The glycan ligands recognized by Siglecs, influenza viruses, and galectins, as well as many plant lectins, are not well defined. To explore their binding to asparagine (Asn)-linked N-glycans, we synthesized a library of isomeric multiantennary N-glycans that vary in terminal non-reducing sialic acid, galactose, and N-acetylglucosamine residues, as well as core fucose. We identified specific recognition of N-glycans by several plant lectins, human galectins, influenza viruses, and Siglecs, and explored the influence of sialic acid linkages and branching of the N-glycans. These results show the unique recognition of complex-type N-glycans by a wide variety of glycan-binding proteins and their abilities to distinguish isomeric structures, which provides new insights into the biological roles of these proteins and the uses of lectins in biological applications to identify glycans.
Glycans in polysaccharides and glycoconjugates of the hydrophilic exterior of all animal cells participate in signal transduction, cellular adhesion, intercellular signaling, and sites for binding of pathogens largely through protein-glycan interactions. Microarrays of defined glycans have been used to study the binding specificities of biologically relevant glycan-binding proteins (GBP), but such arrays are limited by their lack of diversity or relevance to the GBP being investigated. Shotgun glycan microarrays are made up of structurally undefined glycans that were released from natural sources, labeled with bifunctional reagents so that they can be monitored during their purification using multidimensional chromatographic procedures, stored as a tagged glycan library (TGL) and subsequently printed onto microarrays at equal molar concentrations. The shotgun glycan microarray is then interrogated with a biologically relevant GBP and the corresponding glycan ligands can be retrieved from the TGL for detailed structural analysis and further functional analysis. Shotgun glycomics extended the defined glycan microarray to a discovery platform that supports functional glycomic analyses and may provide a useful process for ultimately defining the human glycome.
Traditional glycan microarray data is typically presented as excel files with limited visualization and interactivity. Thus, comparisons and analysis of glycan array data have been difficult, and there is need for a tool to facilitate data mining of glycan array data.
GLAD (GLycan Array Dashboard) is a web-based tool to visualize, analyze, present, and mine glycan microarray data. GLAD allows users to input multiple data files to create comparisons. GLAD extends the capability of the microarray data to produce more comparative visualizations in the form of grouped bar charts, heatmaps, calendar heatmaps, force graphs and correlation maps in order to analyze broad sets of samples. Additionally, it allows users to filter, sort and normalize the data and view glycan structures in an interactive manner, to facilitate faster visual data mining.
Exposure to Mycobacterium tuberculosis (Mtb) results in heterogeneous clinical outcomes including primary progressive tuberculosis and latent Mtb infection (LTBI). Mtb infection is identified using the tuberculin skin test and interferon-γ (IFN-γ) release assay IGRA, and a positive result may prompt chemoprophylaxis to prevent progression to tuberculosis. In the present study, we report on a cohort of Ugandan individuals who were household contacts of patients with TB. These individuals were highly exposed to Mtb but tested negative disease by IFN-γ release assay and tuberculin skin test, 'resisting' development of classic LTBI. We show that 'resisters' possess IgM, class-switched IgG antibody responses and non-IFN-γ T cell responses to the Mtb-specific proteins ESAT6 and CFP10, immunologic evidence of exposure to Mtb. Compared to subjects with classic LTBI, 'resisters' display enhanced antibody avidity and distinct Mtb-specific IgG Fc profiles. These data reveal a distinctive adaptive immune profile among Mtb-exposed subjects, supporting an expanded definition of the host response to Mtb exposure, with implications for public health and the design of clinical trials.
Despite advances in stem cell research, cell transplantation therapy for liver failure is impeded by a shortage of human primary hepatocytes (HPH), along with current differentiation protocol limitations. Several studies have examined the concept of co-culture of human induced pluripotent cells (hiPSCs) with various types of supporting non-parenchymal cells to attain a higher differentiation yield and to improve hepatocyte-like cell functions both in vitro and in vivo. Co-culturing hiPSCs with human endothelial cells (hECs) is a relatively new technique that requires more detailed studies. Using our 3D human embryoid bodies (hEBs) formation technology, we interlaced Human Adipose Microvascular Endothelial Cells (HAMEC) with hiPSCs, leading to a higher differentiation yield and notable improvements across a wide range of hepatic functions. We conducted a comprehensive gene and protein secretion analysis of our HLCs coagulation factors profile, showing promising results in comparison with HPH. Furthermore, a stage-specific glycomic analysis revealed that the differentiated hepatocyte-like clusters (HLCs) resemble the glycan features of a mature tissue rather than cells in culture. We tested our HLCs in animal models, where the presence of HAMEC in the clusters showed a consistently better performance compared to the hiPSCs only group in regard to persistent albumin secretion post-transplantation.
