Role of Phytomolecules in the Treatment of Obesity: Targets, Mechanisms and Limitations.

Obesity has become a worldwide health problem. It triggers additional co-morbidities like cardiovascular diseases, cancer, depression, sleep disorders, gastrointestinal problems and many more. Excess accumulation of fat in obesity could be caused by many factors like sedentary lifestyle, consumption of high-fat diet, genetic predisposition, etc. Imbalanced energy metabolism i.e., greater energy consumption than utilisation, invariably underlies obesity. Considering the high prevalence and continuous, uncontrolled increase of this major public health issue, there is an urgent need to find appropriate therapeutic agents with minimal or no side effects. The high prevalence of obesity in recent years has led to a surge in the number of drugs available in the market that claim to control obesity. Although there is a long list of medicines and management strategies that are available, selecting the right therapeutic intervention and feasible management of obesity is a challenge. Several phytochemicals like hydroxycitric acid, flavonoids, tannins, anthocyanins, phytohaemagglutinin, thymoquinone and epigallocatechin gallate have been shown to possess promising anti-obesity properties. However, studies providing information on how various phytochemicals exert their anti-obesity effects are inadequate. This calls for more experimentation in this less explored area of research. Additionally, the complication of obesity arises when it is a result of multiple factors and associated with a number of co-morbidities. In order to handle such complexities, combinatorial therapeutic interventions become effective. In this review, we have described the medicinal chemistry of different highly effective phytochemicals which can be used in the effective treatment and management of obesity.

Calcium redistribution contributes to the hard-to-cook phenotype and increases PHA-L lectin thermal stability in common bean low phytic acid 1 mutant seeds.

Seed phytic acid reduces mineral bioavailability by chelating minerals. Consumption of common bean seeds with the low phytic acid 1 (lpa1) mutation improved iron status in human trials but caused adverse gastrointestinal effects, presumably due to increased stability of lectin phytohemagglutinin L (PHA-L) compared to the wild type (wt). A hard-to-cook (HTC) defect observed in lpa1 seeds intensified this problem. We quantified the HTC phenotype of lpa1 common beans with three genetic backgrounds. The HTC phenotype in the lpa1 black bean line correlated with the redistribution of calcium particularly in the cell walls, providing support for the "phytase-phytate-pectin" theory of the HTC mechanism. Furthermore, the excess of free cations in the lpa1 mutation in combination with different PHA alleles affected the stability of PHA-L lectin.

Regulation of neutrophil function by selective targeting of glycan epitopes expressed on the integrin CD11b/CD18.

Polymorphonuclear neutrophils (PMNs) play a critical role in the innate immune response to invading pathogens. However, dysregulated mucosal trafficking of PMNs and associated epithelial tissue damage is a pathological hallmark of numerous inflammatory conditions including inflammatory bowel disease. The glycoprotein CD11b/CD18 plays a well-described role in regulating PMN transepithelial migration and PMN inflammatory functions. Previous studies have demonstrated that targeting of the N-linked glycan Lewis X on CD11b blocks PMN transepithelial migration (TEpM). Given evidence of glycosylation-dependent regulation of CD11b/CD18 function, we performed MALDI TOF Mass Spectrometry (MS) analyses on CD11b/CD18 purified from human PMNs. Unusual glycan epitopes identified on CD11b/CD18 included high Mannose oligosaccharides recognized by the Galanthus Nivalis lectin and biantennary galactosylated N-glycans recognized by the Phaseolus Vulgaris erythroagglutinin lectin. Importantly, we show that selective targeting of glycans on CD11b with such lectins results in altered intracellular signaling events that inhibit TEpM and differentially affect key PMN inflammatory functions including phagocytosis, superoxide release and apoptosis. Taken together, these data demonstrate that discrete glycan motifs expressed on CD11b/CD18 such as biantennary galactose could represent novel targets for selective manipulation of CD11b function and reduction of PMN-associated tissue damage in chronic inflammatory diseases.

Establishment of immunity against Epstein-Barr virus infection in a patient with CHARGE/complete DiGeorge syndrome after peripheral blood lymphocyte transfusion.

