Protein-polysaccharide linkages in glycoproteins from Phaseolus vulgaris

Serine and hydroxyproline participate in protein-polysaccharide linkages in hydroxyproline-poor glycoproteins from Phaseolus vulgaris cv Pinto. Most substituted hydroxyproline residues contain arabinose, galactose and glucose, but some have arabinose only. Serine residues contain arabinose, galactose and glucose.     

The formation of glycosidic bonds in yeast glycoproteins

Membranes of Saccharomyces cerevisiae were separated on urografin gradients. The specific activity of the light membranes (endoplasmic reticulum), the Golgi-like vesicles and the plasma membrane in transferring mannosyl residues from GDP-mannose to mannoproteins and to dolichyl monophosphate has been determined. The first mannose of the O-glycosidically linked manno-oligosaccharides is incorporated with the highest specific activity by the endoplasmic reticulum. The incorporation of the second to fourth mannosyl groups is catalysed with increasing activity also by the Golgi-like vesicles and the plasma membrane.The incorporation of mannosyl groups into weak alkali-stable positions (N-glycosidically linked chains) is carried out with almost the same specific activity by all three membrane fractions, however, dolicholdependent and-independent steps could not be distinguished as yet.The results are discussed in terms of a sequential addition of sugar residues along the route of export of the mannoproteins. The dolichol-dependent steps seem to occur on the endoplasmic reticulum and thus very carly in the event.Abbreviations GDP-mannose guanosine diphosphate mannose - Dol-P dolichyl monophosphate - Dol-P-mannose dolichyl monophosphate mannose     

A fluorescence assay for enzymes that cleave glycosidic linkages to produce reducing sugars

A rapid, facile, and sensitive assay has been developed for enzymes that generate reducing sugars. The assay is a modification of a method for post-HPLC column derivatization and detection of reducing sugars and is carried out in a single test tube. The assay is useful for large numbers of samples, such as those produced during purification of enzymes. Less than 500 pmol of reducing sugar can be quantitatively measured. The assay reported here is at least 10 times more sensitive than either the commonly employed parahydroxybenzoic acid hydrazide method or the recently reported bicinchoninate method, and 50 times more sensitive than the Nelson-Somogyi method.     

A characterization of the BALB/c lambda and kappa class antibodies to alpha (1,3) glycosidic linkages

The avidity relationships of kappa and lambda antibodies with specificity for the glucosyl-alpha (1,3)-glucose disaccharide epitope were compared using a solid-phase hapten inhibition assay. The kappa class antibodies, induced by the T-cell-dependent antigen, nigerosyl-keyhole limpet hemocyanin (N-KLH), and the lambda class antibodies, induced by the T-cell-independent antigen, Dextran B1355, were only marginally distinguishable (approximately equal to 10-fold) on the basis of hapten inhibition using the free disaccharide, nigerose, as inhibitor. Analysis of the binding site sizes of antibodies induced by N-KLH through inhibition with oligosaccharides of different sizes showed that the disaccharide protein antigen did not select for antibodies with smaller binding site sizes. The cellular basis for these findings is discussed.     

Selective cleavage of glycosidic linkages: Studies with the O-specific polysaccharide from Shigella dysenteriae type 3

Treatment of the O-specific polysaccharide from Shigella dysenteriae Type 3 with hydrazine in the presence of hydrazine sulphate resulted in quantitative N-deacetylation with the formation of a modified polysaccharide containing free amino groups. Oxidation of the modified polysaccharide with periodate did not destroy the 2-amino-2-deoxygalactose residues, thus indicating that they were substituted at position 3. Acid hydrolysis of the modified polysaccharide afforded 3-O-(2-amino-2-deoxy-β-D-galactopyranosyl)-D-galactose, which was identified as the N-acetyl derivative. Deamination of the modified polysaccharide with nitrous acid cleaved the 2-amino-2-deoxy-D-galactopyranosyl linkages to give a pentasaccharide as the major product, which appeared to be the modified chemical repeating unit of the O-specific polysaccharide.     

The specific substance from Pneumococcus type 34. The configuration of the glycosidic linkages

1. The specific compound from Pneumococcus type 34 was isolated from capsular material by ion-exchange chromatography. This separated it from a substance with chemical and serological properties corresponding to those reported for C-substance. 2. The configuration of the two galactofuranosyl linkages in the repeating unit of S.34 was determined and the configurations previously assigned to the other glycosidic linkages were confirmed. 3. The dephosphorylated deacetylated repeating unit is thus O-beta-d-galactofuranosyl-(1-->3)-O-alpha-d-glucopyranosyl-(1-->2)-O-beta-d-galactofuranosyl-(1-->3)-O-alpha-d-galactopyranosyl- (1-->2)-ribitol.     