To assess the effects of walnuts on cardiometabolic outcomes in obese subjects and to explore underlying mechanisms using novel methods including metabolomic, lipidomic, glycomic, and microbiome analysis integrated with lipid particle fractionation, appetite-regulating hormones and hemodynamic measurements.
MATERIALS AND METHODS:
10 obese subjects were enrolled in this cross-over, randomized, double-blind, placebo-controlled clinical trial. Patients participated in two 5-day inpatient stays during which they consumed a smoothie containing 48g walnuts or a macronutrient-matched placebo smoothie without nuts, with a one-month washout period between the two visits.
Walnut consumption improved aspects of the lipid profile, i.e. reduced fasting small and dense LDL particles (p<.02) and increased postprandial large HDL particles (p<.01). Lipoprotein Insulin Resistance Score, glucose and insulin AUC decreased significantly after walnut consumption (p<.01, p<.02, p<.04, respectively). Consuming walnuts significantly increased 10 N-glycans, with 8 of them carrying a fucose core. Lipidomic analysis showed a robust reduction in harmful ceramides, hexosylceramides and sphingomyelins, which have been shown to mediate effects on cardiometabolic risk. Peptide YY AUC significantly increased after walnut consumption (p<.03). No major significant changes in hemodynamic, metabolomic analysis or in host health-promoting bacteria such as Faecalibacterium were found.
These data provide a more comprehensive mechanistic perspective of the effect of dietary walnut consumption on cardiometabolic parameters. Lipidomic and lipid nuclear magnetic resonance spectroscopy analysis showed an early but significant reduction in ceramides and other atherogenic lipids with walnut consumption that may explain the longer-term benefits of walnuts on insulin resistance, cardiovascular risk and mortality. This article is protected by copyright. All rights reserved.
High levels of proinflammatory cytokines have been associated with a loss of tissue function in ocular autoimmune diseases, but the basis for this relationship remains poorly understood. Here we investigate a new role for tumor necrosis factor α in promoting N-glycan-processing deficiency at the surface of the eye through inhibition of N-acetylglucosaminyltransferase expression in the Golgi. Using mass spectrometry, complex-type biantennary oligosaccharides were identified as major N-glycan structures in differentiated human corneal epithelial cells. Remarkably, significant differences were detected between the efficacies of cytokines in regulating the expression of glycogenes involved in the biosynthesis of N-glycans. Tumor necrosis factor α but not IL-1β had a profound effect in suppressing the expression of enzymes involved in the Golgi branching pathway, including N-acetylglucosaminyltransferases 1 and 2, which are required for the formation of biantennary structures. This decrease in gene expression was correlated with a reduction in enzymatic activity and impaired N-glycan branching. Moreover, patients with ocular mucous membrane pemphigoid were characterized by marginal N-acetylglucosaminyltransferase expression and decreased N-glycan branching in the conjunctiva. Together, these data indicate that proinflammatory cytokines differentially influence the expression of N-glycan-processing enzymes in the Golgi and set the stage for future studies to explore the pathophysiology of ocular autoimmune diseases.
OBJECTIVE: To better understand the role of B cells, the potential mechanisms responsible for their aberrant activation, and the production of autoantibodies in the pathogenesis of Sjögren's syndrome (SS), this study explored patterns of selection pressure and sites of N-glycosylation acquired by somatic mutation (acN-glyc) in the IgG variable (V) regions of antibody-secreting cells (ASCs) isolated from the minor salivary glands of patients with SS and non-SS control patients with sicca symptoms.
METHODS: A novel method to produce and characterize recombinant monoclonal antibodies (mAb) from single cell-sorted ASC infiltrates was applied to concurrently probe expressed genes (all heavy- and light-chain isotypes as well as any other gene of interest not related to immunoglobulin) in the labial salivary glands of patients with SS and non-SS controls. V regions were amplified by reverse transcription-polymerase chain reaction, sequenced, and analyzed for the incidence of N-glycosylation and selection pressure. For specificity testing, the amplified regions were expressed as either the native mAb or mutant mAb lacking the acN-glyc motif. Protein modeling was used to demonstrate how even an acN-glyc site outside of the complementarity-determining region could participate in, or inhibit, antigen binding.