CHARGE syndrome is a rare congenital malformation syndrome which may share symptoms with DiGeorge syndrome. Complete DiGeorge syndrome (cDGS) is a severe form of DiGeorge syndrome, characterized by a CD3+ T-cell count of <50/mm3 due to athymia, and is fatal without immunologic intervention. We performed peripheral blood lymphocyte transfusion (PBLT) from an HLA-identical sibling without pretransplant conditioning in a CHARGE/cDGS patient with a novel CHD7 splice site mutation. Cyclosporine and short-term methotrexate were used for graft versus host disease (GVHD) prophylaxis, and neither acute nor chronic GVHD was observed. After PBLT, T-cell proliferative response to phytohemagglutinin and concanavalin A recovered, and intractable diarrhea improved. EBV infection, evidenced by a gradual increase in the viral genome copy number to a maximum of 2861 copies/µgDNA on day 42 after PBLT, resolved spontaneously. HLA A2402 restricted, EBV-specific CTLs were detected from peripheral blood on day 148, and EBV seroconversion was observed on day 181. Thus, EBV-specific immunity was successfully established by PBLT. Our results indicate that PBLT is a simple and effective therapy to reconstitute immune systems in CHARGE/DiGeorge syndrome.

Cytokines Produced by Lymphocytes in the Incompetent Great Saphenous Vein.

The pathogenesis of chronic venous disease (CVD) remains unclear, but lately inflammation is suggested to have an important role in its development. This study is aimed at assessing cytokines released by lymphocytes in patients with great saphenous vein (GSV) incompetence. In 34 patients exhibiting oscillatory flow (reflux) in GSV, blood was derived from the cubital vein and from the incompetent sapheno-femoral junction. In 12 healthy controls, blood was derived from the cubital vein. Lymphocyte culture with and without stimulation by phytohemagglutinin (PHA) was performed. Interleukins (IL) 1ß, 2, 4, 10, 12 (p70), and 17A; interleukin 1 receptor α (IL-1ra); tumor necrosis factor-α (TNF-α); interferon-gamma (IFN-γ); and RANTES were assessed in culture supernatants by the Bio-Plex assay. In both stimulated and unstimulated samples, in the examined group, IL-1ß and IFN-γ had higher concentrations and RANTES had lower concentrations when compared to those in the control group. In the examined group, IL-4 and IL-17A had higher concentrations without stimulation and TNF-α had higher concentrations with stimulation. The GSV samples had higher IL-2, IL-4, IL-12 (p70), and IFN-γ concentrations without stimulation and lower IL-2 and TNF-α concentrations with stimulation when compared to those of the upper limb in the examined group. These observations indicate that the oscillatory flow present in incompetent veins causes changes in the cytokine production by lymphocytes, promoting a proinflammatory profile. However, the relations between immunological cells, cytokines, and the endothelium require more insight.

The molecular mechanisms involved in lectin-induced human platelet aggregation.

We have compared the effect of three legume lectins, wheat germ agglutinin (WGA), Phaseolus vulgaris agglutinin (PHA) and Lens culinaris agglutinin (LCA), on the function of human platelets. We have found that WGA is more active than PHA in stimulating platelet activation/aggregation, while LCA has no effect. Studies on the mechanisms involved show that WGA and PHA induce phosphorylation/activation of PLCγ2 and increase [Ca2+]i. For the first time, it has been shown that Src/Syk pathway, the adapter protein SLP-76 and the exchange protein VAV, participate in the PLCγ2 activation by these lectins. Moreover WGA and PHA stimulate the PI3K/AKT pathway. PI3K, through its product phosphatidylinositol-3,4,5-trisphosphate activates Bruton's tyrosine kinase (BTK) and contributes to PLCγ2 activation. In conclusion, our findings suggest that PLCγ2 activation induced by WGA and PHA is regulated by Src/Syk and by PI3K/BTK pathways through their concerted action.

Comprehensive analysis of α 2-3-linked sialic acid specific Maackia amurensis leukagglutinin reveals differentially occupied N-glycans and C-terminal processing.

