Dependent Lectin Research Articles

Coarse-Graining the Recognition of a Glycolipid by the C-Type Lectin Mincle Receptor.

Macrophage inducible Ca2+-dependent lectin (Mincle) receptor recognizes Mycobacterium tuberculosis glycolipids to trigger an immune response. This host membrane receptor is thus a key player in the modulation of the immune response to infection by M. tuberculosis and has emerged as a promising target for the development of new vaccines against tuberculosis. The recent development of the Martini 3 force field for coarse-grained (CG) molecular modeling allows the study of interactions of soluble proteins with small ligands which was not typically modeled well with the previous Martini 2 model. Here, we present a refined approach detailing a protocol for modeling interactions between a glycolipid and its receptor at a CG level using the Martini 3 force field. Using this approach, we studied Mincle and identified critical parameters governing ligand recognition, such as loop flexibility and the regulation of hydrophobic groove formation by calcium ions. In addition, we assessed ligand affinity using free energy perturbation calculations. Our results offer mechanistic insight into the interactions between Mincle and glycolipids, providing a basis for the rational design of molecules targeting this type of membrane receptors.

Oncolytic vaccinia virus harboring aphrocallistes vastus lectin exerts anti-tumor effects by directly oncolysis and inducing immune response through enhancing ROS in human ovarian cancer

Aphrocallistes vastus lectin (AVL) is a Ca2+ dependent C-type lectin produced by sponges. Previous studies have demonstrated that oncolytic vaccinia virus harboring AVL (oncoVV-AVL) effectively triggers cell death in various tumors. However, the effects of oncoVV-AVL on human ovarian cancer (OV) remain unknown. This study aims to investigate the mechanism-of-action of oncoVV-AVL in human OV cell lines and in tumor-bearing nude mice. We found that oncoVV-AVL could directly induce apoptosis and autophagy in ovarian cancer cells. Additionally, our results showed that oncoVV-AVL increased the serum levels of mouse IFN-γ (mIFN-γ), leading to the activation of M1-polarized macrophages. Conversely, NADPH, a reducing agent by providing reducing equivalents, reduced the production of mIFN-γ, and suppressed M1-polarization of macrophage. Based on these findings, we propose that oncoVV-AVL not only contributes to direct cytolysis, but also enhances host immune response by promoting ROS levels.

ROS Induced by Aphrocallistes vastus Lectin Enhance Oncolytic Vaccinia Virus Replication and Induce Apoptosis in Hepatocellular Carcinoma Cells.

Oncolytic virotherapy is expected to provide a new treatment strategy for cancer. Aphrocallistes vastus lectin (AVL) is a Ca2+-dependent lectin receptor containing the conserved domain of C-type lectin and the hydrophobic N-terminal region, which can bind to the bird's nest glycoprotein and D-galactose. Our previous studies suggested that the oncolytic vaccinia virus (oncoVV) armed with the AVL gene exerted remarkable replication and antitumor effects in vitro and in vivo. In this study, we found that oncoVV-AVL may reprogram the metabolism of hepatocellular carcinoma cells to promote ROS, and elevated ROS subsequently promoted viral replication and induced apoptosis. This study will provide a new theoretical basis for the application of oncoVV-AVL in liver cancer.

Isolation, characterization and antimicrobial properties of hepatopancreas lectin of the freshwater crab Oziotelphusanaga

