Otto Holst

Characterization of a Novel Branched Tetrasaccharide of 3-Deoxy-d-manno-oct-2-ulopyranosonic Acid THE STRUCTURE OF THE CARBOHYDRATE BACKBONE OF THE LIPOPOLYSACCHARIDE FROM ACINETOBACTER BAUMANNII STRAIN NCTC 10303 (ATCC 17904)

u2003For the first time, the tetrasaccharide Kdoα2→5Kdoα2→5(Kdoα2→4)Kdo (Kdo is 3-deoxy-d-manno-oct-2-ulopyranosonic acid) has been identified in a bacterial lipopolysaccharide (LPS),i.e. in the core region of LPS from Acinetobacter baumannii NCTC 10303. The LPS was analyzed using compositional analysis, mass spectrometry, and NMR spectroscopy. The disaccharided-GlcpNβ1→6d-GlcpN, phosphorylated at O-1 and O-4′, was identified as the carbohydrate backbone of the lipid A. The Kdo tetrasaccharide is attached to O-6′ of this disaccharide and is further substituted by shortl-rhamnoglycans of varying length and by the disaccharided-GlcpNAcα1→4d-GlcpNA (GlcpNA, 2-amino-2-deoxy-glucopyranosuronic acid). The core region is not substituted by phosphate residues and represents a novel core type of bacterial LPS. The complete carbohydrate backbone of the LPS is shown in Structure I as follows: Kdo α 2 → 4 Kd 5 ↑ Glc p NAc α 1 → 4 Glc p NA α 1 → 4 Kdo α 2 5 u2003 u2003 u2002 ↑ u2003 u2003 u2002 L Rha p ∗ α 1 → 3 L Rha p ∗ α 1 → 3 L Rha p α 1 → 3 L Rha p α 1 → 8 Kdo α 2 u2003 u2003 u2002 o α 2 → 6 Glc p N β 1 → 6 Glc 4 u2002 ↑ u2002 P u2002 p N α 1 → P STRUCTUREu2002I where Rha is rhamnose. Except were indicated, monosaccharides possess thed-configuration. Sugars marked with an asterisk are present in non-stoichiometric amounts.

Core region and lipid A components of lipopolysaccharides

Publisher Summary Lipopolysaccharides (LPSs), also known as endotoxins, are one of the major virulence factors of Gram-negative bacteria. LPSs represent amphiphilic molecules generally comprising three defined regions that are distinguished by their genetics, structures, function, and biosynthesis. The first moiety, lipid A, is substituted by the second, the core region, which in turn carries a polysaccharide that may be the O-specific polysaccharide, a capsular polysaccharide, or the enterobacterial common antigen (only in Enterobacteriaceae). With regard to the structure–function relationships of LPSs, lipid A has been identified as the toxic principle of endotoxically active LPS. This toxicity depends mostly on lipid A chemical structure that defines the overall molecular conformation, but is also influenced by the core region. Thus, a complete structural analysis of lipid A and core region represent the prerequisite for the understanding of LPS functions. This chapter deals with the structural aspects of lipid A and the core region of LPSs. From the chemical point of view, the lipid A structure still remains a rather conserved architectural principle. The binding of the core region to lipid A occurs always via a Kdo residue (except in Acinetobacter). The core region is always negatively charged (provided by phosphoryl substituents and/or sugar acids like Kdo and uronic acids), which is believed to contribute to the rigidity of the Gram-negative cell wall. There are two types of core structures: those containing and those without heptoses.

Overview of the glycosylated components of the bacterial cell envelope

Publisher Summary The cell envelope represents the outermost layer of the bacterial cell that has as general functions the protection of the cell, communication with the environment, maintenance of cellular shape, stability, and rigidity of the cell, as well as allowing appropriate metabolism, growth, and division of the cell. Important components of the cell envelope are carbohydrate-based and carbohydrate-containing macromolecules that contribute significantly to all of these functions, independent of which variation of the cell envelope occurs, i.e. Gram-positive, Gram-negative, mycobacterial, or archaeal. The Gram-positive, Gram-negative, and mycobacterial cell envelopes possess a general and typical architecture, whereas the archaeal cell envelope shows a broader variety of constructions and may be comprised of only a membrane. This chapter introduces the various types of bacterial cell envelope and their carbohydrate-related molecules, as well as the glycoprotein S-layers that can be found in all bacteria except mycobacteria. It describes the structures, syntheses, and functions of carbohydrate-containing macromolecules such as lipopolysaccharides, peptidoglycan, lipoteichoic acids, teichoic acids, capsule polysaccharides, and lipoarabinomannan.

Bacterial Endotoxins: Relationships between Chemical Structure and Biological Activity of the Inner Core-Lipid a Domain

Gram-negative bacteria such as the Enterobacteriaceae and Pseudomonadaceae express at their surface various amphiphilic macromolecules among which the endotoxins are of special microbiological, immunological and medical significance. Endotoxins are essential for the organization and function of the bacterial outer membrane, and, thus, for bacterial growth and survival. As surface structures, endotoxins represent the main immunoreactive antigens (0-antigens) of gram-negative bacteria, and they are involved in the binding of antibodies and nonimmunoglobulin serum factors, and, thus, in the specific recognition and elimination of bacteria by the host organism’s defense system. Further, endotoxins are endowed with a broad spectrum of biological (endotoxic) activities, such as pyrogenicity and lethal toxicity, and they contribute to the pathogenic potential of gram-negative bacteria. Finally, endotoxins activate B-lymphocytes and mononuclear cells and are potent immunostimulators. By virtue of their biological activities they also seem to be involved in certain physiological host-parasite interactions.

Cell Wall Models

The composition and structure of cell walls are not invariable even under in vitro conditions. They do vary in dependence on cell age, composition of the cultivation medium, pH, redoxpotential, and other parameters. Under in vivo conditions such relationships are even more expressed, especially with regard to colonisation sites in the host and to the phase of progressive infection. Bacterial response to variations in the environment is partially regulated by switch-on/switch-off processes which serve the adaptation of the microorganisms to changing environmental conditions during the course of infection.