Seeds of Maackia amurensis constitutes two sialic acid specific agglutinins known as leukagglutinin and hemagglutinin. Maackia amurensis leukagglutinin (MAL) recognizes α2-3-linked sialic acid present mainly in N-glycans and composed of two disulfide linked monomers. It exhibits potential N-glycosylation sites (four PNGs) which have been assumed to undergo differential occupancy. In this study we have characterized the site specific macro- and microheterogeneity of monomers in detail by analysing N-glycopeptides and peptides through liquid chromatography coupled to ion trap mass spectrometer in MS3 mode (LC-MSn). We observed the presence of mainly paucimannose N-glycans at Asn61, Asn113 and Asn191 whereas a high mannose type with varying Man5-9 occurs at Asn179. Interestingly Asn179 and Asn191 exhibited differential occupancy which was evident by the presence of non-glycosylated peptides. This has contributed to the difference in molecular mass of monomers upon SDS-PAGE. Further the presence of disulfide linked peptides confirmed the covalent linkage of monomers which also undergoes uniform C-terminal processing.

Gamma delta T cells are early responders to Mycobacterium avium ssp. paratuberculosis in colostrum-replete Holstein calves.

Peripheral blood mononuclear cells (PBMC) and mesenteric node lymphocytes (MNL) were obtained from 30 calves that were assigned randomly at birth to 1 of 6 treatment groups with 5 calves per treatment in a 14-d study: (1) colostrum-deprived (CD), no vitamins; (2) colostrum-replacer (CR), no vitamins; (3) CR, vitamin A; (4) CR, vitamin D3; (5) CR, vitamin E; (6) CR, vitamins A, D3, E. Calves were injected with appropriate vitamin supplements and fed pasteurized whole milk (CD calves) or fractionated colostrum replacer (CR calves) at birth. Thereafter, all calves were fed pasteurized whole milk fortified with vitamins according to treatment group. Calves were orally inoculated with 108 cfu of Mycobacterium avium ssp. paratuberculosis (MAP) on d 1 and 3. The PBMC and MNL harvested on d 13 were analyzed by flow cytometry as fresh cells, after 3-d culture with phytohemagglutinin (PHA), and after 6-d culture with a whole-cell sonicate of MAP (MPS). Peripheral γδ T cells were a predominant lymphocyte subset in neonatal calves, with a decreased percentage noted in CD calves compared with CR calves. As well, CD25 expression was higher in γδ T cells compared with other cell subsets, regardless of treatment group. Stimulation of PBMC with PHA resulted in increased CD4+ and CD8+ subsets, whereas MNL response was dominated by expansion of B-cell subpopulations. Stimulation with PHA and MPS decreased the relative abundance of PBMC γδ T cells, but MNL γδ T cells increased upon stimulation with MPS. These results identify γδ T cells as key early responders to intracellular infection in neonatal calves and suggest that colostrum may be an important mediator of this response.

Possible mechanisms of Leukoagglutinin induced apoptosis in human cells in vitro.

Leukoagglutinin is one of the phytohemagglutinin isolectins isolated from Phaseolus vulgaris. In our recent study, we showed that this lectin is able to influence the growth of human cancer cells in vitro. In addition, using the acridine orange and ethidium bromide staining, we found that leukoagglutinin can induce apoptosis. In order to understand the molecular mechanisms of induction of apoptosis, we performed computational modeling with subsequent experimental verification of theoretical data in vitro. We developed computational models of leukoagglutinin interaction with pro- (FasR and TNFR) and anti-apoptotic (IGF-1 and EGFR) receptors, and confirmed that leukoagglutinin may specifically interact with these receptors. Furthermore, we proved that leukoagglutinin can induce apoptosis in cancer (HEp-2) and non-cancer (4BL) cells, and observed that PHA-L is able to induce apoptosis through the up-regulation of Bax protein and activation of the effector caspase-3 and initiator caspase-8. However, these proteins have no effect on the Bcl-2 expression level.

ß-MSCs: successful fusion of MSCs with ß-cells results in a ß-cell like phenotype.