Lectins are versatile proteins that specifically recognize and interact with sugar moieties expressed on the cell surface. The potential of lectin in drug targeting and delivery has instigated interest to identify natural lectins. Crabs have been identified as a rich source of lectin because the innate immune system is activated on encounter of pathogens and helps in the production of lectin. Although the presence of lectins in crab's hemolymph is well documented, little information about lectin in hepatopancreas, a vital organ for immunity and digestion in crustaceans, is currently available. A calcium dependent lectin (75 kDa) was purified from the hepatopancreas of the freshwater crab Oziotelphusa naga by bioadsorption and fetuin linked Sepharose 4B affinity chromatography technique. The isolated hepatopancreas lectin is calcium dependent and maximum agglutination was observed with rabbit erythrocytes. The hemagglutinating activity of the hepatopancreas lectin was effectively inhibited by sugars, such as α-lactose, GlcNAc, trehalose and NeuAc. Compared to sialylated N-glycosylated proteins including transferrin and apo transferrin, sialylated O-glycosylated proteins like fetuin exhibited stronger inhibitory effect. The ability of erythrocytes to bind hepatopancreas lectin has been diminished by desialylation of the potent inhibitor, indicating the significance of sialic acid in lectin-ligand interactions. The purified hepatopancreas lectin showed a broad spectrum of antimicrobial activity against bacteria Staphylococcus aureus, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, E. coli and fungi Candida albicans and Aspergillus niger. The findings of this study demonstrate the significance of hepatopancreas lectin as a multifunctional defense protein that inhibits the growth of bacteria and fungi.

Asymmetric Total Synthesis and Structural Revision of DAT2, an Antigenic Glycolipid from Mycobacterium tuberculosis.

DAT2 is a member of the diacyl trehalose family (DAT) of antigenic glycolipids located in the mycomembrane of Mycobacterium tuberculosis (Mtb). Recently it was shown that the molecular structure of DAT2 had been incorrectly assigned, but the correct structure remained elusive. Herein, the correct molecular structure of DAT2 and its methyl-branched acyl substituent mycolipanolic acid is determined. For this, four different stereoisomers of mycolipanolic acid were prepared in a stereoselective and unified manner, and incorporated into DAT2. A rigorous comparison of the four isomers to the DAT isolated from Mtb H37Rv by NMR, HPLC, GC, and mass spectrometry allowed a structural revision of mycolipanolic acid and DAT2. Activation of the macrophage inducible Ca2+-dependent lectin receptor (Mincle) with all four stereoisomers shows that the natural stereochemistry of mycolipanolic acid / DAT2 provides the strongest activation, which indicates its high antigenicity and potential application in serodiagnostics and vaccine adjuvants.

Asymmetric Total Synthesis and Structural Revision of DAT2, an Antigenic Glycolipid from Mycobacterium tuberculosis

AbstractDAT2 is a member of the diacyl trehalose family (DAT) of antigenic glycolipids located in the mycomembrane of Mycobacterium tuberculosis (Mtb). Recently it was shown that the molecular structure of DAT2 had been incorrectly assigned, but the correct structure remained elusive. Herein, the correct molecular structure of DAT2 and its methyl‐branched acyl substituent mycolipanolic acid is determined. For this, four different stereoisomers of mycolipanolic acid were prepared in a stereoselective and unified manner, and incorporated into DAT2. A rigorous comparison of the four isomers to the DAT isolated from Mtb H37Rv by NMR, HPLC, GC, and mass spectrometry allowed a structural revision of mycolipanolic acid and DAT2. Activation of the macrophage inducible Ca2+‐dependent lectin receptor (Mincle) with all four stereoisomers shows that the natural stereochemistry of mycolipanolic acid / DAT2 provides the strongest activation, which indicates its high antigenicity and potential application in serodiagnostics and vaccine adjuvants.

Identification, characterization, and agglutinating activity of a novel C-type lectin domain family 3 member B (CLEC3B) discovered in golden pompano, Trachinotus ovatus.

