Metabolic Profiling of Xylooligosaccharides by Lactobacilli

Three lactic acid bacteria (LAB) strains identified as Lactobacillus plantarum, Lactobacillus brevis, and Lactobacillus sakei isolated from meat products were tested for their ability to utilize and grow on xylooligosaccharides (XOSs). The extent of carbohydrate utilization by the studied strains was analyzed by HPLC. All three strains showed preferences for the degree of polymerization (DP). The added oligosaccharides induced the LAB to form end-products of typical mixed-acid fermentation. The utilization of XOSs by the microorganisms requires the action of three important enzymes: β-xylosidase (EC 3.2.1.37) exo-oligoxylanase (EC 3.2.1.156) and α-L-arabinofuranosidase (EC 3.2.1.55). The presence of intracellular β-D-xylosidase in Lb. brevis, Lb. plantarum, and Lb. sakei suggest that XOSs might be the first imported into the cell by oligosaccharide transporters, followed by their degradation to xylose. The studies on the influence of XOS intake on the lipids of rat liver plasma membranes showed that oligosaccharides display various beneficial effects for the host organism, which are probably specific for each type of prebiotic used. The utilization of different types of oligosaccharides may help to explain the ability of Lactobacillus strains to compete with other bacteria in the ecosystem of the human gastrointestinal tract.

Evidence for regulated dimerization of cell-cell adhesion molecule (C-CAM) in epithelial cells

C-CAM is a Ca2+-independent cell adhesion molecule (CAM) belonging to the immunoglobulin superfamily. Addition of chemical cross-linkers to isolated rat liver plasma membranes, intact epithelial cells and purified preparations of C-CAM stabilized one major C-CAM-containing product whose apparent molecular mass was approximately twice that of the C-CAM monomer. The failure to detect additional proteins after cleavage of the cross-linked species demonstrated that C-CAM exists as non-covalently linked dimers both in solution and on the cell surface. Dimerization occurred to the same extent in adherent monolayers and in single cell populations, indicating that dimer formation was the result of cis- interactions within the membranes of individual cells. Using isoform-specific anti-peptide antibodies, both C-CAM1 and C-CAM2 were found to be involved in dimerization, forming predominantly homo-dimeric species. Both calmodulin and Ca2+ ionophore modulated the level of dimer formation, suggesting a role for regulated self-association in the functional activity of C-CAM.