Bone marrow mesenchymal stromal cells (MSC) have anti-inflammatory, anti-apoptotic and immunosuppressive properties and are a potent source for cell therapy. Cell fusion has been proposed for rapid generation of functional new reprogrammed cells. In this study, we aimed to establish a fusion protocol of bone marrow-derived human MSCs with the rat beta-cell line (INS-1E) as well as human isolated pancreatic islets in order to generate insulin producing beta-MSCs as a cell-based treatment for diabetes.Human eGFP+ puromycin+ MSCs were co-cultured with either stably mCherry-expressing rat INS-1E cells or human dispersed islet cells and treated with phytohemagglutinin (PHA-P) and polyethylene glycol (PEG) to induce fusion. MSCs and fused cells were selected by puromycin treatment.With an improved fusion protocol, 29.8 ± 2.9% of all MSCs were ß-MSC heterokaryons based on double positivity for mCherry and eGFP.After fusion and puromycin selection, human NKX6.1 and insulin as well as rat Neurod1, Nkx2.2, MafA, Pdx1 and Ins1 mRNA were highly elevated in fused human MSC/INS-1E cells, compared to the mixed control population. Such induction of beta-cell markers was confirmed in fused human MSC/human dispersed islet cells, which showed elevated NEUROD1, NKX2.2, MAFA, PDX1 and insulin mRNA compared to the mixed control. Fused cells had higher insulin content and improved insulin secretion compared to the mixed control and insulin positive beta-MSCs also expressed nuclear PDX1. We established a protocol for fusion of human MSCs and beta cells, which resulted in a beta cell like phenotype. This could be a novel tool for cell-based therapies of diabetes.

Quantitative approach to lectin-based glycoprofiling of thymic tissues in the control- and the dexamethasone-treated mice.

Dexamethasone (DEX) is the most commonly used synthetic glucocorticoid in treatment of various inflammatory conditions. Here we focused on evaluating the effect of DEX on apoptosis and glycan profile in the mouse thymic tissues. Histological examinations revealed that the DEX treatment cause severe alterations in thymus, such as disruption of thymic capsule, impaired epithelial cell-thymocyte contacts, cellular loss and increased apoptosis. The identification of thymic glycans in the control- and the DEX-treated mice was carried out by using a panel of five plant lectins, Maackia amurensis agglutinin (MAA), peanut agglutinin (PNA), Sambucus nigra agglutinin (SNA), Concanavalin A (ConA) and wheat germ agglutinin (WGA). Lectin histochemistry results showed that glycosylation pattern of thymus changes upon DEX treatment. For further detailed quantitative analyses of the binding intensities for each lectin, histochemical data were scored as high positive (HP), mild positive (MP) and low positive (LP) and differences among signaling densities were investigated. The staining patterns of thymic regions observed with lectin histochemistry suggest that DEX can affect the thymic glycan profile as well as thymocyte apoptosis. These results are consistent with the opinion that not only sialic acid, but also other sugar motifs may be responsible for thymocyte development.

Atomic visualization of a flipped-back conformation of bisected glycans bound to specific lectins.

Glycans normally exist as a dynamic equilibrium of several conformations. A fundamental question concerns how such molecules bind lectins despite disadvantageous entropic loss upon binding. Bisected glycan, a glycan possessing bisecting N-acetylglucosamine (GlcNAc), is potentially a good model for investigating conformational dynamics and glycan-lectin interactions, owing to the unique ability of this sugar residue to alter conformer populations and thus modulate the biological activities. Here we analyzed bisected glycan in complex with two unrelated lectins, Calsepa and PHA-E. The crystal structures of the two complexes show a conspicuous flipped back glycan structure (designated 'back-fold' conformation), and solution NMR analysis also provides evidence of 'back-fold' glycan structure. Indeed, statistical conformational analysis of available bisected and non-bisected glycan structures suggests that bisecting GlcNAc restricts the conformations of branched structures. Restriction of glycan flexibility by certain sugar residues may be more common than previously thought and impinges on the mechanism of glycoform-dependent biological functions.