The lectins are a large family of carbohydrate-binding proteins that play important roles in the innate immune response of various organisms. Although C-type lectin domain family 3 member B (CLEC3B), an important member of C-type lectin, has been well documented in humans and several other higher vertebrates, little is currently known about this molecule in economically important marine fish species. In this study, through transcriptomic and BLAST screening, a novel CLEC3B gene was identified in the golden pompano (Trachinotus ovatus). The T. ovatus CLEC3B (ToCLEC3B) was subsequently characterized by bioinformatic analysis and compared with those reported in other species. In addition, the expression patterns of ToCLEC3B in different tissues under normal condition and at different times post pathogen challenge were assessed. Furthermore, the agglutinating activity of ToCLEC3B with and without Ca2+ against different bacteria and blood cells of donor species were verified using the recombinant T. ovatus CLEC3B (rToCLEC3B). Our results demonstrated that ToCLEC3B is a Ca2+-dependent galactose-binding lectin with a single copy of carbohydrate recognition domain (CRD). Similar to CLEC3B reported in other species, the CRD domain of ToCLEC3B consists of two α-helices, six β-sheets, and four loops, forming two Ca2+- and a galactose-binding sites. According to the phylogenetic analysis, the ToCLEC3B was highly similar (similarity at 95.00%) to that of its relative, the greater amberjack (Seriola dumerili). The expression of ToCLEC3B was detected in all tissues examined under normal condition and was significantly up-regulated by injection of pathogenic microbes. In addition, the rToCLEC3B exhibited strong agglutinating activity against different bacteria and blood cells of donor species in the presence of Ca2+. Our results indicate that ToCLEC3B is a constitutive and inducible acute-phase immune factor in the host's innate immune response of T. ovatus.

Antifungal immunity mediated by C-type lectin receptors may be a novel target in immunotherapy for urothelial bladder cancer.

Immunotherapies, such as immune-checkpoint blockade and adoptive T-cell therapy, offer novel treatment options with good efficacy for patients with urothelial bladder cancer. However, heterogeneity and therapeutic resistance have limited the use of immunotherapy. Further research into immune-regulatory mechanisms in bladder cancer is urgently required. Emerging evidence demonstrates that the commensal microbiota and its interactions with host immunity play pivotal roles in a variety of physiological and pathological processes, including in cancer. The gut microbiota has been identified as a potentially effective target of treatment that can be synergized with immunotherapy. The urothelial tract is also a key site for multiple microbes, although the immune-regulatory role of the urinary microbiome in the process of carcinogenesis of bladder cancer remains to be elucidated. We performed a comprehensive analysis of the expression and biological functions of C-type lectin receptors (CLRs), which have been recognized as innate pathogen-associated receptors for fungal microbiota, in bladder cancer. In line with previous research on fungal colonization of the urothelial tract, we found that CLRs, including Dectin-1, Dectin-2, Dectin-3, and macrophage-inducible Ca2+-dependent lectin receptor (Mincle), had a significant association with immune infiltration in bladder cancer. Multiple innate and adaptive pathways are positively correlated with the upregulation of CLRs. In addition, we found a significant correlation between the expression of CLRs and a range of immune-checkpoint proteins in bladder cancer. Based on previous studies and our findings, we hypothesize that the urinary mycobiome plays a key role in the pathogenesis of bladder cancer and call for more research on CLR-mediated anti-fungal immunity against bladder cancer as a novel target for immunotherapy in urothelial bladder cancer.

Innate/Inflammatory Bioregulation of Surfactant Protein D Alleviates Rat Osteoarthritis by Inhibiting Toll-Like Receptor 4 Signaling.

Osteoarthritis (OA) is a deteriorating disease of cartilage tissues mainly characterized as low-grade inflammation of the joint. Innate immune molecule surfactant protein D (SP-D) is a member of collectin family of collagenous Ca2+-dependent defense lectins and plays a vital role in the inflammatory and innate immune responses. The present study investigated the SP-D-mediated innate/inflammatory bioregulation in OA and explored the underlying molecular mechanism. Transcriptome analysis revealed that SP-D regulated genes were strongly enriched in the inflammatory response, immune response, cellular response to lipopolysaccharide (LPS), PI3K-Akt signaling, Toll-like receptor (TLR) signaling, and extracellular matrix (ECM)-receptor interaction pathways. Knockdown of the SP-D gene by the recombinant adeno-associated virus promoted the macrophage specific markers of CD68, F4/80 and TLR4 in the articular cartilage in vivo. SP-D alleviated the infiltration of synovial macrophages and neutrophils, and inhibited TLR4, TNF-α and the phosphorylation of PI3K, Akt and NF-κB p65 in cartilage. SP-D suppressed cartilage degeneration, inflammatory and immune responses in the rat OA model, whilst TAK-242 strengthened this improvement. In in vitro conditions, SP-D pre-treatment inhibited LPS-induced overproduction of inflammation-correlated cytokines such as IL-1β and TNF-α, and suppressed the overexpression of TLR4, MD-2 and NLRP3. SP-D prevented the LPS-induced degradation of ECM by down-regulating MMP-13 and up-regulating collagen II. Blocking of TLR4 by TAK-242 further enhanced these manifestations. We also demonstrated that SP-D binds to the TLR4/MD-2 complex to suppress TLR4-mediated PI3K/Akt and NF-κB signaling activation in chondrocytes. Taken together, these findings indicate that SP-D has chondroprotective properties dependent on TLR4-mediated PI3K/Akt and NF-κB signaling and that SP-D has an optimal bioregulatory effect on the inflammatory and innate responses in OA.