RESULTS: V-region sequence analyses revealed clonal expansions and evidence of secondary light-chain editing and allelic inclusion, of which neither of the latter two have previously been reported in patients with SS. Increased frequencies of acN-glyc were found in the sequences from patients with SS, and these acN-glyc regions were associated with an increased number of replacement mutations and lowered selection pressure. A clonal set of polyreactive mAb with differential framework region 1 acN-glyc motifs was also identified, and removal of the acN-glyc could nearly abolish binding to autoantigens.
CONCLUSION: These findings support the notion of an alternative mechanism for the selection and proliferation of some autoreactive B cells, involving V-region N-glycosylation, in patients with SS.
F-type lectins are phylogenetically widespread but selectively distributed fucose-binding lectins with L-fucose- and calcium-binding sequence motifs and an F-type lectin fold. Bacterial F-type lectin domains frequently occur in tandem with various protein domains in diverse architectures, indicating a possible role in directing enzyme activities or other biological functions to distinct fucosylated niches. Here, we report the biochemical characterization of a Streptosporangium roseum protein containing an F-type lectin domain in tandem with an NPCBM-associated domain and a family GH 29A alpha-l-fucosidase domain. We show that the F-type lectin domain of this protein recognizes fucosylated glycans in both α and β linkages but has high affinity for a Fuc-α-1,2-Gal motif and that the alpha-l-fucosidase domain displays hydrolytic activity on glycan substrates with α1-2 and α1-4 linked fucose. We also show that the F-type lectin domain does not have any effect on the activity of the cis-positioned alpha-l-fucosidase domain with the synthetic substrate, 4-Methylumbelliferyl-alpha-l-fucopyranoside or on inhibition of this activity by l-fucose or deoxyfuconojirimycin hydrochloride. However, the F-type lectin domain together with the NPCBM-associated domain enhances the activity of the cis-positioned alpha-l-fucosidase domain for soluble fucosylated oligosaccharide substrates. While there are many reports of glycoside hydrolase activity towards insoluble and soluble polysaccharides being enhanced by cis-positioned carbohydrate binding modules on the polypeptide, this is the first report, to our knowledge, of enhancement of activity towards aqueous, freely diffusible, small oligosaccharides. We propose a model involving structural stabilization and a bind-and-jump action mediated by the F-type lectin domain to rationalize our findings.
Rotaviruses (RVs), which cause severe gastroenteritis in infants and children, recognize glycan ligands in a genotype-dependent manner via the distal VP8* head of the spike protein VP4. However, the glycan binding mechanisms remain elusive for the P[II] genogroup RVs, including the widely prevalent human RVs (P, P, and P) and a rare P RV. In this study, we characterized the glycan binding specificities of human and porcine P/P RV VP8*s and found that the P[II] genogroup RV VP8*s could commonly interact with mucin core 2, which may play an important role in RV evolution and cross-species transmission. We determined the first P VP8* structure, as well as the complex structures of human P VP8*, with core 2 and lacto--tetraose (LNT). A glycan binding site was identified in human P VP8*. Structural superimposition and sequence alignment revealed the conservation of the glycan binding site in the P[II] genogroup RV VP8*s. Our data provide significant insight into the glycan binding specificity and glycan binding mechanism of the P[II] genogroup RV VP8*s, which could help in understanding RV evolution, transmission, and epidemiology and in vaccine development. Rotaviruses (RVs), belonging to the family , are double-stranded RNA viruses that cause acute gastroenteritis in children and animals worldwide. Depending on the phylogeny of the VP8* sequences, P and P RVs are grouped into genogroup II, together with P and P, which are widely prevalent in humans. In this study, we characterized the glycan binding specificities of human and porcine P/P RV VP8*s, determined the crystal structure of P VP8*, and uncovered the glycan binding pattern in P VP8*, revealing a conserved glycan binding site in the VP8*s of P[II] genogroup RVs by structural superimposition and sequence alignment. Our data suggested that mucin core 2 may play an important role in P[II] RV evolution and cross-species transmission. These data provide insight into the cell attachment, infection, epidemiology, and evolution of P[II] genogroup RVs, which could help in developing control and prevention strategies against RVs.