Estudio de la capacidad antioxidante in vitro de Phaseolus vulgaris L. (frijol) mediante extracción asistida por microondas / Study of in vitro antioxidant capacity of Phaseolus vulgaris L. (frijol) by microwave assisted extraction

Introducción: Phaseolus vulgaris L. (frijol) es una fuente nutricional importante en Colombia, que aporta un gran contenido de sustancias bioactivas con potencial benéfico para la salud, tales como polifenoles, entre otras, que contribuyen de manera sinérgica con sus propiedades terapéuticas, y que pueden tener un efecto positivo contra algunas patologías. Objetivos: evaluar el método de extracción asistido por microondas como método alternativo para estudiar la capacidad antioxidante in vitro en ocho variedades de P. vulgaris L. cultivadas en Colombia. Métodos: semillas sin piel de P. vulgaris, deshidratadas y maceradas se sometieron a extracción asistida por microondas y extracción sólido-líquido; el contenido de fenoles se evaluó por el método de Folin-Ciocalteu y el potencial antioxidante in vitro se evaluó con base en los métodos del radical estable catión radical difenil-picrilhidrazilo y el radical catión 2,2´-azino-bis(ácido 3-etilbenzotiazolin-6-sulfunico). Resultados: el método de extracción asistido por microondas realizada en horno microondas convencional fue más eficiente respecto a la convencional ya que disminuyó la cantidad de solvente, de muestra empleada y los tiempos de extracción. Los extractos obtenidos por extracción asistida por microondas en horno microndas convencional presentaron un contenido de fenoles entre 29,36 y 60,61 g EAG/L, mientras que el método extracción sólido-líquido, estuvo entre 32,75 y 113,27 g EAG/L. El efecto anti-radicalario fue similar entre los extractos evaluados. Conclusiones: todos los extractos presentaron buena capacidad protectora contra radicales libres, y la técnica de extracción asistida por microondas en horno microndas convencional puede ser usada como método alterno para una valoración rápida, eficiente y eficaz del contenido de sustancias bioactivas en diferentes matrices, se presentó mínimas diferencias entre los resultados obtenidos, comparados con las metodologías de extracción asistida por microondas establecidas antes(AU)

Introduction: Phaseolus vulgaris L. is a representative crop of nutrient and economic importance in Colombia. Additionally, P. vulgaris is considered as a natural source of bioactives compounds, such as polyphenols, which have been associated with valuable effects on health. Objetives: to evaluate the microwave extraction assisted technique as an alternative methodology to study the antioxidant capacity of eight varieties of P. vulgaris cultivated in Colombia. Methods: dehydrated and powered seeds of P. vulgaris was subjected to microwave assisted extraction and solid-liquid extraction and. Total phenolis content was determined by Folin-Cicoulteau method and the potential antioxidant was evaluated using diphenyl-picrylhydrazyl radical stable and 2,2-Azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation assays. Results: microwave assisted extraction-Household microwave oven technique was more efficient and versatile than SLE method. The extracts obtained microwave assisted extraction-Household microwave oven methodology showed polyphenol content ranged between entre 29,36 and 60,61 g EGA/L, but SLE was over 32,75 and 113,27 g EAG/L. Conclusions: all extracts showed a considerable antioxidant potential against free radical, and microwave assisted extraction-Household microwave oven method could be used as an alternative method for fast, efficient and effective evaluation of the content of polyphenol in various matrices, with minimal differences comparing to established microwave assisted extraction techniques(AU)

White kidney bean lectin exerts anti-proliferative and apoptotic effects on cancer cells.