Asparagine 405 of heparin lyase II prevents the cleavage of glycosidic linkages proximate to a 3-O-sulfoglucosamine residue

Heparin and heparan sulfate contain a rare 3-O-sulfoglucosamine residue critical for anticoagulation and virus recognition, respectively. The glycosidic linkage proximate to this 3-O-sulfoglucosamine is resistant to cleavage by all heparin lyases (Heps). HepII has a broad specificity. The crystal structure of the wild type HepII identified its active site and showed a close spatial proximity between Asn405 and the 3-OH group of the bound glucosamine residue. In this study, we mutated Asn405 to the less sterically demanding Ala405 or Gly405, which broadened the substrate specificity of HepII and caused it to cleave the resistant linkage proximate to the 3-O-sulfoglucosamine residue.     

Molecular dynamics study of the conformations of glycosidic linkages in sialic acid modified ganglioside GM3 analogues

The objective of the present study is to model the analogues of monosialoganglioside (GM3) by making modifications in its sialic acid residue with different substitutions in aqueous environment and to determine their structural stability based upon computational molecular dynamics. Molecular mechanics and molecular dynamics investigation was carried out to study the conformational preferences of the analogues of GM3. Dynamic simulations were carried out on the analogues of GM3 varying in the substituents at C-1, C-4, C-5, C-8 and C-9 positions of their sialic acid or Neuraminic acid (NeuAc) residue. The analogues are soaked in a periodic box of TIP3P water as solvent and subjected to a 10 ns molecular dynamics (MD) simulation using AMBER ff03 and gaff force fields with 30 ps equilibration. The analogue of GM3 with 9-N-succNeuAc (analogue5, C9 substitution) was observed to have the lowest energy of ?6112.5 kcal/mol. Graphical analysis made on the MD trajectory reveals the direct and water mediated hydrogen bonds existing in these sialic acid analogues. The preferable conformations for glycosidic linkages of GM3 analogues found in different minimum energy regions in the conformational maps were identified. This study sheds light on the conformational preferences of GM3 analogues which may be essential for the design of GM3 analogues as inhibitors for different ganglioside specific pathogenic proteins such as bacterial toxins, influenza toxins and neuraminidases.     

Selective formation of glycosidic linkages of N-unsubstituted 4-hydroxyquinolin-2-(1H)-ones

A comparative study for selective glucosylation of N-unsubstituted 4-hydroxyquinolin-2(1H)-ones into 4-(tetra-O-acetyl-β-d-glucopyranosyloxy)quinolin-2(1H)-ones is reported. Four glycosyl donors including tetra-O-acetyl-α-d-glucopyranosyl bromide, β-d-glucose pentaacetate, glucose tetraacetate and tetra-O-acetyl-α-d-glucopyranosyl trichloroacetimidate were tested, along with different promoters and reaction conditions. The best results were obtained with tetra-O-acetyl-α-d-glucopyranosyl bromide with Cs₂CO₃ in CH₃CN. In some cases the 4-O-glucosylation of the quinolinone ring was accompanied by 2-O-glucosylation yielding the corresponding 2,4-bis(tetra-O-acetyl-β-d-glucopyranosyloxy)quinoline. Next, 4-(tetra-O-acetyl-β-d-glucopyranosyloxy)quinolin-2(1H)-ones were deacetylated into 4-(β-d-glucopyranosyloxy)quinolin-2(1H)-ones with Et₃N in MeOH. In some instances the deacetylation was accompanied by the sugar-aglycone bond cleavage. Structure elucidation, complete assignment of proton and carbon resonances as well as assignment of anomeric configuration for all the products under investigation were performed by 1D and 2D NMR spectroscopy.     

Molecular identification of a polyM-specific alginate lyase from Pseudomonas sp. strain KS-408 for degradation of glycosidic linkages between two mannuronates or mannuronate and guluronate in alginate

An alginate lyase gene of a newly isolated Pseudomonas sp. strain KS-408 was cloned by using PCR with the specific primers designed from homologous nucleotide sequences. A partial protein sequence of KS-408 alginate lyase was homology-modeled on the basis of the crystal structure of A1-III alginate lyase from Sphingomonas sp. strain A1. The proposed 3-D structure of KS-408 alginate lyase shows that Asn-198, His-199, Arg-246, and Tyr-253 residues are conserved for the catalytic active site. The recombinant KS-408-1F (with signal peptide) and KS-408-2F (without signal peptide) alginate lyases with the (His)(6) tag consist of 393 (44.5 kDa) and 372 (42.4 kDa) amino acids with isoelectric points of 8.64 and 8.46, respectively. The purified recombinant KS-408 alginate lyase was very stable when it was incubated at 40 °C for 30 min. Alginate oligosaccharides produced by the KS-408-2F alginate lyase were purified on a Bio-Gel P2 column and analyzed by thin-layer chromatography, fast-protein liquid chromatography, and electrospray ionization mass spectrometry. (1)H NMR data showed that the KS-408-2F alginate lyase cleaved the glycosidic linkages between two mannuronates (mannuronate-β(1-4)-mannuronate) or mannuronate and guluronate (mannuronate-β(1-4)-guluronate), indicating that the KS-408 alginate lyase is a polyM-specific lyase.     