Group/species C rotaviruses (RVCs) have been identified as important pathogens of acute gastroenteritis (AGE) in children, family-based outbreaks, as well as animal infections. However, little is known regarding their host-specific interaction, infection, and pathogenesis. In this study, we performed serial studies to characterize the function and structural features of a human G4P RVC VP8* that is responsible for the host receptor interaction. Glycan microarrays demonstrated that the human RVC VP8* recognizes type A histo-blood group antigens (HBGAs), which was confirmed by synthetic glycan-/saliva-based binding assays and hemagglutination of red blood cells, establishing a paradigm of RVC VP8*-glycan interactions. Furthermore, the high-resolution crystal structure of the human RVC VP8* was solved, showing a typical galectin-like structure consisting of two β-sheets but with significant differences from cogent proteins of group A rotaviruses (RVAs). The VP8* in complex with a type A trisaccharide displays a novel ligand binding site that consists of a particular set of amino acid residues of the C-D, G-H, and K-L loops. RVC VP8* interacts with type A HBGAs through a unique mechanism compared with that used by RVAs. Our findings shed light on the host-virus interaction and the coevolution of RVCs and will facilitate the development of specific antivirals and vaccines. Group/species C rotaviruses (RVCs), members of family, infect both humans and animals, but our knowledge about the host factors that control host susceptibility and specificity is rudimentary. In this work, we characterized the glycan binding specificity and structural basis of a human RVC that recognizes type A HBGAs. We found that human RVC VP8*, the rotavirus host ligand binding domain that shares only ∼15% homology with the VP8* domains of RVAs, recognizes type A HBGA at an as-yet-unknown glycan binding site through a mechanism distinct from that used by RVAs. Our new advancements provide insights into RVC-cell attachment, the critical step of virus infection, which will in turn help the development of control and prevention strategies against RVs.
Individual lectin-carbohydrate interactions are usually of low affinity. However, high avidity is frequently attained by the multivalent presentation of glycans on biological surfaces coupled with the occurrence of high order lectin oligomers or tandem repeats of lectin domains in the polypeptide. F-type lectins are l-fucose binding lectins with a typical sequence motif, HX(26)RXDX(4)R/K, whose residues participate in l-fucose binding. We previously reported the presence of a few eukaryotic F-type lectin domains with partial sequence duplication that results in the presence of two l-fucose-binding sequence motifs. We hypothesized that such partial sequence duplication would result in greater avidity of lectin-ligand interactions. Inspired by this example from Nature, we attempted to engineer a bacterial F-type lectin domain from Streptosporangium roseum to attain avid binding by mimicking partial duplication. The engineered lectin demonstrated 12-fold greater binding strength than the wild-type lectin to multivalent fucosylated glycoconjugates. However, the affinity to the monosaccharide l-fucose in solution was similar and partial sequence duplication did not result in an additional functional l-fucose binding site. We also cloned, expressed and purified a Branchiostoma floridae F-type lectin domain with naturally occurring partial sequence duplication and confirmed that the duplicated region with the F-type lectin sequence motif did not participate in l-fucose binding. We found that the greater binding strength of the engineered lectin from S. roseum was instead due to increased oligomerization. We believe that this Nature-inspired strategy might be useful for engineering lectins to improve binding strength in various applications.
Plant lectins are gaining interest because of their interesting biological properties. Several Adenia species, that are being used in traditional medicine to treat many health ailments have shown presence of lectins or carbohydrate binding proteins. Here, we report the purification, characterization and biological significance of N-Acetyl galactosamine specific lectin from Adenia hondala (AHL) from Passifloraceae family. AHL was purified in a single step by affinity chromatography on asialofetuin Sepharose 4B column, characterized and its fine sugar specificity determined by glycan array analysis. AHL is human blood group non specific and also agglutinates rabbit erythrocytes. AHL is a glycoprotein with 12.5% of the carbohydrate, SDS-PAGE, MALDI-TOF-MS and ESI-MS analysis showed that AHL is a monomer of 31.6 kDa. AHL is devoid of DNase activity unlike other Ribosome inactivating proteins (RIPs). Glycan array analysis of AHL revealed its highest affinity for terminal lactosamine or polylactosamine of N- glycans, known to be over expressed in hepatocellular carcinoma and colon cancer. AHL showed strong binding to human hepatocellular carcinoma HepG2 cells with MFI of 59.1 expressing these glycans which was effectively blocked by 93.1% by asialofetuin. AHL showed dose and time dependent growth inhibitory effects on HepG2 cells with IC of 4.8 μg/ml. AHL can be explored for its clinical potential.