A 60-kDa glucosamine binding lectin, white kidney bean lectin (WKBL), was purified from Phaseolus vulgaris cv. white kidney beans, by application of anion exchange chromatography on Q-Sepharose, affinity chromatography on Affi-gel blue gel, and FPLC-size exclusion on Superdex 75. The anti-proliferative activity of WKBL on HONE1 cells and HepG2 cells was stronger than the activity on MCF7 cells and WRL68 cells (IC50 values for a 48-h treatment with WKBL on HONE1 cells: 18.8 µM; HepG2 cells: 19.7 µM; MCF7 cells: 26.9 µM; and WRL68 cells: >80 µM). The activity could be reduced by addition of glucosamine, which occupies the binding sites of WKBL, indicating that carbohydrate binding is crucial for the activity. Annexin V-FITC and PI staining, JC-1 staining and Hoechst 33342 staining revealed that apoptosis was induced on WKBL-treated HONE1 cells and HepG2 cells, but not as obviously on MCF7 cells. Cell cycle analysis also showed a slight cell cycle arrest on HONE1 cells after WKBL treatment. Western blotting suggested that WKBL induced apoptosis of HONE1 cells occurred through the extrinsic apoptosis pathway, with detection of increased level of active caspase 3, 8 and 9.

Identification and Characterization of Phytohemagglutinins from White Kidney Beans (Phaseolus vulgaris L., var. Beldia) in the Rat Small Intestine.

Although kidney bean (Phaseolus vulgaris L.) lectin toxicity is widely known, its effects in the gastrointestinal tract require further study. This investigation aimed to identify and characterize phytohemagglutinins (PHAs) in the small intestine and sera of rats following oral challenge with ground white beans. Twenty young, adult male rats were divided randomly into two groups of 10 animals each. The control group underwent gavage with a suspension of 300 mg of rodent pellet flour. The experimental group was administered a 300 mg Beldia bean flour suspension (BBFS). After 10 days of daily treatment, jejunal rinse liquid (JRL) and ileum rinse liquid and secretions, as well as sera, were collected. All biological fluids were screened for lectin reactivity using competitive inhibition ELISA, Ouchterlony double immunodiffusion, and immunoelectrophoresis techniques. The results revealed the presence of immunogenic intraluminal PHAs 3-4 h after the oral intake of the BBFS in the JRLs as well as in the jejunal and ileal secretions; however, no PHA was detectable in the rat sera. Ingestion of raw Beldia beans may lead to interaction between PHAs and the mucosa of the small intestine, potentially resulting in an inflammatory response.

Structure and Activity Changes of Phytohemagglutinin from Red Kidney Bean (Phaseolus vulgaris) Affected by Ultrahigh-Pressure Treatments.

Phytohemagglutin (PHA), purified from red kidney beans (Phaseolus vulgaris) by Affi-Gel blue affinity chromatography, was subjected to ultrahigh-pressure (UHP) treatment (150, 250, 350, and 450 MPa). The purified PHA lost its hemagglutination activity after 450 MPa treatment and showed less pressure tolerance than crude PHA. However, the saccharide specificity and α-glucosidase inhibition activity of the purified PHA did not change much after UHP treatment. Electrophoresis staining by periodic acid-Schiff (PAS) manifested that the glycone structure of purified PHA remained stable even after 450 MPa pressure treatment. However, electrophoresis staining by Coomassie Blue as well as circular dichroism (CD) and differential scanning calorimetry (DSC) assay proved that the protein unit structure of purified PHA unfolded when treated at 0-250 MPa but reaggregates at 250-450 MPa. Therefore, the hemagglutination activity tends to be affected by the protein unit structure, while the stability of the glycone structure contributed to the remaining α-glucosidase inhibition activity.

Tulane virus recognizes sialic acids as cellular receptors.

The recent discovery that human noroviruses (huNoVs) recognize sialic acids (SAs) in addition to histo-blood group antigens (HBGAs) pointed to a new direction in studying virus-host interactions during calicivirus infection. HuNoVs remain difficult to study due to the lack of an effective cell culture model. In this study, we demonstrated that Tulane virus (TV), a cultivable primate calicivirus, also recognizes SAs in addition to the previously known TV-HBGA interactions. Evidence supporting this discovery includes that TV virions bound synthetic sialoglycoconjugates (SGCs) and that treatment of TV permissive LLC-MK2 cells with either neuraminidases or SA-binding lectins inhibited TV infectivity. In addition, we found that Maackia amurensis leukoagglutinin (MAL), a lectin that recognizes the α-2,3 linked SAs, bound LLC-MK2 cells, as well as TV, by which MAL promoted TV infectivity in cell culture. Our findings further highlight TV as a valuable surrogate for huNoVs, particularly in studying virus-host interactions that may involve two host carbohydrate receptors or co-receptors for infection.

