosis virus, significantly upregulated the EaGal8 transcription level in a time-dependent manner (p < 0.05). Furthermore, recombinant EaGal8 (rEaGal8) showed a binding affinity toward seven different carbohydrates in a concentration-dependent manner. In addition, rEaGal8 caused strong agglutination of fish red blood cells and several gram-positive and gram-negative bacteria, including Streptococcus iniae, Streptococcus parauberis, Lactococcus garvieae, Escherichia coli, Edwardsiella tarda, Vibrio alginolyticus, Vibrio parahaemolyticus, and Pseudomonas aeruginosa. For the first time in teleosts, we report the wound healing ability of galectin-8 in this study. At low concentrations, rEaGal8 showed potential wound healing responses in FHM cells, in vitro. Thus, this study reinforces the role of EaGal8 in innate immune responses against bacterial and viral infections and wound healing in red-spotted grouper.

Modulation of the Gal-9/TIM-3 Immune Checkpoint with α-Lactose. Does Anomery of Lactose Matter?

Simple Summary

The disaccharide lactose is a common excipient in pharmaceutical products. In addition, the two anomers α- and β-lactose can exert immuno-modulatory effects. α-Lactose functions as a major regulator of the T-cell immunoglobulin mucin-3 (Tim-3)/Galectin-9 (Gal-9) immune checkpoint, through direct binding to the β-galactoside-binding lectin galectin-9. The blockade of TIM-3 with monoclonal antibodies or small molecules represents a promising approach to combat onco-hematological diseases, in particular myelodysplastic syndromes, and acute myeloid leukemia. Alternatively, the activity of the checkpoint can be modulated via targeting of Gal-9 with both α- and β-lactose. In fact, lactose is a quasi-pan-galectin ligand, capable of modulating the functions of most of the 16 galectin molecules. This review discusses the capacity of lactose and Gal-9 to modulate the TIM-3/Gal-9 and PD-1/PD-L1 immune checkpoints in oncology. The immuno-regulatory roles of lactose and Gal-9 are highlighted.

Abstract

The disaccharide lactose is an excipient commonly used in pharmaceutical products. The two anomers, α- and β-lactose (α-L/β-L), differ by the orientation of the C-1 hydroxyl group on the glucose unit. In aqueous solution, a mutarotation process leads to an equilibrium of about 40% α-L and 60% β-L at room temperature. Beyond a pharmaceutical excipient in solid products, α-L has immuno-modulatory effects and functions as a major regulator of TIM-3/Gal-9 immune checkpoint, through direct binding to the β-galactoside-binding lectin galectin-9. The blockade of the co-inhibitory checkpoint TIM-3 expressed on T cells with anti-TIM-3 antibodies represents a promising approach to combat different onco-hematological diseases, in particular myelodysplastic syndromes and acute myeloid leukemia. In parallel, the discovery and development of anti-TIM-3 small molecule ligands is emerging, including peptides, RNA aptamers and a few specifically designed heterocyclic molecules. An alternative option consists of targeting the different ligands of TIM-3, notably Gal-9 recognized by α-lactose. Modulation of the TIM-3/Gal-9 checkpoint can be achieved with both α- and β-lactose. Moreover, lactose is a quasi-pan-galectin ligand, capable of modulating the functions of most of the 16 galectin molecules. The present review provides a complete analysis of the pharmaceutical and galectin-related biological functions of (α/β)-lactose. A focus is made on the capacity of lactose and Gal-9 to modulate both the TIM-3/Gal-9 and PD-1/PD-L1 immune checkpoints in oncology. Modulation of the TIM-3/Gal-9 checkpoint is a promising approach for the treatment of cancers and the role of lactose in this context is discussed. The review highlights the immuno-regulatory functions of lactose, and the benefit of the molecule well beyond its use as a pharmaceutical excipient.

Actin binding to galectin-13/placental protein-13 occurs independently of the galectin canonical ligand binding site

The gene for galectin-13 (Gal-13, placental protein 13) is only present in primates, and its low expression level in maternal serum may promote pre-eclampsia. In the present study, we used pull-down experiments and biolayer interferometry to assess the interaction between Gal-13 and actin. These studies uncovered that human Gal-13 (hGal-13) and Saimiri boliviensis boliviensis (sGal-13) strongly bind to α- and β/γ-actin, with Ca2+ and ATP significantly enhancing interactions. This in turn suggests that h/sGal-13 may inhibit myosin-induced contraction when vascular smooth muscle cells undergo polarization. Here, we solved the crystal structure of sGal-13 bound to lactose and found that it exists as a monomer in contrast to hGal-13 that is a dimer. The distribution of sGal-13 in HeLa cells is similar to that of hGal-13, indicating that monomeric Gal-13 is the primary form in cells. Even though sGal-13 also binds to actin, hGal-13 ligand binding site mutants do not influence hGal-13/actin binding, whereas the monomeric mutant C136S/C138S binds to actin more strongly than wild type hGal-13. Overall, our study demonstrates that monomeric Gal-13 binds to actin, an interaction that is independent of the galectin canonical ligand binding site.

