Bacterial polysaccharide capsule synthesis, export and evolution of structural diversity

Elaboration of a capsule composed of one of a range of acidic polysaccharides is a common feature of many bacteria, particularly those capable of causing serious infections in humans. Biochemical and genetical analyses of capsule biogenesis in Escherichia coli are beginning to reveal new aspects of polysaccharide biosynthesis. Genes have been identified which are thought to encode products responsible for the translocation of these high molecular-weight polysaccharides across the cytoplasmic and outer membranes, and the organization of exported polysaccharide into a capsule. Their further analysis should provide new insights into membrane biology, particularly since the genes in question are absent from the often used laboratory strains of E. coli. Genetic analysis of capsule diversity is beginning to suggest possible mechanisms for the generation of the structural diversity of polysaccharides.     

The capsular (K51) antigen of Escherichia coli 01:K51:H−, an O-acetylated poly-N-acetylglucosamine phosphate

Abstract The capsular K51 antigen of E.coli was isolated from a liquid culture of E.coli 01:K51:H⁻ by Cetavlon precipitation. After purification it was obtained in a yield of about 80 mg/l. The polymer consisted of equimolar amounts of N -acetylglucosamine and phosphate and contained about 1.6 O -acetyl groups per N -acetylglucosamine residue. After de- O -acetylation it was resistant to periodate oxidation. Mild acid hydrolysis yielded N -acetylglucosamine-3-phosphate. With the aid of ¹³C- and ³¹P-NMR spectroscopy it was ascertained that the K51 antigen is a poly- α -1.3- N -acetylglucosamine phosphate, in which most of the hydroxyl groups at C4 and C6 of the N -acetylglucosamine residue are acetylated.     

ON THE MECHANISM OF OUABAIN INHIBITION OF SYNAPTOSOME PROTEIN SYNTHESIS

Abstract— Ouabain (200μ m ) inhibited incorporation of radiolabelled leucine or glycine into the protein of neonatal synaptosome fractions but had minimal effect on preparations from adult rats. Leucine uptake into synaptosomes was rapid but not influenced by 200μ m -ouabain in contrast to ouabain inhibition of [¹⁴C]glycine and [¹⁴C]γ-aminobutyric acid uptake. Ouabain blocked the Na⁺ -dependent (stimulated) component of synaptosome fraction protein synthesis in the presence of 25m m -K⁺. Ouabain inhibition was not alleviated by addition of ADP or ATP. 100μ m -atractylate failed to influence [³H]leucine uptake or incorporation. Synergistic inhibition by ouabain was observed with the cycloheximide-sensitive component of protein synthesis and the chloramphenicol sensitive phase. Increasing the medium Ca²⁺ concentration stimulated protein synthesis and this stimulated component was inhibited by ouabain. Ouabain inhibition was associated with decreasing intraterminal K⁺ concentration and [K]_i was linearly related to the protein synthesis rate in control and ouabain treated preparations.