Effects of selective cleavage of high-mannose-type glycans of Maackia amurensis leukoagglutinin on sialic acid-binding activity.

BACKGROUND: Maackia amurensis leukoagglutinin (MAL) is a glycoprotein and sialic acid-binding lectin that is used widely in the detection and characterization of sialoglycoconjugates and human cancer cells. However, its N-linked glycan structure and role have yet to be determined. METHODS: The N-linked glycans were analyzed using high-performance liquid chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and the secondary structure was investigated using circular dichroism analysis. A hemagglutination assay was performed. Furthermore, surface plasmon resonance analysis, and fluorescence microscopy and fluorescence-activated cell-sorting analysis were conducted to assess the sialoglycoprotein-binding ability and its usefulness in the detection of human breast cancer MCF-7 cells, respectively. RESULTS: Analysis of the N-linked glycan structure of MAL confirmed the presence of eight glycans, comprising two α1,3-fucosylated paucimannosidic-type and six high-mannose-type glycans. Glycan analysis of MAL that had been treated with peptide N-glycosidase F (de-M-MAL) revealed that while the two α1,3-fucosylated paucimannosidic glycans remained attached following the treatment, the six high-mannose-type glycans had been completely cleaved from the original MAL. There were almost no secondary structural changes between MAL and de-M-MAL; however, the lectin activities exhibited by MAL, such as hemagglutination and binding to a sialoglycoprotein, were completely absent in de-M-MAL, and the ability to detect human breast cancer MCF-7 cells was 77% lower in de-M-MAL than in MAL. CONCLUSION: The high-mannose-type glycans in intact MAL are closely associated with its lectin activities. GENERAL SIGNIFICANCE: This is the first report of the N-linked glycan structure of MAL and the effect of high-mannose-type glycans on lectin activities.

Studying N-linked glycosylation of receptor tyrosine kinases.

Metabolic alterations have been identified as a frequent event in cancer. This is often associated with increased flux through glycolysis, and also a secondary pathway to glycolysis, hexosamine biosynthetic pathway (HBP). HBP provides substrate for N-linked glycosylation, which occurs in the endoplasmic reticulum and the Golgi apparatus. N-linked glycosylation supports protein folding and correct sorting of proteins to plasma membrane and secretion. This process generates complex glycoforms, which can be recognized by other proteins and glycosylation of receptor tyrosine kinases (RTK) can also regulate their plasma-membrane retention time. Of special interest for experimental biologists, plants produce proteins, termed lectins, which bind with high specificity to glyco-conjugates. For the purposes of molecular biology, plant lectins can be conjugated to different moieties, such as agarose beads, which enable precipitation of specifically glycosylated proteins. In this chapter, we describe in detail how to perform pull-down experiments with commercially available lectins to identify changes in the glycosylation of RTKs.

Cross-platform comparison of glycan microarray formats.

Carbohydrates participate in almost every aspect of biology from protein sorting to modulating cell differentiation and cell-cell interactions. To date, the majority of data gathered on glycan expression has been obtained via analysis with either anti-glycan antibodies or lectins. A detailed understanding of the specificities of these reagents is critical to the analysis of carbohydrates in biological systems. Glycan microarrays are increasingly used to determine the binding specificity of glycan-binding proteins (GBPs). In this study, six different glycan microarray platforms with different modes of glycan presentation were compared using five well-known lectins; concanavalin A, Helix pomatia agglutinin, Maackia amurensis lectin I, Sambucus nigra agglutinin and wheat germ agglutinin. A new method (universal threshold) was developed to facilitate systematic comparisons across distinct array platforms. The strongest binders of each lectin were identified using the universal threshold across all platforms while identification of weaker binders was influenced by platform-specific factors including presentation of determinants, array composition and self-reported thresholding methods. This work compiles a rich dataset for comparative analysis of glycan array platforms and has important implications for the implementation of microarrays in the characterization of GBPs.