RESUMO
The exopolysaccharide produced by Streptococcus thermophilus 8S in reconstituted skimmed milk is a heteropolysaccharide containing d-galactose, d-glucose, d-ribose, and N-acetyl-d-galactosamine in a molar ratio of 2 : 1 : 1 : 1. Furthermore, the polysaccharide contains one equivalent of a novel open chain nononic acid constituent, 3,9-dideoxy-d-threo-d-altro-nononic acid, ether-linked via C-2 to C-6 of an additional d-glucose per repeating unit. Methylation analysis and 1D/2D NMR studies (1H and 13C) performed on the native polysaccharide, and mass spectrometric and NMR analyses of the oligosaccharide obtained from the polysaccharide by de-N-acetylation followed by deamination and reduction demonstrated the 'hepta'saccharide repeating unit to be: -->4)-alpha-D-Galp-(1-->2)-beta-D-Ribf-(1-->4)-beta-D-Galp-(1-->4)-beta-D-Glcp-(1--7')-Sub-(1-->4)-beta-D-GalpNAc-(1--> in which Sug is 6-O-(3',9'-dideoxy-d-threo-d-altro-nononic acid-2'-yl)-alpha-d-glucopyranose.
Assuntos
Polissacarídeos Bacterianos/química , Streptococcus/química , Sequência de Carboidratos , Cromatografia Gasosa , Ácido Láctico/metabolismo , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Metilação , Modelos Químicos , Dados de Sequência Molecular , Monossacarídeos/química , Polissacarídeos/química , Polissacarídeos/metabolismo , Açúcares Ácidos/químicaRESUMO
A novel sugar constituent was isolated from the heteropolysaccharide excreted by Streptococcus thermophilus 8 S when grown in skimmed milk. The structure and absolute configuration were determined by means of chemical analysis, mass spectrometry, NMR spectroscopy, along with molecular dynamics simulations, and was shown to be 6-O-(3',9'-dideoxy-D-threo-D-altro-nononic acid-2'-yl)-D-glucopyranose.
Assuntos
Éteres/química , Glucose/química , Polissacarídeos/química , Streptococcus/química , Ácidos/química , Configuração de Carboidratos , Modelos Moleculares , Ressonância Magnética Nuclear Biomolecular , Polissacarídeos/isolamento & purificação , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por MatrizRESUMO
A method is described for constructing a conformational model in water of a heteropolysaccharide built up from repeating units, and is applied to the exopolysaccharide produced by Lactobacillus helveticus 766. The molecular modeling method is based on energy minima, obtained from molecular mechanics calculations of each of the constituting disaccharide fragments of the repeating unit in vacuo, as starting points. Subsequently, adaptive umbrella sampling of the potential of mean force is applied to extract rotamer populations of glycosidic dihedral angles of oligosaccharide fragments in solution. From these analyses, the most probable conformations are constructed for the hexasaccharide-repeating unit of the polysaccharide. After exploring the conformational space of each of the individual structures by molecular dynamics simulations, the different repeating unit conformations are used as building blocks for the generation of oligo- and polysaccharide models, by using a polysaccharide building program. The created models of the exopolysaccharide produced by L. helveticus 766 exhibit a flexible twisted secondary structure and tend to adopt a random coil conformation as tertiary structure.
