Preliminary investigation of the structure of the carbohydrate component of Vicia graminea lectin, a plant glycoprotein

A review of Vicieae lectins studies: End of the book or a story in the writing?

Vicieae tribe, Leguminosae family (Fabaceae), has been extensively studied. In particular, the study of lectins. The purification, physicochemical and structural characterizations of the various purified lectins and the analysis of their relevant biological activities are ongoing. In this review, several works already published about Vicieae lectins are addressed. Initially, we presented the purification protocols and the physicochemical aspects, such as specificity for carbohydrates, optimal activity in the face of variations in temperature and pH, as well metals-dependence. Following, structural characterization studies are highlighted and, finally, various biological activities already reported are summarized. Studies on lectins in almost all genera (Lathyrus, Lens, Pisum and Vicia) are considered, with the exception of Vavilovia which studies of lectins have not yet been reported. Like other leguminous lectins, Vicieae lectins present heterogeneous profiles of agglutination profiles for erythrocytes and other cells of the immune system, and glycoproteins. Most Vicieae lectins consist of two subunits, α and β, products of a single precursor protein derived from a single gene. The differences between the isoforms result from varying degrees of proteolytic processing. Along with the identification of these molecules and their characteristics, biological activities become very relevant and robust for both basic and applied research.

Mapping glycoconjugate-mediated interactions of marine Bacteroidetes with diatoms

The degradation of diatoms is mainly catalyzed by Bacteroidetes and this process is of global relevance for the carbon cycle. In this study, a combination of catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) and fluorescent lectin binding analysis (FLBA) was used to identify and map glycoconjugates involved in the specific interactions of Bacteroidetes and diatoms, as well as detritus, at the coastal marine site Helgoland Roads (German Bight, North Sea). The study probed both the presence of lectin-specific extracellular polymeric substances (EPS) of Bacteroidetes for cell attachment and that of glycoconjugates on diatoms with respect to binding sites for Bacteroidetes. Members of the clades Polaribacter and Ulvibacter were shown to form microcolonies within aggregates for which FLBA indicated the presence of galactose containing slime. Polaribacter spp. was shown to bind specifically to the setae of the abundant diatom Chaetoceros spp., and the setae were stained with fucose-specific lectins. In contrast, Ulvibacter spp. attached to diatoms of the genus Asterionella which bound, among others, the mannose-specific lectin PSA. The newly developed CARD-FISH/FLBA protocol was limited to the glycoconjugates that persisted after the initial CARD-FISH procedure. The differential attachment of bacteroidetal clades to diatoms and their discrete staining by FLBA provided evidence for the essential role that formation and recognition of glycoconjugates play in the interaction of bacteria with phytoplankton.

Synthesis of four structural elements of xylose-containing carbohydrate chains from N-glycoproteins

The synthesis of the oligosaccharides beta-D-Xylp-(1----2)-beta-D-Manp-OMe (12), beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----6)]-beta-D-Manp+ ++-OMe (17), beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----3)]-beta-D-Manp+ ++-OMe (21), and beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----3)] [alpha-D-Manp-(1----6)]-beta-D-Manp-OMe (25) is described. Methyl 3-O-benzyl-4,6-O-isopropylidene-beta-D-mannopyranoside (6) was prepared from the corresponding glucoepimer (4) by oxidation, followed by stereoselective reduction. Condensation of 6 with 2,3,4-tri-O-acetyl-alpha-D-xylopyranosyl bromide in the presence of mercuric cyanide gave a 1:9 mixture of methyl 3-O-benzyl-4,6-O-isopropylidene-2-O-(2,3,4- tri-O-acetyl-alpha- (7a) and -beta-D-xylopyranosyl)-beta-D-mannopyranoside (7), and then 7 was converted into the acetylated disaccharide-glycoside 11. Regioselective mannosylation, with 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl bromide, at position 6 of deisopropylidenated 7 (8), using mercuric bromide as a promoter, afforded the trisaccharide-glycoside derivative 13, which was transformed into the acetylated trisaccharide-glycoside 16. The disaccharide derivative 10, obtained from 8, and the trisaccharide derivative 15, obtained from 13, were glycosylated at position 3 with O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl)trichloroacetimidate (19), using trimethylsilyl triflate as a promoter, giving rise to acetylated tri- (20) and tetra-saccharide (24) derivatives, respectively. O-Deacetylation of 11, 16, 20, and 24 gave 12, 17, 21, and 25, respectively.

