Characterization of glycosaminoglycan (GAG) sulfatases from the human gut symbiont Bacteroides thetaiotaomicron reveals the first GAG-specific bacterial endosulfatase.

Despite the importance of the microbiota in human physiology, the molecular bases that govern the interactions between these commensal bacteria and their host remain poorly understood. We recently reported that sulfatases play a key role in the adaptation of a major human commensal bacterium, Bacteroides thetaiotaomicron, to its host (Benjdia, A., Martens, E. C., Gordon, J. I., and Berteau, O. (2011) J. Biol. Chem. 286, 25973-25982). We hypothesized that sulfatases are instrumental for this bacterium, and related Bacteroides species, to metabolize highly sulfated glycans (i.e. mucins and glycosaminoglycans (GAGs)) and to colonize the intestinal mucosal layer. Based on our previous study, we investigated 10 sulfatase genes induced in the presence of host glycans. Biochemical characterization of these potential sulfatases allowed the identification of GAG-specific sulfatases selective for the type of saccharide residue and the attachment position of the sulfate group. Although some GAG-specific bacterial sulfatase activities have been described in the literature, we report here for the first time the identity and the biochemical characterization of four GAG-specific sulfatases. Furthermore, contrary to the current paradigm, we discovered that B. thetaiotaomicron possesses an authentic GAG endosulfatase that is active at the polymer level. This type of sulfatase is the first one to be identified in a bacterium. Our study thus demonstrates that bacteria have evolved more sophisticated and diverse GAG sulfatases than anticipated and establishes how B. thetaiotaomicron, and other major human commensal bacteria, can metabolize and potentially tailor complex host glycans.

NMR study on the interaction of trehalose with lactose and its effect on the hydrogen bond interaction in lactose.

Trehalose, a well-known stress-protector of biomolecules, has been investigated for its effect on the mobility, hydration and hydrogen bond interaction of lactose using diffusion-ordered NMR spectroscopy and NMR of hydroxy protons. In ternary mixtures of trehalose, lactose and water, the two sugars have the same rate of diffusion. The chemical shifts, temperature coefficients, vicinal coupling constants and ROE of the hydroxy protons in trehalose, lactose and sucrose were measured for the disaccharides alone in water/acetone-d6 solutions as well as in mixtures. The data indicated that addition of trehalose did not change significantly the strength of the hydrogen bond interaction between GlcOH3 and GalO5' in lactose. Small upfield shifts were however measured for all hydroxy protons when the sugar concentration was increased. The chemical shift of the GlcOH3 signal in lactose showed less change, attributed to the spatial proximity to GalO5'. Chemical exchange between hydroxy protons of lactose and trehalose was observed in the ROESY NMR spectra. Similar effects were observed with sucrose indicating no specific effect of trehalose at the concentrations investigated (73 to 763 mg/mL) and suggesting that it is the concentration of hydroxy groups more than the type of sugars which is guiding intermolecular interactions.

Application of diffusion-edited NMR spectroscopy for selective suppression of water signal in the determination of monomer composition in alginates.

Alginate is a linear copolymer of 1-4 linked ß-D-mannuronic acid (M) and 1-4 linked α-L-guluronic acid (G). The physical properties of these polysaccharides such as gel properties and viscosity are largely correlated to the monomer composition (M/G ratio), the sequence of the polymer and the molecular weight. Determination of the M/G ratio is therefore important and NMR spectroscopy is among the most common methods used to accurately obtain this ratio. Instead of using time consuming, possibly sample altering, acid hydrolysis to reduce the viscosity of the alginate sample prior to analysis, samples of low concentrations can be used. However, this results in a water peak in the NMR spectrum that is several orders of magnitude larger than the alginate signals and water suppression is required. In this article, a diffusion-edited NMR experiment that suppresses the water peak while retaining the signals of interest has been used to enable correct M/G ratio determination. This approach exploits the difference in translational diffusion between the larger alginate molecules and the smaller water molecules. Using this method, the monomer composition of 20 different alginate powders was determined. The diffusion parameters were optimized to allow measurement for samples covering a large range of M/G ratios and viscosities. Thus, such method should be useful for analyzing large numbers of unknown alginate samples using, for example, automation procedures.

NMR study on hydroxy protons of κ- and κ/µ-hybrid carrageenan oligosaccharides: experimental evidence of hydrogen bonding and chemical exchange interactions in κ/µ oligosaccharides.

The hydroxy protons of κ- and κ/µ-hybrid carrageenan oligosaccharides have been studied by NMR spectroscopy in 85% H(2)O/15% acetone-d(6). Hydration and hydrogen bonding interactions in di- (κ), tetra- (κκ), hexa (κκκ), and octa- (κκκκ) κ-oligosaccharides and hexa- (κµκ), octa- (κµµκ), and deca- (κµµµκ) κ/µ-oligosaccharides have been investigated by measuring the chemical shifts, temperature coefficients, and chemical exchange of the hydroxy protons. These NMR parameters indicate that no strong and persistent intramolecular hydrogen bonds involving hydroxy protons stabilize the structure of κ-carrageenan oligosaccharides in aqueous solution. In the κ/µ-oligosaccharides, the presence of chemical exchange between OH3 of α-d-Gal-6-sulfate (D6S) and OH2 of ß-d-Gal-4-sulfate (G4S) across the ß-d-Gal-4-S-(1→4)-α-d-Gal-6-S linkage reveals the existence of a weak hydrogen bond interaction between the two hydroxyl groups. The smaller temperature coefficients of OH2_D6S and OH3_D6S indicate reduced hydration, interpreted as spatial proximity to the 4-sulfate group and O5 ring oxygen of the neighboring G4S residues, respectively. These first experimental results on the conformation of κ/µ-carrageenan oligosaccharides shine light on the potential role of "kinks" in the properties of the three-dimensional carrageenan gel network.