The conformational flexibility of methyl α-cellobioside in water and dimethyl sulfoxide solutions was investigated by 1D 1H,1H T-ROESY experiments. In combination with molecular dynamics simulat ...

The three-dimensional structure of a cyclic enterobacterial common antigen (ECA) having four trisaccharide repeating units has been investigated by NMR spectroscopy and molecular dynamics simulations. Three different NMR parameters were determined: (a) (1)H,(1)H cross-relaxation rates from NOE experiments were used for determination of proton-proton distances; (b) trans-glycosidic (3)J(C,H) scalar coupling constants analyzed via a Karplus-type relationship provided information on torsion angles; and (c) (1)H,(13)C one-bond dipolar couplings obtained in a dilute liquid-crystalline medium were interpreted in terms of the orientational order and molecular conformations. The molecular dynamics simulations of the dodecasaccharide were performed with explicit water and counterions, which are important factors that strongly influence molecular conformation. Subsequently, the results from computer simulation were used to generate a three-dimensional structure of the cyclic ECA which is consistent with the experimental NMR parameters.

A viscous extracellular polysaccharide produced by Lactobacillus helveticus Lb161 isolated from raw milk has been investigated. Sugar and methylation analysis, and 1H and 13C NMR spectroscopy revealed that the polysaccharide is composed of a heptasaccharide repeating unit. The sequence of sugar residues was determined by use of two-dimensional nuclear Overhauser effect spectroscopy and heteronuclear multiple bond connectivity experiments. The structure of the repeating unit of the exopolysaccharide from L. helveticus Lb161 is as follows: carbohydrate structure [see text]. The polysaccharide contains approximately 0.6 equivalents of O-acetyl group per repeating unit (not located).

A viscous extracellular polysaccharide produced by Lactobacillus helveticus K16 has been investigated. Sugar and methylation analysis, H-1 and C-13 NMR spectroscopy revealed that the polysaccharide is composed of a hexasaccharide repeating unit. The sequence of sugar residues was determined by use of two-dimensional nuclear Overhauser effect spectroscopy and heteronuclear multiple bond connectivity experiments. The structure of the repeating unit of the exopolysaccharide from L. helveticus K16 is as follows:[GRAPHICS](C) 2000 Elsevier Science Ltd. All rights reserved.

Five slime-forming Lactococcus lactis ssp. cremoris strains (ARH53, ARH74, ARH84, ARH87 and B30) isolated from Finnish fermented milk viili have been shown to produce viscous exopolysaccharides (EPSs) in skim milk cultures. The EPSs were separated and purified by treatment with trichloroacetic acid, ethanol precipitation and dialysis. All EPSs were anionic and composed of galactose, glucose and rhamnose of similar ratios. The 1H NMR spectrum of the EPS of strain ARH 74 showed high similarity with that of strain SBT 0495 EPS, previously reported to consist of pentasaccharide repeating units with a phosphodiester structural element. In dilute aqueous solutions (up to 0.1 g dl−1 of EPS), the EPSs showed polyelectrolyte effects, and they differed in viscosity. At a higher concentration of EPS (1%, w/v), the EPS solution showed a shear thinning behaviour, and the viscosity was temperature, pH and salt dependent. Addition of 1% EPS (w/v) to skim milk resulted in a significant increase in viscosity, and a gel formed at 40°C.

The structure of the O‐antigen polysaccharide of the lipopolysaccharide from an enteroaggregative Escherichia coli (strain 105) has been elucidated, using primarily one‐dimensional and two‐dimensional NMR experiments. The sequence of residues was deduced with heteronuclear multiple‐bond correlation and NOESY experiments. The structure of the repeating unit of the polysaccharide from the enteroaggregative E. coli is as follows:The structure of the O‐antigen from enteroaggregative E. coli strain 105 was shown to be identical with that of E. coli O21 by sugar and methylation analyses as well as by 1H‐NMR and 13C‐NMR spectroscopy.

The O‐antigen polysaccharide of the lipopolysaccharide from the enteroaggregative Escherichia coli strain 62D1 has been determined. Sugar and methylation analysis together with 1H and 13C NMR spectroscopy revealed the components of the repeating unit. Two‐dimensional NOESY and heteronuclear multiple‐bond correlation experiments were used to deduce the sequence. 1H and 13C NMR spectra indicate heterogeneity in the polysaccharide. Methylation analysis and 1H NMR spectra of native and Smith‐degraded material show that the majority (65%) of the repeating units has the following structure:Minor resonances in the NMR spectra are consistent with the presence of repeating units which lack the α‐d‐Galp terminal residue (35%).

The structure of the O‐antigen polysaccharide of the lipopolysaccharide from the enteroinvasive Escherichia coli O136 has been elucidated. The composition of the repeating unit was established by sugar and methylation analysis together with 1H and 13C NMR spectroscopy. Two‐dimensional nuclear Overhauser effect spectroscopy (NOESY) and heteronuclear multiple‐bond correlation experiments were used to deduce the sequence. The absolute configuration for the nonulosonic acid (NonA) could be determined using spin‐spin coupling constants, 13C chemical shifts and NOESY. The anomeric configuration of the NonA was determined via vicinal and geminal 13C,1H coupling constants. The structure of the repeating unit of the polysaccharide from E. coli O136 is as follows, in which β‐NonpA is 5,7‐diacetamido‐3,5,7,9‐tetradeoxy‐lglycero‐β‐lmanno‐nonulosonic acid:→4)‐β‐NonpA‐(2→4)‐β‐d‐Galp‐(1→4)‐β‐d‐GlcpNAc‐(1→

The O-antigenic polysaccharide of the lipopolysaccharide from the enterotoxigenic Escherichia coli O101 has been investigated. The composition and sequence of the repeating units was established by sugar and methylation analysis together with 1H and 13C NMR spectroscopy. The sequence was corroborated using the computer program CASPER. The structure of the repeating unit of the polysaccharide from E. coli O101 is as follows: -->6)-alpha-D-GlcpNAc-1-->4-alpha-D-GalpNAc-(1-->.

The O‐antigen polysaccharide of the lipopolysaccharide from the enteroaggregative Escherichia coli O44:H18 has been investigated. Sugar and methylation analysis, 1H‐ and 13C‐NMR spectroscopy revealed that the polysaccharide is composed of pentasaccharide repeating units. The sequence of sugar residues was determined by use of two‐dimensional nuclear Overhauser effect spectroscopy and heteronuclear multiple bond correlation experiments. The structure of the repeating unit of the O‐antigen from Escherichia coli O44:H18 is as follows. image