Targeting undruggable carbohydrate recognition sites through focused fragment library design

Carbohydrate-protein interactions are key for cell-cell and host-pathogen recognition and thus, emerged as viable therapeutic targets. However, their hydrophilic nature poses major limitations to the conventional development of drug-like inhibitors. To address this shortcoming, four fragment libraries were screened to identify metal-binding pharmacophores (MBPs) as novel scaffolds for inhibition of Ca2+-dependent carbohydrate-protein interactions. Here, we show the effect of MBPs on the clinically relevant lectins DC-SIGN, Langerin, LecA and LecB. Detailed structural and biochemical investigations revealed the specificity of MBPs for different Ca2+-dependent lectins. Exploring the structure-activity relationships of several fragments uncovered the functional groups in the MBPs suitable for modification to further improve lectin binding and selectivity. Selected inhibitors bound efficiently to DC-SIGN-expressing cells. Altogether, the discovery of MBPs as a promising class of Ca2+-dependent lectin inhibitors creates a foundation for fragment-based ligand design for future drug discovery campaigns.

The Protective Action of Piperlongumine Against Mycobacterial Pulmonary Tuberculosis in Its Mitigation of Inflammation and Macrophage Infiltration in Male BALB/c Mice.

IntroductionPiperlongumine (PL) is a bioactive alkaloid and medicinal compound of piperamide isolated from the long pepper (Piper longum Linn). It has demonstrated bactericidal action against Mycobacterium tuberculosis (MTB), the cause of pulmonary tuberculosis; nevertheless, immunomodulatory activity had not been identified for it in MTB-triggered granulomatous inflammation. This study investigated if piperlongumine could inhibit such inflammation.Material and MethodsMycobacterium tuberculosis strain H37Rv was subjected to a broth microdilution assay. Piperlongumine at 5, 15, and 25 μg/mL, 0.2% dimethyl sulphoxide as control or 4 μM of dexamethasone were tested in vitro on MH-S murine alveolar macrophages. BALB/c mice were orally administered PL at 50, 100 and 150 mg/kg b.w. after trehalose-6,6-dimycolate (TDM) stimulation. Chemokine and cytokine concentrations were determined in lung supernatants. Flow cytometry and Western blot analysis were performed to determine phosphorylated spleen tyrosine kinase (Syk), c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) pathways.ResultsPiperlongumine inhibited inflammatory mediators and adherence of lymphocyte function-associated antigen 1 to MH-S cells following TDM activation. It also improved macrophage clearance of MTB. In TDM-stimulated MH-S cells, PL significantly influenced the macrophage inducible Ca2+-dependent lectin receptor (Mincle)-Syk-ERK signalling pathway. Oral dosing of PL effectively suppressed the development of pulmonary granulomas and inflammatory reactions in the TDM-elicited mouse granuloma model.ConclusionPL as an inhibitor of MTB-triggered granulomatous inflammation may be an effective complementary treatment for mycobacterial infection.