Degraded Arabinogalactans and Their Binding Properties to Cancer-Associated Human Galectins

Galectins represent β-galactoside-binding proteins with numerous functions. Due to their role in tumor progression, human galectins-1, -3 and -7 (Gal-1, -3 and -7) are potential targets for cancer therapy. As plant derived glycans might act as galectin inhibitors, we prepared galactans by partial degradation of plant arabinogalactan-proteins. Besides commercially purchased galectins, we produced Gal-1 and -7 in a cell free system and tested binding capacities of the galectins to the galactans by biolayer-interferometry. Results for commercial and cell-free expressed galectins were comparable confirming functionality of the cell-free produced galectins. Our results revealed that galactans from Echinacea purpurea bind to Gal-1 and -7 with K_D values of 1–2 µM and to Gal-3 slightly stronger with K_D values between 0.36 and 0.70 µM depending on the sensor type. Galactans from the seagrass Zostera marina with higher branching of the galactan and higher content of uronic acids showed stronger binding to Gal-3 (0.08–0.28 µM) compared to galactan from Echinacea. The results contribute to knowledge on interactions between plant polysaccharides and galectins. Arabinogalactan-proteins have been identified as a new source for production of galactans with possible capability to act as galectin inhibitors.

Human Lectins, Their Carbohydrate Affinities and Where to Find Them

Lectins are a class of proteins responsible for several biological roles such as cell-cell interactions, signaling pathways, and several innate immune responses against pathogens. Since lectins are able to bind to carbohydrates, they can be a viable target for targeted drug delivery systems. In fact, several lectins were approved by Food and Drug Administration for that purpose. Information about specific carbohydrate recognition by lectin receptors was gathered herein, plus the specific organs where those lectins can be found within the human body.

Galectin-13/placental protein 13: redox-active disulfides as switches for regulating structure, function and cellular distribution

Galectin-13 (Gal-13) plays numerous roles in regulating the relationship between maternal and fetal tissues. Low expression levels or mutations of the lectin can result in pre-eclampsia. The previous crystal structure and gel filtration data show that Gal-13 dimerizes via formation of two disulfide bonds formed by Cys136 and Cys138. In the present study, we mutated them to serine (C136S, C138S and C136S/C138S), crystalized the variants and solved their crystal structures. All variants crystallized as monomers. In the C136S structure, Cys138 formed a disulfide bond with Cys19, indicating that Cys19 is important for regulation of reversible disulfide bond formation in this lectin. Hemagglutination assays demonstrated that all variants are inactive at inducing erythrocyte agglutination, even though gel filtration profiles indicate that C136S and C138S could still form dimers, suggesting that these dimers do not exhibit the same activity as wild-type (WT) Gal-13. In HeLa cells, the three variants were found to be distributed the same as with WT Gal-13. However, a Gal-13 variant (delT221) truncated at T221 could not be transported into the nucleus, possibly explaining why women having this variant get pre-eclampsia. Considering the normally high concentration of glutathione in cells, WT Gal-13 should exist mostly as a monomer in cytoplasm, consistent with the monomeric variant C136S/C138S, which has a similar ability to interact with HOXA1 as WT Gal-13.

Human galectin-16 has a pseudo ligand binding site and plays a role in regulating c-Rel-mediated lymphocyte activity

BACKGROUND

The structure of human galectin-16 (Gal-16) has yet to be solved, and its function has remained elusive.

METHODS

X-ray crystallography was used to determine the atomic structures of Gal-16 and two of its mutants. The Gal-16 oligomer state was investigated by gel filtration, its hemagglutination activity was determined along with its ability to bind lactose using ITC. The cellular distribution of EGFP-tagged Gal-16 in various cell lines was also investigated, and the interaction between Gal-16 and c-Rel was assessed by pull-down studies, microscale thermophoresis and immunofluorescence.