Variable lymphocyte receptors (VLRs) are unconventional adaptive immune receptors relatively recently discovered in the phylogenetically ancient jawless vertebrates, lamprey and hagfish. VLRs bind antigens using a leucine-rich repeat fold and are the only known adaptive immune receptors that do not utilize an immunoglobulin fold for antigen recognition. While immunoglobulin antibodies have been studied extensively, there are comparatively few studies on antigen recognition by VLRs, particularly for protein antigens. Here we report isolation, functional and structural characterization of three VLRs that bind the protein toll-like receptor 5 (TLR5) from zebrafish. Two of the VLRs block binding of TLR5 to its cognate ligand flagellin in functional assays using reporter cells. Co-crystal structures revealed that these VLRs bind to two different epitopes on TLR5, both of which include regions involved in flagellin binding. Our work here demonstrates that the lamprey adaptive immune system can be used to generate high-affinity VLR clones that recognize different epitopes and differentially impact natural ligand binding to a protein antigen.
The Tn neoantigen (GalNAcα1-O-Ser/Thr) is an O-glycan expressed in various types of human cancers. Studies in several Tn-expressing cancer cell lines and pancreatic tumors have identified loss of Cosmc expression caused by either mutations or promoter hypermethylation. In this study, we explored the mechanism(s) for Tn expression in human colorectal cancers (CRC).
Tn-expressing cell populations were isolated from CRC cell lines by Fluorescence-associated cell sorting (FACS). The expression of the Tn and sialylated Tn (STn) antigens, Cosmc, T-synthase, and mucins was characterized in paired specimens with CRC and in CRC cell lines by immunostaining, western blot, and qPCR.
Using well-defined monoclonal antibodies, we confirmed prevalent Tn/STn expression in CRC samples. However, a majority of these tumors had elevated T-synthase activity and expression of both Cosmc and T-synthase proteins. Meanwhile, Tn antigen expression was not caused by mucin overproduction. In addition, we found that Tn-expressing CRC cell lines had either loss-of-function mutations in Cosmc or reversible Tn antigen expression, which was not caused by the deficiency of T-synthase activity.
Our results demonstrate multiple mechanisms for Tn expression in CRCs.
Sepsis is an overwhelming systemic inflammation resulting from an uncontrolled infection that causes extensive tissue damage, organ dysfunction and eventually death. A growing body of evidence indicates that impaired neutrophil migration to the site of infection is associated with poor outcome in sepsis. Here we show that galectin-3 (Gal-3), an endogenous glycan-binding protein, plays a critical role in sepsis outcome. We found that serum Gal-3 concentration increased in patients with septic shock and mice undergoing sepsis induced by cecal ligation and puncture (CLP). Mice deficient in Gal-3 (Gal-3 KO) are more resistant to sepsis induced by CLP, showing lower levels of biochemical markers and neutrophil infiltration for organ injury/dysfunction than those observed in wild-type mice (WT). Furthermore, Gal-3 KO mice show an increased number of neutrophils in the primary focus of infection and reduced bacterial loads in the peritoneal cavity, blood, and lungs. Mechanistically, blood neutrophils from septic mice show higher levels of surface-bound Gal-3 than neutrophils from naive mice. The deficiency of Gal-3 was associated with increased rolling and adhesion of these cells in mesenteric venules. Our results indicate that Gal-3, secreted during sepsis, inhibits neutrophil migration into the infectious focus, which promotes the bacterial spread and worsens the outcome of sepsis.
