Yasunori Isshiki

Galectins are β-galactoside-binding animal lectins involved in various biological functions, such as host defense. Galectin-2 and -3 are members of the galectin family that are expressed in the stomach, including the gastric mucosa and surface mucous cells. Galectin-3 exhibits aggregation and bactericidal activity against Helicobacter pylori in a β-galactoside-dependent manner. We previously reported that galectin-2 has the same activity under neutral pH conditions. In this study, the H. pylori aggregation activity of galectin-2 was examined under weakly acidic conditions, in which H. pylori survived. Galectin-2 agglutinated H. pylori even at pH 6.0, but not at pH 5.0, correlating with its structural stability, as determined using circular dichroism. Additionally, galectin-2 binding to the lipopolysaccharide (LPS) of H. pylori cultured under weakly acidic conditions was investigated using affinity chromatography and Western blotting. Galectin-2 could bind to H. pylori LPS containing H type I, a Lewis antigen, in a β-galactoside-dependent manner. In contrast, galectin-3 was structurally more stable than galectin-2 under acidic conditions and bound to H. pylori LPS containing H type I and Lewis X. In conclusion, galectin-2 and -3 might function cooperatively in the defense against H. pylori in the stomach under different pH conditions.

Structural characterization studies have been carried out on the carbohydrate backbone of Vibrio parahaemolyticus serotype O6 lipopolysaccharides (LPS). The carbohydrate backbone isolated from O6 LPS by sequential derivatization, that is, dephosphorylation, O-deacylation, pyridylamination, N-deacylation and N-acetylation, is a nonasaccharide consisting of 3 mol of D-glucosamine (GlcN) (of which one is pyridylaminated), 2 mol of L-glycero-D-manno-heptose (Hep), and 1 mol each of D-galactose (Gal), D-glucose (Glc), D-glucuronic acid (GlcA) and 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo). Structural analyses by nuclear magnetic resonance spectroscopy and fast-atom bombardment mass spectrometry demonstrated that the carbohydrate backbone is β-Galp-(1→2)-α-Hepp-(1→3)-α-Hepp-(1→5)-α-Kdop-(2→6)-β-GlcpNAc-(1→6)-GlcNAc-PA, in which the 3-substituted α-Hepp is further substituted by β-GlcpNAc-(1→4)-β-Glcp at position 4 and by β-GlcpA at position 2. In native O6 LPS, an additional 1 mol of D-galacturonic acid, which is liberated by dephosphorylation in hydrofluoric acid, is present at an unknown position. A previous study by the present authors reported that, of 13 O-serotype LPS of V. parahaemolyticus, the only LPS from which Kdo was detected was from O6 LPS after mild acid hydrolysis. In the present study, we have demonstrated that only 1 mol of Kdo is present at the lipid A proximal position, a component which is common to the LPS in all serotypes of the bacterium, and that there is no additional Kdo in the carbohydrate backbone of O6 LPS. ELISA and ELISA inhibition analysis using antisera against O6 and Salmonella enterica Minnesota R595 and LPS of both strains further revealed that Kdo is not involved as an antigenic determinant of O6 LPS.