Chemical characterization of the lectin from Amaranthus leucocarpus syn. hypocondriacus by 2-D proteome analysis

Neuroinflammation induced by amyloid β25-35 modifies mucin-type O-glycosylation in the rat's hippocampus

Amyloid-β (Aβ) plays a relevant role in the neurodegenerative process of Alzheimer's disease (AD). The 25-35 peptide of amyloid-β (Aβ25-35) induces the inflammatory response in brain experimental models. Mucin-type O-glycosylation has been associated with inflammation of brain tissues in AD, thus in this work, we aimed at identifying changes in the glycosylation profile generated by the injection of Aβ25-35 into the CA1 of the hippocampus of rats, using histochemistry with lectins. Our results indicate that 100μM Aβ25-35 induce increased recognition of the Amaranthus leucocarpus lectin (ALL) (specific for Galβ1,3-GalNAcα1,0-Ser/Thr); whereas concanavalin A (Con A) (specific for α-Man) showed no differences among treated and control groups of rats. Jacalin and peanut agglutinin (Galβ1,3GalNAcα1,0-Ser/Thr) showed no recognition of brain cells of control or treated rats. After 6-h treatment of the tissue with trypsin or with 200mM GalNAc, the interaction with ALL was inhibited. Immunohistochemistry showed positive anti-NeuN and ALL-recognition of neurons; however, anti-GFAP and anti-CD11b showed no co-localization with ALL. The ALL+ neurons revealed the presence of cytochrome C in the cytosol and active caspase 3 in the cytosol and nucleus. Administration of the interleukin-1 receptor antagonist (IL-1RA) to Aβ25-35-treated rats diminished neuroinflammation and ALL recognition. These results suggest a close relationship among over-expression of mucin-type O-glycosylation, the neuroinflammatory process, and neuronal death.

Amaranthin-Like Proteins with Aerolysin Domains in Plants

Amaranthin is a homodimeric lectin that was first discovered in the seeds of Amaranthus caudatus and serves as a model for the family of amaranthin-like lectins. Though these lectins have been purified and characterized only from plant species belonging to the Amaranthaceae, evidence accumulated in recent years suggests that sequences containing amaranthin domains are widely distributed in plants. In this study, 84 plant genomes have been screened to investigate the distribution of amaranthin domains. A total of 265 sequences with amaranthin domains were retrieved from 34 plant genomes. Within this group of amaranthin homologs, 22 different domain architectures can be distinguished. The most common domain combination consists of two amaranthin domains followed by a domain with sequence similarity to aerolysin. The latter protein belongs to the group of β-pore-forming toxins produced by bacteria such as Aeromonas sp. and exerts its toxicity by making transmembrane pores in the target membrane, as such facilitating bacterial invasion. In addition, amaranthin domains also occur in association with five other protein domains, including the fascin domain, the alpha/beta hydrolase domain, the TRAF-like domain, the B box type zinc finger domain and the Bet v1 domain. All 16 amaranthin-like proteins retrieved from the cucumber genome possess a similar domain architecture consisting of two amaranthin domains linked to one aerolysin domain. Based on phylogenetic differences, four sequences were selected for further investigation. Subcellular localization studies revealed that the amaranthin-like proteins from cucumber reside in the cytoplasm and/or the nucleus. Analyses using qPCR showed that the transcript levels for the amaranthin-like sequences are typically low and expression levels vary among tissues during the development of cucumber plants. Furthermore, the expression of amaranthin-like genes is enhanced after different abiotic stresses, suggesting that these amaranthin-like proteins play a role in the stress response. Finally, molecular modeling was performed to unravel the structure of amaranthin-like proteins and their carbohydrate-binding sites. This study provided valuable information on the distribution, phylogenetic relationships, and possible biological roles of amaranthin-like proteins in plants.

Amaranthus leucocarpus lectin recognizes a moesin-like O-glycoprotein and costimulates murine CD3-activated CD4(+) T cells

The Galβ1,3GalNAcα1,O-Ser/Thr specific lectin from Amaranthus leucocarpus (ALL) binds a ∼70 kDa glycoprotein on murine T cell surface. We show that in the absence of antigen presenting cells, murine CD4⁺ T cells activated by an anti-CD3 antibody plus ALL enhanced cell proliferation similar to those cells activated via CD3/CD28 at 48 h of culture. Moreover, ALL induced the production of IL-4, IL-10, TNF-alpha, and TGF-beta in CD3-activated cells. Proteomic assay using two-dimensional electrophoresis and far-Western blotting, ALL recognized two prominent proteins associated to the lipid raft microdomains in CD3/CD28-activated CD4⁺ T cells. By mass spectrometry, the peptide fragments from ALL-recognized proteins showed sequences with 33% homology to matricin (gi|347839 NCBInr) and 41% identity to an unnamed protein related to moesin (gi|74186081 NCBInr). Confocal microscopy analysis of CD3/CD28-activated CD4⁺ T cells confirmed that staining by ALL colocalized with anti-moesin FERM domain antibody along the plasma membrane and in the intercellular contact sites. Our findings suggest that a moesin-like O-glycoprotein is the ALL-recognized molecule in lipid rats, which induces costimulatory signals on CD4⁺ T cells.