Germinal centers (GC) are microanatomical niches where B cells proliferate, undergo antibody affinity maturation, and differentiate to long-lived memory B cells and antibody-secreting plasma cells. For decades, GC B cells have been defined by their reactivity to the plant lectin peanut agglutinin (PNA), which binds serine/threonine (O-linked) glycans containing the asialylated disaccharide Gal-β1,3-GalNAc-Ser/Thr (also called T-antigen). In T cells, acquisition of PNA binding by activated T cells and thymocytes has been linked with altered tissue homing patterns, cell signaling, and survival. Yet, in GC B cells, the glycobiological basis and significance of PNA binding remains surprisingly unresolved. Here, we investigated the basis for PNA reactivity of GC B cells. We found that GC B cell binding to PNA is associated with downregulation of the α2,3 sialyltransferase, ST3GAL1 (ST3Gal1), and overexpression of ST3Gal1 was sufficient to reverse PNA binding in B cell lines. Moreover, we found that the primary scaffold for PNA-reactive O-glycans in B cells is the B cell receptor-associated receptor-type tyrosine phosphatase CD45, suggesting a role for altered O-glycosylation in antigen receptor signaling. Consistent with similar reports in T cells, ST3Gal1 overexpression in B cells in vitro induced drastic shortening in O-glycans, which we confirmed by both antibody staining and mass spectrometric O-glycomic analysis. Unexpectedly, ST3Gal1-induced changes in O-glycan length also correlated with altered binding of two glycosylation-sensitive CD45 antibodies, RA3-6B2 (more commonly called B220) and MEM55, which (in humans) have previously been reported to favor binding to naïve/GC subsets and memory/plasmablast subsets, respectively. Analysis of primary B cell binding to B220, MEM55, and several plant lectins suggested that B cell differentiation is accompanied by significant loss of O-glycan complexity, including loss of extended Core 2 O-glycans. To our surprise, decreased O-glycan length from naïve to post-GC fates best correlated not with ST3Gal1, but rather downregulation of the Core 2 branching enzyme GCNT1. Thus, our data suggest that O-glycan remodeling is a feature of B cell differentiation, dually regulated by ST3Gal1 and GCNT1, that ultimately results in expression of distinct O-glycosylation states/CD45 glycoforms at each stage of B cell differentiation.
Glycan-binding proteins (GBPs) play critical roles in diverse cellular functions such as cell adhesion, signal transduction and immune response. Studies of the interaction between GBPs and glycans have been hampered by the availability of high throughput and high-content technologies. Here we report multiplex glycan bead array (MGBA) that allows simultaneous analyses of 384 samples and up to 500 glycans in a single assay. The specificity, sensitivity and reproducibility of MGBA are evaluated using 39 plant lectins, 13 recombinant anti-glycan antibodies, and mammalian GBPs. We demonstrate the utility of this platform by the analyses of natural anti-glycan IgM and IgG antibodies in 961 human serum samples and the discovery of anti-glycan antibody biomarkers for ovarian cancer. Our data indicate that the MGBA platform is particularly suited for large population-based studies that require the analyses of large numbers of samples and glycans.
Cryptosporidium spp. are the causative agents of diarrheal disease worldwide, but effective treatments are lacking. Cryptosporidium employs mucin-like glycoproteins with O-glycans to attach to and infect host intestinal epithelial cells. The Tn antigen (GalNAcα1-Ser/Thr) is an O-glycan essential for these processes, as Tn-specific lectins and a Tn-specific monoclonal antibody block attachment to and infection of host cells in vitro. The enzymes in Cryptosporidium catalyzing their synthesis, however, have not been studied. Previously, we identified four genes encoding putative UDP N-acetyl-α-d-galactosamine:polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts) in the genomes of three Cryptosporidium spp. Here we report the in silico analysis, cloning, expression, purification, and characterization of one of the four enzymes Cryptosporidium parvum (Cp)-ppGalNAc-T4. This enzyme contains the characteristic domains and motifs conserved in ppGalNAc-Ts and is expressed at multiple time points during in vitro infection. Recombinant soluble Cp-ppGalNAc-T4 was enzymatically active against an unmodified EA2 peptide suggesting that it may function as an "initiating" ppGalNAc-T. Cp-ppGalNAc-T4 also exhibited a strong preference for UDP-GalNAc over other nucleotide sugar donors and was active against unmodified and O-glycosylated versions of the C. parvum gp40-derived peptide, with a preference for the former, suggesting it may play a role in modifying this glycoprotein in vivo. Given the importance of mucin-type O-glycosylation in Cryptosporidium spp., the enzymes that catalyze their synthesis may serve as potential therapeutic targets.
Selectins are a class of cell adhesion molecules that play a critical role during the initial steps of inflammation. The N-terminal domain of P-selectin glycoprotein ligand-1 (PSGL-1) binds to all selectins, but with the highest affinity to P-selectin. Recent evidence suggests that the blockade of P-selectin/PSGL-1 interactions provides a viable therapeutic option for the treatment of many inflammatory diseases. Herein, we report the total synthesis of threonine bearing sialyl LewisX (sLeX) linked to a Core-1- O-hexasaccharide 1, as a key glycan of the N-terminal domain of PSGL-1. A convergent synthesis using α-selective sialylation and a regioselective [4+2] glycosylation are the key features of this synthesis.