A Simple Strategy to Obtain Synthetic Ca2+‐Dependent Lectin Mimics

AbstractMany lectins require a Ca2+ ion as structure directing co‐factor to function as carbohydrate binders. Such lectins are implicated in various important biological processes such as inflammation and infection, yet a simple strategy to mimic their function is lacking. Herein, a very simple dipyridyl ligand (6) is reported that can organize around a Pd2+ ion to form the ring‐like complexes [PdCl26] and [Pd62]2+. In CD2Cl2 with 5 % dmso‐d6, ligand 6 does not associate with glycosides, while its Pd2+ complexes selectively bind to β‐n‐octyl‐glycosides over α‐n‐octyl‐glycosides. The highest affinity (Ka1:1≈116 M−1) was found between the dicationic [Pd62]2+ and n‐octyl‐β‐D‐galactoside. Molecular modelling suggests a common binding motif with an important role of C−H⋅⋅⋅π interactions and two charge assisted bifurcated [N−H/C−H]+⋅⋅⋅O hydrogen bonds. Ligand 6 and its metal complexes thus provide a proof‐of‐concept for a very simple strategy to mimicking Ca2+‐dependent lectins.

Structural Basis of Dystroglycan Function and the Pathogenesis of Muscular Dystrophy

Dystroglycan (DG) is a widely expressed high-affinity extracellular matrix receptor that requires extensive glycosylation and additional post-translational processing. In skeletal muscle, DG is part of the dystrophin-glycoprotein complex, which is embedded in the plasma membrane and establishes a continuous link between laminin-G-like (LG) domains of extracellular matrix-resident proteins (laminin, agrin, and perlecan) and the cytoskeleton. Extracellular matrix proteins that contain LG domains bind to α-DG via a novel heteropolysaccharide [-GlcA-β1,3-Xyl-α1,3-]n called matriglycan, which is synthesized by the bifunctional enzyme known as Like-acetylglucosaminyltransferase (LARGE). Abnormalities in the post-translational processing of DG lead to an absence or reduction of the matriglycan modification on α-DG, and thereby lead to various forms of glycosylation-deficient muscular dystrophy (secondary dystroglycanopathies). We have used a multidisciplinary approach to provide the first atomic-level insights into the structure of a unique protein-carbohydrate interaction that is essential for the binding of α-DG to the extracellular matrix and proper skeletal muscle function. We first purified LARGE and synthesized matriglycan chains of defined lengths in sufficient quantities to perform both biochemical and structural studies. Using NMR spectroscopy, we found that matriglycan bound to laminin-α2 LG4,5 with high affinity (KD=0.23 µM) and that this binding was calcium dependent. Next, we initiated a collaboration with Erhard Hohenester, who had previously crystallized laminin-α2 LG4,5. Dr. Hohenester soaked matriglycan into crystals of LG4,5 to produce a high-resolution crystal structure of LG4,5 bound to matriglycan. This analysis revealed that the LG4 domain is a Ca2+-dependent lectin with specificity for GlcA-β1,3-Xyl disaccharides, and that a single glucuronic acid-β1,3-xylose disaccharide repeat straddles a Ca2+ ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca2+-bound water molecules. This chelating binding mode is unprecedented among animal lectins and accounts for the high affinity of this protein-carbohydrate interaction. Finally, we used two novel exoglycosidases to provide direct evidence that native α-DG contains unmodified matriglycan and numerous GlcA-Xyl repeats. The multiple tandem repeats in matriglycan are predicted to increase the apparent affinity of the protein for LG domains by favoring rapid rebinding after dissociation. Our results represent a major conceptual advancement regarding a functional carbohydrate and shed light on the mechanism of protein-carbohydrate interactions underlying dystroglycanopathies.

Particular Authoritative of N-acetylglucosamine to the Chicken Hepatic Lectin

Among Ca2+-dependent (C-type) creature lectins, the chicken hepatic lectin (CHL) is special in showing nearly total selectivity for N-acetylglucosamine over other monosaccharide ligands. The gem structures of the carbohydrate-recognition space (CRD) from serum mannose-binding protein (MBP) and of a complex between the CRD from liver MBP and the methyl glycoside of N-acetylglucosamine were utilized to show the official location in CHL. Substitution of parcels of CHL into the MBP system did not considerably increment selectivity. A bacterial expression framework for the CRD of CHL was created so that particular buildups anticipated to be close the 2-acetamido substituent of N-acetylglucosamine might be changed by site-directed mutagenesis. The comes about indicate that the ligand is bound to CHL within the same introduction because it ties to liver MBP. A tyrosine and a valine buildup that likely contact the the N-acetyl bunch have been recognized.

