tyvelose and paratose

In the past few years, there have been many important advances in our understanding of the biosynthesis of deoxysugars. Mechanistic studies have shed light on how enzymes can cleave C-O bonds, epimerize the configuration of substituents and reduce keto groups to make deoxysugars. Exciting progress has also been made in our comprehension of the genetics of deoxysugar biosynthesis in antibiotics. All this information is important for potential medical and biotechnological applications, such as drug discovery based on combinatorial biology.

Topics: Deoxyribose; Glycosyltransferases; Hexoses; Saccharopolyspora; Streptomyces

Bacteriophage P22 recognizes O-antigen polysaccharides of Salmonella enterica subsp. enterica (S.) with its tailspike protein (TSP). In the serovars S. Typhimurium, S. Enteritidis, and S. Paratyphi A, the tetrasaccharide repeat units of the respective O-antigens consist of an identical main chain trisaccharide but different 3,6-dideoxyhexose substituents. Here, the epimers abequose, tyvelose and paratose determine the specific serotype. P22 TSP recognizes O-antigen octasaccharides in an extended binding site with a single 3,6-dideoxyhexose binding pocket. We have isolated S. Paratyphi A octasaccharides which were not available previously and determined the crystal structure of their complex with P22 TSP. We discuss our data together with crystal structures of complexes with S. Typhimurium and S. Enteritidis octasaccharides determined earlier. Isothermal titration calorimetry showed that S. Paratyphi A octasaccharide binds P22 TSP less tightly, with a difference in binding free energy of ∼7 kJ mol(-1) at 20°C compared with S. Typhimurium and S. Enteritidis octasaccharides. Individual protein-carbohydrate contacts were probed by amino acid replacements showing that the dideoxyhexose pocket contributes to binding of all three serotypes. However, S. Paratyphi A octasaccharides bind in a conformation with an energetically unfavorable ϕ/ψ glycosidic bond angle combination. In contrast, octasaccharides from the other serotypes bind as solution-like conformers. Two water molecules are conserved in all P22 TSP complexes with octasaccharides of different serotypes. They line the dideoxyhexose binding pocket and force the S. Paratyphi A octasaccharides to bind as nonsolution conformers. This emphasizes the role of solvent as part of carbohydrate binding sites.

Topics: Amino Acid Sequence; Bacteriophage P22; Binding Sites; Carbohydrate Conformation; Carbohydrate Sequence; Glycoside Hydrolases; Hexoses; Molecular Docking Simulation; Molecular Sequence Data; Mutation; O Antigens; Protein Binding; Salmonella paratyphi A; Viral Tail Proteins

Extensive variations of the ring structures of three deoxyaldohexopyranoses, L-fucose, D-quinovose, and L-rhamnose, and four dideoxyaldohexopyranoses, D-digitoxose, abequose, paratose, and tyvelose, were studied by energy minimization with the molecular mechanics algorithm MM3(92). Chair conformers, 4C(1) in D-quinovose and the equivalent 1C(4) in L-fucose and L-rhamnose, overwhelmingly dominate in the three deoxyhexoses; in the D-dideoxyhexoses, 4C(1) is again dominant, but with increased amounts of 1C(4) forms in the alpha anomers of the three 3,6-dideoxyhexoses, abequose, paratose, and tyvelose and in both alpha and beta anomers of the 2,6-dideoxyhexose D-digitoxose. In general, modeled proton-proton coupling constants agreed well with experimental values. Computed anomeric ratios strongly favor the beta configuration except for D-digitoxose, which is almost equally divided between alpha and beta configurations, and L-rhamnose, where the beta configuration is somewhat favored. MM3(92) appears to overstate the prevalence of the equatorial beta anomer in all three deoxyhexoses, as earlier found with fully oxygenated aldohexopyranoses.

Topics: Algorithms; Carbohydrate Conformation; Deoxy Sugars; Deoxyglucose; Fucose; Hexoses; Magnetic Resonance Spectroscopy; Models, Molecular; Rhamnose; Software; Thermodynamics

Preparations of ascarylose (3,6-dideoxy-L-arabino-hexose), abequose (3,6-dideoxy-D-xylo-hexose), and paratose (3,6-dideoxy-D-ribo-hexose) with stereospecific deuterium labeling at C-3 are discussed. The methods used to synthesize these sugars, such as the hydrogenation of olefins, the displacement of halides, the reduction of epoxides, and the substitution of tosyl esters, illustrate a variety of strategies leading to stereospecific deuterium incorporation. Many of the techniques described here should be of general utility for the synthesis of other deuterium-labeled sugars.

Topics: Carbohydrate Conformation; Deuterium; Hexoses; Isotope Labeling; Magnetic Resonance Spectroscopy; Reference Standards; Stereoisomerism