Isomalto-oligosaccharide-containing lipoteichoic acid of Streptococcus sanguis. Microheterogeneity and distribution of chain substituents

Rutin Prevents LTA Induced Oxidative Changes in H9c2 Cells

Lipoteichoic acid (LTA), a component of Gram-positive bacteria cell walls is involved in infective endocarditis (IE), a life-threatening disease. We evaluated for the first time, whether flavonoid rutin (quercetin-3-rutinoside) can block LTA-induced pro-inflammatory response and reactive oxygen species (ROS) production, and reduction of antioxidant enzymes. We found that rutin suppresses LTA effects on the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase, as well as the pro-inflammatory enzyme cyclooxygenase-2, preventing phosphorylation of the mitogen-activated protein kinases (MAPKs), p38, and c-Jun N-terminal kinase, and the increase of ROS production induced by LTA. Taken together, these findings suggest that rutin prevents oxidative damage, inflammation, and MAPKs activation induced by LTA. Rutin may exert a protective effect in IE. These data provide novel insights for future use of rutin to prevent the mechanisms of LTA-related pathogenesis, inflammatory processes, and antioxidant enzyme levels in diseases such as IE.

Genome-wide essential gene identification in Streptococcus sanguinis

A clear perception of gene essentiality in bacterial pathogens is pivotal for identifying drug targets to combat emergence of new pathogens and antibiotic-resistant bacteria, for synthetic biology, and for understanding the origins of life. We have constructed a comprehensive set of deletion mutants and systematically identified a clearly defined set of essential genes for Streptococcus sanguinis. Our results were confirmed by growing S. sanguinis in minimal medium and by double-knockout of paralogous or isozyme genes. Careful examination revealed that these essential genes were associated with only three basic categories of biological functions: maintenance of the cell envelope, energy production, and processing of genetic information. Our finding was subsequently validated in two other pathogenic streptococcal species, Streptococcus pneumoniae and Streptococcus mutans and in two other gram-positive pathogens, Bacillus subtilis and Staphylococcus aureus. Our analysis has thus led to a simplified model that permits reliable prediction of gene essentiality.

Semisynthetic hydrophilic polyals

Non-bioadhesive, fully biodegradable soluble polymers would be very instrumental in advanced biomedical applications, such as gene and drug delivery and tissue engineering. However, rational development of such materials is hindered by the complexity of macromolecule interactions with biological milieu. The prevalence of carbohydrates in naturally occurring interface structures suggests an alternative, biomimetic approach. Interface carbohydrates, regardless of their biological function, have common non-signaling substructures (e.g., acetal and ketal groups, secondary and primary alcohols). We hypothesized that hydrophilic polymers (polyals) consisting of acyclic units built of non-signaling carbohydrate substructures would be highly biocompatible and non-bioadhesive, while intrachain acetal or ketal groups would enable nonenzymatic biodegradation upon uptake by cells. Acyclic hydrophilic polyals can be prepared via either polymerization of suitable monomers or lateral cleavage of cyclic polyals (e.g., polysaccharides). In this study, model polyals were produced via lateral cleavage of polyaldoses and polyketoses. Best results were achieved using dextran B-512 as a precursor. The resultant poly[hydroxymethylethylene hydroxymethylformal], in agreement with the hypothesis, demonstrated excellent biological properties and technological flexibility. Materials of this type can potentially have several applications in pharmacology and bioengineering.

Unique poly(glycerophosphate) lipoteichoic acid and the glycolipids of a Streptococcus sp. closely related to Streptococcus pneumoniae

The Streptococcus sp. studied here is closely related to Streptococcus pneumoniae with 98.6% 16S rRNA similarity and 65% DNA/DNA homology. We isolated the lipoteichoic acid and the membrane glycolipids whose structures were established using conventional procedures and NMR spectroscopy. The lipoteichoic acid contains a linear 1,3-linked poly(glycerophosphate) chain which is partly substituted with D-alanine ester and is phosphodiester-linked to O6 of beta-D-Galf(1-->3)acyl2Gro. This lipoteichoic acid is the first example in which a monohexosylglycerol serves as the glycolipid anchor; and with an average chain length of 10 glycerophosphate residues it is the shortest known to date. MS analysis, applied for the first time to a native acylated lipoteichoic acid, revealed a continuous increase in chain length from seven to 17 glycerophosphate residues with a maximum at 10, and allowed identification of the fatty acid combinations. Membrane glycolipids consisted of beta-D-Galf(1-->3)acyl2Gro (9%), alpha-D-Glcp(1-->3)acyl2Gro (22%), alpha-D-Galp(1-->2)-alpha-D-Glcp(1-->3)acyl2Gro (64%) and alpha-D-Galp(1-->2)-(6-O-acyl)-alpha-D-Glcp(1-->3)acyl2Gro (5%). It is noteworthy that in lipoteichoic acid biosynthesis, Galfacyl2Gro, a less abundant membrane glycolipid, is selected as the lipid anchor. Despite the genetic relatedness to Streptococcus pneumoniae, the lipoteichoic acid structure is quite different to the complex structure of pneumococcal lipoteichoic acid [T. Behr et al. (1992) Eur. J. Biochem. 207, 1063-1075], thus providing an example that minor differences in DNA sequence exert major changes in macromolecular structure.

Competitive binding of calcium and magnesium to streptococcal lipoteichoic acid

Equilibrium dialysis was used to investigate the binding capacity and affinity of lipoteichoic acid (LTA) from the Gram-positive bacterium Streptococcus sanguis for calcium and magnesium by a competitive method. LTA was shown to bind approx. 1 mol of either calcium or magnesium per mole phosphate. Calcium and magnesium dissociation constants were found to be 8.39 +/- 0.31 mmol/l and 15.01 +/- 2.01 mmol/l respectively, indicating that S. sanguis LTA will preferentially bind calcium. LTA may act as a calcium buffer by reducing the free calcium concentration to which the cell is exposed. The capacity to produce large quantities of LTA could thus be as important as aciduricity in selection of species at caries-prone sites.