Abstract B03: Immunotherapy of ovarian cancer with glycomimetic peptides

Abstract Successful strategies for treating women with ovarian cancer remain elusive. Whereas chemotherapy with drugs such as paclitaxel and carboplatin extends survival, it bears a significant cost in toxicity. Immunotherapies with antibodies such as anti-PD-1, anti-PD-L1, or anti-VEGF have been successful in a fraction of patients. Inhibitors of poly(ADP-ribose) polymerase (PARP) have gained interest, particularly for the minority of patients who carry the BRCA-1/2 mutations. Ovarian cancer is highly inflammatory and recent reports described recruitment of monocytes, which then differentiate into a unique subset of dendritic cells (DCs) within the inflamed ascites environment. These monocyte-derived DCs (mo-DCs) have the potential to activate cytotoxic CD8+ T cells that attack tumor cells, but progression of disease is not abrogated without additional stimuli. We hypothesize that a means to actuate this role of mo-DCs will be an important component of a successful treatment of inflammatory tumors such as ovarian ascites. Mo-DCs along with CD1c+ DC2 subtypes express CD301, the Ca2+-dependent lectin domain family 10 member A (CLEC10A), which is a pathogen-recognition receptor specific for binding the ligand N-acetylgalactoasmine (GalNAc). A series of experiments were designed to test whether a novel peptide mimetic of GalNAc, designated sv6D, can enhance anticancer immune activity and limit the progression of ovarian cancer. CLEC10A is a type II transmembrane receptor that initiates a Ca2+ signal upon binding of sv6D and subsequent endocytosis. Production of IFN-γ by naïve T cells occurred when cultured with in vitro generated mo-DCs, which are similar to mo-DCs induced by inflammation, and 10 nM sv6D. In a syngeneic, orthotopic murine model of ovarian cancer, doses of 0.1 nmole/g of sv6D on alternate days completely suppressed ascites accumulation for several weeks, a measure of inhibition of tumor progression. Survival was also extended when sv6D was administered to mice previously treated with paclitaxel. Although treatment with anti-PD-1 was ineffective, i.p. injections of anti-PD-1 in combination with a tolerance-inducing treatment with sv6D provided maximal survival. Our studies demonstrate that 1) sv6D stimulates proliferation and differentiation of immune cells in the peritoneal cavity and serves as a trigger to promote the activation of CD8+ T cells by mo-DCs in ovarian ascites, 2) sv6D as a single agent inhibits progression of ovarian cancer and enhances survival in a mouse model of ovarian cancer, 3) sv6D in combination with paclitaxel or anti-PD-1 extends survival beyond that of either agent alone, and 4) sv6D is not antigenic and treatment with the peptide was not associated with evident toxicity. Taken together, these data demonstrate the potential for this novel approach of harnessing lectin receptors as a means toward an effective ovarian cancer treatment. Citation Format: Laura L. Eggink, J. Kenneth Hoober. Immunotherapy of ovarian cancer with glycomimetic peptides [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B03.