Investigation of stretching vibrations of glycosidic linkages in disaccharides and polysaccharides with use of IR spectra deconvolution

The results are presented for the deconvolution of IR spectra of disaccharides and polysaccharides with alpha and beta configurations of the 1 --> 4 glycosidic linkage (maltose, cellobiose, amylose, and cellulose), as well as of their corresponding monosaccharides (alpha- and beta-D-glucose) in the 1200-920 cm(-1) frequency range. It is established that a characteristic of di- and polysaccharides with 1 --> 4 glycosidic linkage is the appearance of new absorption bands in the 1175-1140 cm(-1) spectral range, as opposed to the IR spectra of monosaccharides. This can be a spectroscopic manifestation of the glycosidic linkage formation. In the 1000-970 cm(-1) frequency range, absorption bands, which are not observed in the monomer spectrum, are separated as a result of the deconvolution of the IR spectra of cellobiose and cellulose. The number of bands in this range remains unchanged for maltose and amylose, as compared to the monomer spectra. It is shown that the application of the method of deconvolution leads to a considerable enhancement in the resolution of the absorption bands in the IR spectra of mono-, di-, and polysaccharides.     

The synthesis of cyclonucleotides with fixed glycosidic bond linkages as putative agonists for P2-purinergic receptors

Cyclonucleotides with fixed glycosidic bond linkages were investigated as possible ligands for purinoceptors in PC12 cells. P2Y2-purinoceptors were not activated by the ATP analogue, 8,2'-thioanhydroadenosine-5'-triphosphate (4) and only weakly by the UTP analogue, 2,2' -anhydrouridine-5'-triphosphate (6). However, both analogues were agonists for P2X2-purinoceptors although the potencies were approximately 30-fold less than that of the parent nucleotides.     

A fluorometric assay for the quantitation of aminosugars.

A method is presented for the quantitative determination of aminosugars in glycoproteins. Glycoproteins are acid hydrolyzed and reacted with the fluorogenic reagent 1-dimethylaminonaphthalene-5-sulfonyl chloride. Following cellulose thin layer electrophoresis in pyridine/acetic acid (pH 4.4), 5 h at 500 V, appropriate areas of the plate are scraped and the dansyl hexosamines are eluted with 95% ethanol. Aliquots are then applied to a silica gel tlc plate and subjected to ascending thin layer chromatography in cyclohexane/ethylacetate/ethanol (6/4/3). After spraying the plate with triethanolamine/isopropanol ($\text{1}\text{4}$), fluorescent intensities are measured by in situ scanning. The aminosugar content of the glycoprotein is determined from a curve generated from a series of standards run concurrently on each plate. The method clearly resolves glucosamine from galactosamine, and is sensitive for the detection of aminosugars in the subnanomole range.     

Immunocytochemical identification of cytoskeletal linkages to smooth muscle cell nuclei and mitochondria

In avian smooth muscle cells, desmin-containing intermediate filaments (IFs) are a prominent component of the cytoskeleton and are readily seen in several domains, including the axial intermediate filament bundle (IFB). Both the nucleus and some of the mitochondria are partly surrounded by elements of the IFB. By using anti-desmin and protein-A-colloidal gold labeling, we have identified intermediate filaments that form linkages with the nuclear envelope and with mitochondria. These linkage regions seem to occupy a proportionately greater part of the mitochondrial surface than of the nuclear envelope. The existence of these linkages in smooth muscle cells is consistent with results that support similar linkages to mitochondria and other cellular structures in various cells that contain either vimentin or keratin IFs. These linkages could functionally restrain or assist in homeostatically restoring organelles to their normal position after the rearrangement that accompanies the substantial shortening of smooth muscle cells.     

水稻可溶性糖蛋白的纯化与鉴定研究

从水稻鲜叶中提取总蛋白,对总蛋白中的蛋白质含量进行了测定;通过硫酸铵沉淀将总蛋白提取液进行分级,从而达到了总蛋白细分和放量的目的。四级份的分级蛋白分别通过ConA-Sepharose 4B 亲和层析进行糖蛋白纯化,按吸收峰收集的各级糖蛋白混合物进行冷冻干燥,得到干粉;结合PAS法染色和考马斯亮蓝R-250染色对四级份的糖蛋白样品鉴定,在其中3个级份中均检测出糖蛋白;由于感度的差异,按考马斯亮蓝R-250染色可检测出近30种糖蛋白(包括部分糖肽),按PAS法染色可检测到7种糖蛋白;对3种含量较高的糖蛋白进行了胶上纯化,3种糖蛋白的PAS法染色均证实了3种样品为单一的糖蛋白或者糖肽,分别命名为RG1、RG2和RG3。