The Amaranthus leucocarpus lectin enhances the anti-CD3 antibody-mediated activation of human peripheral blood CD4+ T cells

Activation of CD4(+) T cells plays a main role in adaptive immune response by regulating cellular and humoral immunity via processes associated with changes in cell surface oligosaccharide receptors. Lectins are glycoproteins that specifically recognize oligosaccharides and have been used to characterize changes in oligosaccharides present on T cell surface and their effects on activation. A lectin from Amaranthus leucocarpus seeds (ALL) is specific for glycoprotein structures containing galactose-N-acetylgalactosamine and is able to bind to human and murine CD4(+) T cells, however, its effect on activation remains unclear. We examined the effect of ALL on the activation of peripheral blood human CD4(+) T cells and analyzed cell proliferation, expression of the activation-associated molecule CD25, secretion of the activation-dependent cytokine interleukin (IL)-2 and intracellular calcium influx changes using flow cytometry. CD4(+) T cells were stimulated with anti-CD3 antibodies that provided the first activation signal in the presence or absence of ALL. ALL alone did not induce CD4(+) T cell activation but when also stimulated with anti-CD3 antibodies, ALL up-regulated CD25 expression, cell proliferation, IL-2 secretion and an intracellular calcium influx in a dose-dependent manner. In addition, ALL recognized CD4(+) T cells expressing the CD69 and Ki67 molecules expressed only by activated T cells and induced production of the TH1-type cytokine interferon-gamma. Our findings indicate that ALL binds to human activated CD4(+) T cells and enhances the degree of activation of CD4(+) T cells that are stimulated with anti-CD3 antibodies. ALL provides a new tool for analyzing T cell activation mechanisms.

Amaranthus leucocarpus lectin (ALL) enhances anti-CD3-dependent activation of murine T cells and promotes cell survival

The Galβ1,3GalNAc-specific lectin from Amaranthus leucocarpus (ALL) shows a differential binding pattern on murine thymocytes, peripheral and activated CD4(+) and CD8(+) T cells. Although ALL detects activation-related changes in T cell surface carbohydrate moieties, no study has been performed to examine the effect of ALL on T cell activation. In this study, we analyzed the anti-CD3-dependent activation of murine T cells in the presence of ALL by measuring proliferation, surface activation marker expression, and IL-2 secretion using total cells from the lymph node. The results showed that ALL did not significantly induce T cell activation but did enhance anti-CD3-dependent activation of both CD4(+) and CD8(+) T cells. In addition, ALL protected T cells from spontaneous apoptosis and increased cell survival in serum-free culture conditions. Our findings indicate that ALL alone does not affect T cell activation, but do suggest that ALL has an anti-CD3-dependent co-stimulatory-like effect on T cell activation. Moreover, ALL promotes cell survival in regular and serum-free culture conditions. This study is the first report of a non-mitogenic T cell-binding lectin that can induce a possible costimulatory-like effect and provides a new tool for understanding how glycosylation impacts the T cell response.

Mass spectrometric characterization of isoform variants of peanut (Arachis hypogaea) stem lectin (SL-I)

Matrix assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometric (MS) analysis of purified Arachis hypogaea stem lectin (SL-I) and its tryptic digests suggested it to be an isoformic glucose/mannose binding lectin. Two-dimensional gel electrophoresis of SL-I indicated six isoforms (A1-A6), which were confirmed by Western blotting and MALDI-TOF MS analysis. Comparative analysis of peptide mass spectra of the isoforms matched with A. hypogaea lectins with three different accession numbers (Q43376_ARAHY, Q43377_ARAHY, Q70DJ5_ARAHY). Tandem mass spectrometric (MS/MS) analysis of tryptic peptides revealed these to be isoformic variants with altered amino acid sequences. Among the peptides, the peptide T12 showed major variation. The (199)Val-Ser-Tyr-Asn(202) sequence in peptide T12 of A1 and A2 was replaced by (199)Leu-Ser-His-Glu(202) in A3 and A4 (T12') while in A5 and A6 this sequence was (199)Val-Ser-Tyr-Val(202) (T12''). Peptide T1 showed the presence of (10)Asn in the isoforms A1-A5 while in A6 this amino acid was replaced by (10)Lys (T1'). Overall amino acid sequence as identified by MS/MS showed a high degree of similarity between A1, A2 and among A3, A4, A5. Carbohydrate binding domain and adenine binding site seem to be conserved.