RESULTS

Unlike other galectins, Gal-16 lacks the ability to bind the β-galactoside lactose. Lactose binding could be regained by replacing an arginine (Arg55) with asparagine, as shown in the crystal structures of two lactose-loaded Gal-16 mutants (R55N and R55N/H57R). Gal-16 was also shown to be monomeric by gel filtration, as well as in crystal structures. Thus, this galectin could not induce erythrocyte agglutination. EGFP-tagged Gal-16 was found to be localized mostly in the nucleus of various cell types, and can interact with c-Rel, a member of NF-κB family.

CONCLUSIONS

Gal-16 exists as a monomer and its ligand binding is significantly different from that of other prototype galectins, suggesting that it has a novel function(s). The interaction between Gal-16 and c-Rel indicates that Gal-16 may regulate signal transduction pathways via the c-Rel hub in B or T cells at the maternal-fetal interface.

GENERAL SIGNIFICANCE

The present study lays the foundation for further studies into the cellular and physiological functions of Gal-16.

Glycan expression in chorionic villi from histocultures of women with early-onset preeclampsia: Immunomodulatory effects on peripheral natural killer cells

New evidence suggests that glycan expression in placental cells of women with invasive disorders of pregnancy differs from that in normal pregnant women. Hypothesizing that modifications of glycan expression could account for the course of preeclampsia, we established placental villous histocultures and compared glycan expression in women with preeclampsia with that in normal pregnant women and also in syncytialized BeWo cells, and we tested the effect of glycan expression on the functional phenotypes of circulating natural killer (NK) cells. Histocultures of third-trimester placentae from women with preeclampsia and full-term placentae from healthy pregnant women and BeWo choriocarcinoma cells were assessed for the expression of terminal glycans by lectin-binding assays. Circulating NK cells from nonpregnant healthy donors were tested in vitro for their cytotoxic activity and intracellular cytokine content. Histocultures from women with preeclampsia expressed significantly more mannose than did those from healthy pregnant women. Both histocultures and BeWo cells expressed terminal fucose, mannose, sialic acid, and N -acetylgalactosamine, although mean fluorescence intensity (MFI) expression was lower in choriocarcinoma cells than in cells from histocultures. Cocultures of circulating NK cells with K562 target cells resulted in a dose-dependent cytotoxicity effect, but the use of BeWo cells as target reduced cytotoxic activity; this reduction was not affected by syncytialization. Histocultures of placental villous tissue of women with preeclampsia expressed high levels of terminal mannose. We proposethat placental glycans may modulate the functional activity of circulating NK cells in the context of systemic inflammatory response in preeclampsia.

Structure-function studies of galectin-14, an important effector molecule in embryology

The expression of prototype galectin-14 (Gal-14) in human placenta is higher than any other galectin, suggesting that it may play a role in fetal development and regulation of immune tolerance during pregnancy. Here, we solved the crystal structure of dimeric Gal-14 and found that its global fold is significantly different from that of other galectins with two β-strands (S5 and S6) extending from one monomer and contributing to the carbohydrate-binding domain of the other. The hemagglutination assay showed that this lectin could induce agglutination of chicken erythrocytes, even though lactose could not inhibit Gal-14-induced agglutination activity. Calorimetry indicates that lactose does not interact with this lectin. Compared to galectin-1, galectin-3, and galectin-8, Gal-14 has two key amino acids (a histidine and an arginine) in the normally conserved, canonical sugar-binding site, which are substituted by glutamine (Gln53) and histidine (His57), thus likely explaining why lactose binding to this lectin is very weak. Lactose was observed in the ligand-binding site of one Gal-14 structure, most likely because ligand binding is weak and crystals were allowed to grow over a long period of time in the presence of lactose. We also found that EGFP-tagged Gal-14 is primarily localized within the nucleus of different cell types. In addition, Gal-14 colocalized with c-Rel (a member of NF-κB family) in HeLa cells. These findings indicate that Gal-14 might regulate signal transduction pathways through NF-κB hubs. Overall, the present study provides impetus for further research into the function of Gal-14 in embryology.

Glycan characterization of pregnancy-specific glycoprotein 1 and its identification as a novel Galectin-1 ligand

Pregnancy-specific beta 1 glycoprotein (PSG1) is secreted from trophoblast cells of the human placenta in increasing concentrations as pregnancy progresses, becoming one of the most abundant proteins in maternal serum in the third trimester. PSG1 has seven potential N-linked glycosylation sites across its four domains. We carried out glycomic and glycoproteomic studies to characterize the glycan composition of PSG1 purified from serum of pregnant women and identified the presence of complex N-glycans containing poly LacNAc epitopes with α2,3 sialyation at four sites. Using different techniques, we explored whether PSG1 can bind to galectin-1 (Gal-1) as these two proteins were previously shown to participate in processes required for a successful pregnancy. We confirmed that PSG1 binds to Gal-1 in a carbohydrate-dependent manner with an affinity of the interaction of 0.13 μM. In addition, we determined that out of the three N-glycosylation-carrying domains, only the N and A2 domains of recombinant PSG1 interact with Gal-1. Lastly, we observed that the interaction between PSG1 and Gal-1 protects this lectin from oxidative inactivation and that PSG1 competes the ability of Gal-1 to bind to some but not all of its glycoprotein ligands.