Structural Basis of Dystroglycan Function and the Pathogenesis of Muscular Dystrophy

(DG) is a widely expressed high‐affinity extracellular matrix receptor that requires extensive glycosylation and additional post‐translational processing. In skeletal muscle, DG is part of the dystrophin‐glycoprotein complex, which establishes a continuous link between laminin‐G‐like (LG) domains of extracellular matrix‐resident proteins (laminin, agrin, and perlecan) and the cytoskeleton. Extracellular matrix proteins that contain LG domains bind to α‐DG via a novel heteropolysaccharide [‐GlcA‐β1,3‐Xyl‐α1,3‐]n called matriglycan, which is synthesized by the bifunctional enzyme known as Like‐acetylglucosaminyltransferase (LARGE). We have used a multidisciplinary approach to provide the first atomic‐level insights into the structure of a unique protein‐carbohydrate interaction that is essential for the binding of α‐DG to the extracellular matrix. We first purified LARGE and synthesized matriglycan chains of defined lengths in sufficient quantities to perform both biochemical and structural studies. Using NMR spectroscopy, we found that matriglycan bound to laminin‐α2 LG4,5 with high affinity (Kd=0.23 μM) and that this binding was calcium dependent. Next, we initiated a collaboration with Erhard Hohenester, who had previously crystallized laminin‐α2 LG4,5. We provided Dr. Hohenester with enough matriglycan to soak into crystals of LG4,5 and to produce a high‐resolution crystal structure of LG4,5 bound to matriglycan. This analysis revealed that the LG4 domain is a Ca2+‐dependent lectin with specificity for GlcA‐β1,3‐Xyl disaccharides, and that a single glucuronic acid‐β1,3‐xylose disaccharide repeat straddles a Ca2+ ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca2+‐bound water molecules. This chelating binding mode is unprecedented among animal lectins and accounts for the high affinity of this protein‐carbohydrate interaction as measured by NMR. Finally, we used two novel exoglycosidases to provide direct evidence that native α‐DG contains unmodified matriglycan and numerous GlcA‐Xyl repeats. The multiple tandem repeats in matriglycan are predicted to increase the apparent affinity of the protein for LG domains by favoring rapid rebinding after dissociation. Abnormalities in the post‐translational processing of DG lead to an absence or reduction of the matriglycan modification on α‐DG, and thereby lead to various forms of muscular dystrophy (secondary dystroglycanopathies). Our results represent a major conceptual advancement regarding a functional carbohydrate and shed light on the mechanism of protein‐carbohydrate interactions.Support or Funding InformationDr. Campbell is an investigator of the Howard Hughes Medical Institute. This work was supported in part by a Paul D. Wellstone Muscular Dystrophy Cooperative Research Center grant.

Characterization of Macrophage Galactose-type Lectin (MGL) ligands in colorectal cancer cell lines

BackgroundThe Ca2+-dependent C-type lectin receptor Macrophage Galactose-type Lectin (MGL) is highly expressed by tolerogenic dendritic cells (DC) and macrophages. MGL exhibits a high binding specificity for terminal alpha- and beta-linked GalNAc residues found in Tn, sTn and LacdiNAc antigens. These glycan epitopes are often overexpressed in colorectal cancer (CRC), and, as such, MGL can be used to discriminate tumor from the corresponding healthy tissues. Moreover, the high expression of MGL ligands is associated with poor disease-free survival in stage III of CRC tumors. Nonetheless, the glycoproteins expressed by tumor cells that are recognized by MGL have hitherto remained elusive. MethodsUsing a panel of three CRC cell lines (HCT116, HT29 and LS174T), recapitulating CRC diversity, we performed FACS staining and pull-down assays using a recombinant soluble form of MGL (and a mutant MGL as control) combined with mass spectrometry-based (glyco)proteomics. ResultsHCT116 and HT29, but not LS174T, are high MGL-binding CRC cell lines. On these cells, the major cell surface binding proteins are receptors (e.g. MET, PTK7, SORL1, PTPRF) and integrins (ITGB1, ITGA3). From these proteins, several N- and/or O-glycopeptides were identified, of which some carried either a LacdiNAc or Tn epitope. ConclusionsWe have identified cell surface MGL-ligands on CRC cell lines. General significanceAdvances in (glyco)proteomics have led to identification of candidate key mediators of immune-evasion and tumor growth in CRC.

Galactose-Specific, Hemolytic Lectin CEL-III from Cucumaria echinata.

