Oligosaccharide Motifs Research Articles

Distribution of pectic epitopes in cell walls of the sugar beet root

Immunolabelling techniques with antibodies specific to partially methyl-esterified homogalacturonan (JIM5: unesterified residues flanked by methylesterified residues. JIM7: methyl-esterified residues flanked by unesterified residues), a blockwise de-esterified homogalacturonan (2F4), 1,4-galactan (LM5) and 1,5-arabinan (LM6) were used to map the distribution of pectin motifs in cell walls of sugar beet root (Beta vulgaris). PME and alkali treatments of sections were used in conjunction with JIM5-7 and 2F4. The JIM7 epitope was abundant and equally distributed in all cells. In storage parenchyma, the JIM5 epitope was restricted to some cell junctions and the lining of intercellular spaces while in vascular tissues it occurred at cell junctions in some phloem walls and in xylem derivatives. After secondary wall formation, the JIM5 epitope was restricted to inner cell wall regions between secondary thickenings. The 2F4 epitope was not detected without de-esterification treatment. PME treatments prior to the use of 2F4 indicated that HG at cell corners was not acetylated. The LM5 epitope was mainly present in the cambial zone and when present in storage parenchyma, it was restricted to the wall region closest to the plasma membrane. The LM6 epitope was widely distributed throughout primary walls but was more abundant in bundles than in medullar ray tissue and storage parenchyma. These data show that the occurrence of oligosaccharide motifs of pectic polysaccharides are spatially regulated in sugar beet root cell walls and that the spatial patterns vary between cell types suggesting that structural variants of pectic polymers are involved in the modulation of cell wall properties.

Nitrogen-fixing bacterium Burkholderia brasiliensis produces a novel yersiniose A-containing O-polysaccharide

Burkholderia brasiliensis, a Gram-negative diazotrophic endophytic bacterium, was first isolated from roots, stems, and leaves of rice plant in Brazil. The polysaccharide moiety was released by ammonolysis from the B. brasiliensis lipopolysaccharide (LPS), allowing the unambiguous characterization of a 3,6-dideoxy-4-C-(1-hydroxyethyl)-D-xylo-hexose (yersiniose A), an uncommon feature for Burkholderia LPS. The complete structure of the yersiniose A-containing O-antigen was identified by sugar and methylation analyses and NMR spectroscopy. Our results show that the repeating oligosaccharide motif of LPS O-chain consists of a branched tetrasaccharide with the following structure:-->2-alpha-d-Rhap-(1-->3)-[alpha-YerAp-(1-->2)]-alpha-D-Rhap-(1-->3)-alpha-D-Rhap-(1-->.

Effect of iodide on nicotinamide adenine dinucleotide phosphate oxidase activity and Duox2 protein expression in isolated porcine thyroid follicles.

Thyroperoxidase requires H(2)O(2) to catalyze the biosynthesis of thyroxine residues on thyroglobulin. Iodide inhibits the generation of H(2)O(2), and consequently the synthesis of thyroid hormones (Wolff-Chaikoff effect). The H(2)O(2) generator is a calcium-dependent nicotinamide adenine dinucleotide phosphate (NADPH) oxidase involving the flavoprotein Duox2. NADPH oxidase activity and Duox2 require cAMP to be expressed in pig thyrocytes. We studied the effect of iodide on NADPH oxidase activity, the DUOX2 gene, and Duox2 protein expression in pig thyroid follicles cultured for 48 h with forskolin or a cAMP analog. Iodide inhibited the cellular release of H(2)O(2) and NADPH oxidase activity, effects prevented by methimazole. Northern blot studies showed that iodide did not reduce DUOX2 mRNA levels but did reduce those of TPO and NIS. Western blot analyses using a Duox2-specific antipeptide showed that Duox2 has two N-glycosylation states, which have oligosaccharide motifs accounting for about 15 kDa and 25 kDa, respectively, of the apparent molecular mass. Cyclic AMP increased the amount of the highly glycosylated form of Duox2, an effect antagonized by iodide in a methimazole-dependent manner. These data suggest that an oxidized form of iodide inhibits the H(2)O(2) generator at a posttranscriptional level by reducing the availability of the mature Duox2 protein.

Thermodynamic Studies of Saccharide Binding to Artocarpin, a B-Cell Mitogen, Reveals the Extended Nature of Its Interaction with Mannotriose [3,6-Di-O-(α-d-mannopyranosyl)-d-mannose

The thermodynamics of binding of various saccharides to artocarpin, from Artocarpus integrifolia seeds, a homotetrameric lectin (M(r) 65, 000) with one binding site per subunit, was determined by isothermal titration calorimetry measurements at 280 and 293 K. The binding enthalpies, DeltaH(b), are the same at both temperatures, and the values range from -10.94 to -47.11 kJ mol(-1). The affinities of artocarpin as obtained from isothermal titration calorimetry are in reasonable agreement with the results obtained by enzyme-linked lectin absorbent essay, which is based on the minimum amount of ligand required to inhibit horseradish peroxidase binding to artocarpin in enzyme-linked lectin absorbent essay (Misquith, S., Rani, P. G., and Surolia, A. (1994) J. Biol. Chem. 269, 30393-30401). The interactions are mainly enthalpically driven and exhibit enthalpy-entropy compensation. The order of binding affinity of artocarpin is as follows: mannotriose>Manalpha3Man>GlcNAc(2)Man(3)>MealphaMan>Man>M analpha6Man> Manalpha2Man>MealphaGlc>Glc, i.e. 7>4>2>1.4>1>0.4>0.3>0.24>0.11. The DeltaH for the interaction of Manalpha3Man, Manalpha6Man, and MealphaMan are similar and 20 kJ mol(-1) lower than that of mannotriose. This indicates that, while Manalpha3Man and Manalpha6Man interact with the lectin exclusively through their nonreducing end monosaccharide with the subsites specific for the alpha1,3 and alpha1,6 arms, the mannotriose interacts with the lectin simultaneously through all three of its mannopyranosyl residues. This study thus underscores the distinction in the recognition of this common oligosaccharide motif in comparison with that displayed by other lectins with related specificity.