Structures of human galectin-10/monosaccharide complexes demonstrate potential of monosaccharides as effectors in forming Charcot-Leyden crystals

The galectins are a family of β-galactoside-specific animal lectins, and have attracted much attention as novel regulators of the immune system. Galectin-10 is well-expressed in eosinophils, and spontaneously forms Charcot-Leyden crystals (CLCs), during prolonged eosinophilic inflammatory reactions, which are frequently observed in eosinophilic diseases. Although biochemical and structural characterizations of galectin-10 have been done, its biological role and molecular mechanism are still unclear, and few X-ray structures of galectin-10 in complex with monosaccharides/oligosaccharides have been reported. Here, X-ray structures of galectin-10 in complexes with seven monosaccharides are presented with biochemical analyses to detect interactions of galectin-10 with monosaccharides/oligosaccharides. Galectin-10 forms a homo-dimer in the face-to-face orientation, and the monosaccharides bind to the carbohydrate recognition site composed of amino acid residues from two galectin-10 molecules of dimers, suggesting that galectin-10 dimer likely captures the monosaccharides in solution and in vivo. d-Glucose, d-allose, d-arabinose, and D-N-acetylgalactosamine bind to the interfaces between galectin-10 dimers in crystals, and they affect the stability of molecular packing in crystals, leading to easy-dissolving of CLCs, and/or inhibiting the formation of CLCs. These monosaccharides may serve as effectors of G10 to form CLCs in vivo.

Charcot-Leyden crystal protein/galectin-10 interacts with cationic ribonucleases and is required for eosinophil granulogenesis

BACKGROUND

The human eosinophil Charcot-Leyden crystal (CLC) protein is a member of the Galectin superfamily and is also known as galectin-10 (Gal-10). CLC/Gal-10 forms the distinctive hexagonal bipyramidal crystals that are considered hallmarks of eosinophil participation in allergic responses and related inflammatory reactions; however, the glycan-containing ligands of CLC/Gal-10, its cellular function(s), and its role(s) in allergic diseases are unknown.

OBJECTIVE

We sought to determine the binding partners of CLC/Gal-10 and elucidate its role in eosinophil biology.

METHODS

Intracellular binding partners were determined by ligand blotting with CLC/Gal-10, followed by coimmunoprecipitation and coaffinity purifications. The role of CLC/Gal-10 in eosinophil function was determined by using enzyme activity assays, confocal microscopy, and short hairpin RNA knockout of CLC/Gal-10 expression in human CD34⁺ cord blood hematopoietic progenitors differentiated to eosinophils.

RESULTS

CLC/Gal-10 interacts with both human eosinophil granule cationic ribonucleases (RNases), namely, eosinophil-derived neurotoxin (RNS2) and eosinophil cationic protein (RNS3), and with murine eosinophil-associated RNases. The interaction is independent of glycosylation and is not inhibitory toward endoRNase activity. Activation of eosinophils with INF-γ induces the rapid colocalization of CLC/Gal-10 with eosinophil-derived neurotoxin/RNS2 and CD63. Short hairpin RNA knockdown of CLC/Gal-10 in human cord blood-derived CD34⁺ progenitor cells impairs eosinophil granulogenesis.

CONCLUSIONS

CLC/Gal-10 functions as a carrier for the sequestration and vesicular transport of the potent eosinophil granule cationic RNases during both differentiation and degranulation, enabling their intracellular packaging and extracellular functions in allergic inflammation.