CEL-III is a Ca2+-dependent and galactose-specific lectin purified from the sea cucumber, Cucumaria echinata; it exhibits hemolytic and hemagglutinating activities. CEL-III consists of the following three distinct domains: two N-terminal carbohydrate-binding domains (1 and 2), which adopt β-trefoil folds such as the B-chain of ricin and are members of the (QXW)3 motif family, and domain 3, an oligomerization domain. After binding to the cell surface carbohydrate chains through domains 1 and 2, domain 3 self-associates to form transmembrane pores composed of CEL-III heptamers, leading to cell lysis or death. In this chapter, the purification and carbohydrate-coated microplate binding assay of CEL-III are described.

Activation of C-Type Lectin Receptor and (RIG)-I-Like Receptors Contributes to Proinflammatory Response in Middle East Respiratory Syndrome Coronavirus-Infected Macrophages.

BackgroundHuman infection with Middle East respiratory syndrome coronavirus (MERS-CoV) poses an ongoing threat to public health worldwide. The studies of MERS patients with severe disease and experimentally infected animals showed that robust viral replication and intensive proinflammatory response in lung tissues contribute to high pathogenicity of MERS-CoV. We sought to identify pattern recognition receptor (PRR) signaling pathway(s) that mediates the inflammatory cascade in human macrophages upon MERS-CoV infection.MethodsThe potential signaling pathways were manipulated individually by pharmacological inhibition, small interfering ribonucleic acid (siRNA) depletion, and antibody blocking. The MERS-CoV-induced proinflammatory response was evaluated by measuring the expression levels of key cytokines and/or chemokines. Reverse transcription-quantitative polymerase chain reaction assay, flow cytometry analysis, and Western blotting were applied to evaluate the activation of related PRRs and engagement of adaptors.ResultsMERS-CoV replication significantly upregulated C-type lectin receptor (CLR) macrophage-inducible Ca2+-dependent lectin receptor (Mincle). The role of Mincle for MERS-CoV-triggered cytokine/chemokine induction was established based on the results of antibody blockage, siRNA depletion of Mincle and its adaptor spleen tyrosine kinase (Syk), and Syk pharmacological inhibition. The cytokine and/or chemokine induction was significantly attenuated by siRNA depletion of retinoic acid-inducible-I-like receptors (RLR) or adaptor, indicating that RLR signaling also contributed to MERS-CoV-induced proinflammatory response.ConclusionsThe CLR and RLR pathways are activated and contribute to the proinflammatory response in MERS-CoV-infected macrophages.

Oral delivery of pancreatitis-associated protein by Lactococcus lactis displays protective effects in dinitro-benzenesulfonic-acid-induced colitis model and is able to modulate the composition of the microbiota.

SummaryAntimicrobial peptides secreted by intestinal immune and epithelial cells are important effectors of innate immunity. They play an essential role in the maintenance of intestinal homeostasis by limiting microbial epithelium interactions and preventing unnecessary microbe‐driven inflammation. Pancreatitis‐associated protein (PAP) belongs to Regenerating islet‐derived III proteins family and is a C‐type (Ca+2 dependent) lectin. PAP protein plays a protective effect presenting anti‐inflammatory properties able to reduce the severity of colitis, preserving gut barrier and epithelial inflammation. Here, we sought to determine whether PAP delivered at intestinal lumen by recombinant Lactococcus lactis strain (LL‐PAP) before and after chemically induced colitis is able to reduce the severity in two models of colitis. After construction and characterization of our recombinant strains, we tested their effects in dinitro‐benzenesulfonic‐acid (DNBS) and Dextran sulfate sodium (DSS) colitis model. After the DNBS challenge, mice treated with LL‐PAP presented less severe colitis compared with PBS and LL‐empty‐treated mice groups. After the DSS challenge, no protective effects of LL‐PAP could be detected. We determined that after 5 days administration, LL‐PAP increase butyrate producer's bacteria, especially Eubacterium plexicaudatum. Based on our findings, we hypothesize that a treatment with LL‐PAP shifts the microbiota preventing the severity of colon inflammation in DNBS colitis model. These protective roles of LL‐PAP in DNBS colitis model might be through intestinal microbiota modulation.