A lectin from Sesbania aculeata (Dhaincha) roots and its possible function

A lectin was isolated from the roots of Sesbania aculeata. This is a glucose specific lectin having 39 kDa subunit molecular weight. The expression of this lectin was found to be developmentally regulated and observed to be the highest in the second week. The lectin was purified by affinity chromatography using Sephadex G-50 and found to have 28% homology with Arabidopsis thaliana lectin-like protein (accession No. CAA62665). The lectin binds with lipopolysaccharide isolated from different rhizobial strains indicating the plants interaction with multiple rhizobial species.

Purification and mass spectrometric characterization of Sesbania aculeata (Dhaincha) stem lectin

A glucose specific lectin (STA) was isolated from Sesbania aculeata stem by using Sephadex G-50 affinity column chromatography. The lectin is a glycoprotein having 29 kDa subunit molecular weight. Two dimensional gel electrophoresis analysis revealed that the lectin existed in two isomeric forms with varied carbohydrate content as analyzed by high performance anion exchange chromatography-pulsed amperometric detector (HPAEC-PAD). Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) and N-terminal sequence (LDSLSFTYNNFE) analysis of this lectin showed 95% homology with stem lectin SL-I (accession no. AJ585523) from peanut plant. The nucleotide sequence of the lectin (STA) was submitted to the gene bank (accession no. EU263636).

Characterization of lectin aggregates in the hemolymph of freshwater prawn Macrobrachium rosenbergii

In invertebrates, lectins play relevant roles in innate immunity; however, their regulatory mechanisms have not been identified yet. In this work, we purified, by gel filtration and affinity chromatography, lectin aggregates circulating in the hemolymph of the freshwater prawn Macrobrachium rosenbergii and compared their physicochemical properties with a previously described lectin (MrL). High-molecular weight MrL aggregates (MrL-I) lack hemagglutinating activity and showed bands of 62.1, 67.1 and 81.4 kDa, whereas MrL-III, which corresponds to MrL, showed hemagglutinating activity and is constituted by a single 9.6-kDa band as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. MrL-I and MrL-III showed similar amino acid composition but different carbohydrates concentration. Edman degradation indicated NH2-terminal sequence of five amino acids for the 9.6-kDa MrL-III (DVPLL/A) and eleven for the main 81.4-kDa band identified in MrL-I (DVPLL/AXKQQQD); analysis by MALDI-TOF indicated a different tryptic pattern for MrL-I and MrL-III. MrL-I was recognized by monoclonal antibodies against MrL-III. Circular dichroism indicated that the secondary structure in both proteins is similar and contains 23% of beta-sheet and 24% of alpha-helix. Our results suggest that differential posttranslational processes that favor aggregation are involved in regulating the activity of the lectin.

Analysis of the lectins from teosinte (Zea diploperennis) and maize (Zea mays) coleoptiles

To identify molecular evidence of the common origin of maize and teosinte, a lectin from teosinte coleoptile (TCL) was purified, through affinity chromatography on a lactosyl-Sepharose column, and some of the physicochemical parameters were compared with those from the maize coleoptile lectin (CCL). TCL is a 92 kDa glycoprotein constituted mainly by aspartic, glutamic, glycine, leucine, and lysine residues; in minor proportion, methionine and cysteine were also found. The glycannic portion of the lectin, which corresponds to 10% w/w, is composed by Gal, Man, and GlcNAc. CCL is an 88.7 kDa glycoprotein that contains 12% sugars by weight; its sugar and amino acid compositions are similar to those of TCL. TCL is formed by two isoforms identified through acidic electrophoresis, whereas CCL is constituted by a single molecular form. The NH(2) termini of both TCL isoforms are blocked, but their amino acid sequences determined from tryptic peptides by matrix-assisted laser desorption ionization time-of-flight) indicated that TCL isoforms have no homology with other mono- or dicotyledonous lectins, including CCL. TCL, just as CCL, showed hemagglutinating activity toward animal erythrocytes, including human A, B, and O. Hapten inhibition assays indicated that although TCL shows broader sugar specificity than CCL, it recognizes Gal in O- and N-glycosidically linked glycans. Both lectins are equally well recognized by antibodies against TCL.