Intrinsic tryptophan fluorescence spectroscopy reliably determines galectin-ligand interactions

Galectins are involved in the regulation of divergent physiological and pathological processes and are increasingly recognized to play important roles in a number of diseases. However, a simple and effective way in assessing galectin-ligand interactions is lacking. Our examination of the sequence of all 12 human galectin members reveals the presence of one or more tryptophan residues in the carbohydrate-recognition domains of each galectin. This led us to investigate the possibility that alteration of the galectin intrinsic tryptophan fluorescence could be used in determining the strength of galectin-ligand interactions. One representative member from each of the three subtype galectins, galectin-2 (proto-), galectin-3 (chimera-) and galectin-4 (tandem repeat-type), was selected and analysed for galectin interaction with three ligands of different affinities: galactose, lactose and N-acetyl-lactosamine using tryptophan fluorescence spectroscopy (TFS) and, as a comparison, isothermal titration calorimetry (ITC). Good agreement between TFS and ITC measurements were revealed in ligand bindings of all galectin members. Moreover, TFS detected very weak galectin binding where ITC could not reliably do so. The reliability of TFS in determining galectin-ligand interactions was further validated by analysis of galectin-3 interaction with a semisynthetic ligand, F3. Thus, TFS can be used as a simple, sensitive and reliable way to determine galectin-ligand interactions and also as a drug-discovery platform in developing galectin-targeted therapeutic drugs.

Pregnancy Galectinology: Insights Into a Complex Network of Glycan Binding Proteins

Galectins are a phylogenetically conserved family of soluble β-galactoside binding proteins, consisting of 15 different types, each with a specific function. Galectins contribute to placentation by regulating trophoblast development, migration, and invasion during early pregnancy. In addition, galectins are critical players regulating maternal immune tolerance to the embedded embryo. Recently, the role of galectins in angiogenesis during decidualization and in placenta formation has gained attention. Altered expression of galectins is associated with abnormal pregnancies and infertility. This review focuses on the role of galectins in pregnancy-associated processes and discusses the relevance of galectin-glycan interactions as potential therapeutic targets in pregnancy disorders.

Resetting the ligand binding site of placental protein 13/galectin-13 recovers its ability to bind lactose

Placental protein 13/galectin-13 (Gal-13) is highly expressed in placenta, where its lower expression is related to pre-eclampsia. Recently, the crystal structures of wild-type Gal-13 and its variant R53H at high resolution were solved. The crystallographic and biochemical results showed that Gal-13 and R53H could not bind lactose. Here, we used site-directed mutagenesis to re-engineer the ligand binding site of wild-type Gal-13, so that it could bind lactose. Of six newly engineered mutants, we were able to solve the crystal structures of four of them. Three variants (R53HH57R, R53HH57RD33G and R53HR55NH57RD33G had the same two mutations (R53 to H, and H57 to R) and were able to bind lactose in the crystal, indicating that these mutations were sufficient for recovering the ability of Gal-13 to bind lactose. Moreover, the structures of R53H and R53HR55N show that these variants could co-crystallize with a molecule of Tris. Surprisingly, although these variants, as well as wild-type Gal-13, could all induce hemagglutination, high concentrations of lactose could not inhibit agglutination, nor could they bind to lactose-modified Sepharose 6b beads. Overall, our results indicate that Gal-3 is not a normal galectin, which could not bind to β-galactosides. Lastly, the distribution of EGFP-tagged wild-type Gal-13 and its variants in HeLa cells showed that they are concentrated in the nucleus and could be co-localized within filamentary materials, possibly actin.

A Brief History of Charcot-Leyden Crystal Protein/Galectin-10 Research

Eosinophils are present in tissues, such as the respiratory tract, spleen, lymph nodes and blood vessels. The significant presence of eosinophils in these tissues are associated with various diseases, including asthma, allergies, acute myeloid leukemia, etc. Charcot-Leyden crystal protein/galectin-10 is overexpressed in eosinophils and has also been identified in basophils and macrophages. In human body, this protein could spontaneously form Charcot-Leyden crystal in lymphocytes or in the lysates of lymphocytes. At present, the role of Charcot-Leyden crystal protein/galectin-10 in lymphocytes is not fully understood. This review summarizes research progress on Charcot-Leyden crystal protein/galectin-10, with emphasis on its history, cellular distributions, relations to diseases, structures and ligand binding specificity.

Selection scan reveals three new loci related to high altitude adaptation in Native Andeans

The Andean Altiplano has been occupied continuously since the late Pleistocene, ~12,000 years ago, which places the Andean natives as one of the most ancient populations living at high altitudes. In the present study, we analyzed genomic data from Native Americans living a long-time at Andean high altitude and at Amazonia and Mesoamerica lowland areas. We have identified three new candidate genes - SP100, DUOX2 and CLC - with evidence of positive selection for altitude adaptation in Andeans. These genes are involved in the TP53 pathway and are related to physiological routes important for high-altitude hypoxia response, such as those linked to increased angiogenesis, skeletal muscle adaptations, and immune functions at the fetus-maternal interface. Our results, combined with other studies, showed that Andeans have adapted to the Altiplano in different ways and using distinct molecular strategies as compared to those of other natives living at high altitudes.