1H- and 13C-n.m.r. assignments for structural elements of xylose-containing N-linked oligosaccharides, using 1D-and 2D-n.m.r. experiments

1H-N.m.r. and 13C-n.m.r. spectral assignments for synthetic beta-D-Xyl-(1----2)-beta-D-Man-OMe, beta-D-Xyl-(1----2)-[alpha-D-Man-(1----3)]-beta-D-Man-OMe, beta-D-Xyl-(1----2)-[alpha-D-Man-(1----6)]-beta-D-Man-OMe, and beta-D-Xyl-(1----2)-[alpha-D-Man-(1----3)]-[alpha-D-Man-(1----6)]- beta-D-Man-OMe, which are structural elements of xylose-containing carbohydrate chains from N-glycoproteins, have been made on the basis of 1D and 2D (DQF 1H-1H COSY, HOHAHA) 500-MHz 1H-n.m.r. spectroscopy and 1D 50-MHz 13C-n.m.r. spectroscopy, respectively.

Purification of GP57, and auxin-regulated extracellular glycoprotein of carrots, and its immunocytochemical localization in dermal tissues

A glycoprotein (GP57) was purified by ion-exchange and hydroxylapatite column chromatography from the 70%-ethanol precipitate of culture medium of non-embryogenic carrot cells (Daucus carota L.) grown with 2,4-dichlorophen-oxyacetic acid (2,4-D). Its apparent molecular mass (M r) was estimated to be 57000 by sodium dodecylsulfate-polyacrylamide gel electrophoresis and 50000 by gel filtration. GP57 contained 14% (w/w) carbohydrate; the M r of the peptide portion was estimated to be 55000 after deglycosylation by trifluoromethanesulfonic acid. GP57 is composed of two polypeptides with the same Mr and with very similar amino-acid composition but different pI values, 8.8 and 9.5. Both are rich in aspartic acid, serine and threonine, and may possess N-linked oligosaccharide chains, including fucose and xylose. A monoclonal antibody (MAb) against the purified GP57 reacted with both the pI 8.8 and the 9.5 components, as well as the deglycosylated GP57. Immunoblotting with the MAb indicated that GP57 is synthesized in and released from cultured cells which have been supplied with auxin. In immunocytochemical studies, GP57 was found in the space between the embryo and the endosperm of dry seeds, and its content decreased during germination. GP57 was also found in the endodermis and epidermis of young roots, the periderm of mature taproots, and the epidermis of petioles and young leaves.

Primary structure of an N-glycosidic carbohydrate unit derived from Sophora japonica lectin

The lectin isolated from Sophora japonica seeds is a glycoprotein which binds oligosaccharides with non-reducing terminal Gal beta(1----3/4)GlcNac beta 1----units. The carbohydrate moiety of the lectin is composed of fucose, xylose, mannose and N-acetylglucosamine. The major glycopeptide of the lectin, prepared by pronase digestion, was derivatized with fluorescein isothiocyanate, purified by PAGE and examined by exoglycosidase digestion as well as purified by gel filtration through Bio-Gel P6-DG and investigated by methylation analysis and 400-MHz 1H-NMR spectroscopy. The primary structure of the glycopeptide was established to be as follows. (Formula: see text). Structures similar to this containing a (beta 1-2)xylosyl substituent on the core beta-mannosyl residue and an inner core (alpha 1-3)fucosyl substituent seem to occur frequently in plant glycoproteins.

Characterization of the carbohydrate moiety of Clerodendron trichotomum lectins. Its structure and reactivity toward plant lectins

Lectins were isolated from fruits and leaves of Clerodendron trichotomum by affinity chromatography on lactamyl-Sepharose. The purified lectins (C. trichotomum agglutinin: CTA) were homogeneous on SDS/polyacrylamide gel electrophoresis, and the carbohydrate moiety was characterized by physicochemical and immunochemical methods. The asparagine-linked oligosaccharides were released by treatment with N-oligosaccharide glycopeptidase (almond, EC 3.5.1.52) of peptic glycopeptides obtained from fruit CTA, and separated by gel filtration and thin-layer chromatography. The structure of the predominant oligosaccharide was determined as Xyl beta 1----2 (Man alpha 1----6)(Man alpha 1----3)Man beta 1----4GlcNAc beta 1----4(Fuc alpha 1----3)GlcNAc by high-performance liquid chromatography, sugar analysis and 1H-NMR spectroscopy. The reactivity of the carbohydrate moiety of CTA toward various lectins was studied. Fruit and leaf CTAs were applied to polyacrylamide gel electrophoresis, transferred to nitrocellulose sheets and detected with horseradish-peroxidase-conjugated lectins. Concanavalin A, lentil lectin, pea lectin, Vicia faba lectin and Ulex europeus agglutinin I, but not wheat germ lectin, bound to fruit CTA. The results indicate new binding properties of these plant lectins: a beta-xylosyl residue substituted at C-2 of the beta-mannosyl residue of N-linked oligosaccharide does not affect the binding with mannose-specific lectins, lentil, pea and Vicia faba lectins can bind to N-linked oligosaccharides containing an alpha-L-fucosyl residue attached to C-3 of the asparagine-linked N-acetyl-D-glucosamine residue, and Ulex europeus agglutinin I can bind to the (alpha 1----3)-linked fucose residue of the N-linked oligosaccharide.