Ulrich Zähringer

Structure of de-o-acylated lipopolysaccharide from the escherichia coli re mutant strain F 515

Abstract The structure of the oligosaccharide portion of an E.coli Re lipopolysaccharide was determined as α-KDO-(2→4)-α-KDO-(2→6)-β-GlcN-α(1→6)-α-GlcN, bisphosphorylated at positions 1 and 4′. Taking into account the previous determination of the acylation pattern of the GlcN disaccharide, the total structure of E.coli Re LPS was thus established.

Primary Structure of a New Phosphocholine-containing Glycoglycerolipid of Mycoplasma fermentans

The chemical structure of a novel phosphocholine-containing glycoglycerolipid, the major polar lipid in the cell membrane of Mycoplasma fermentans PG18, was investigated by chemical analyses, gas-liquid chromatography-mass spectrometry, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, as well as one- and two-dimensional homo- and heteronuclear NMR spectroscopy and identified as 6′-O-(3-phosphocholine-2-amino-1-phospho-1,3-propanediol)-α-d-glucopyranosyl-(1′→3)-1,2-diacyl-glycerol (MfGL-II). Palmitate (16:0) and stearate (18:0), in a 3.6:1 molar ratio, constitute the major fatty acids present. MALDI-TOF mass spectrometry revealed two major pseudomolecular ions atm/z 1049.5 [MI + H]+and 1077.3 [MII + H]+ representing a dipalmitoyl as the major component and a palmitoyl-stearoyl structure as a minor component. This is the first report of 2-amino-1,3-propanediol-1,3-bisphosphate present in a natural product. This glycoglycerolipid is the second phosphocholine-containing glycoglycerolipid found in M. fermentans.

Bacterial lipopolysaccharides: relationship of structure and conformation to endotoxic activity, serological specificity and biological function.

Gram-negative bacteria express in their cell envelope various amphiphilic macromolecules among which the lipopolysaccharides (LPS) are of special significance for bacterial viability and the interaction of bacteria with host organisms. Together with phospholipids and proteins, lipopolysaccharides form the outer membrane of gram-negative bacteria. This outer membrane has an asymmetric architecture, i.e., lipopolysaccharides are located exclusively in the outer leaflet through which the bacterial cell interacts with its environment.

Molecular Aspects of the Chemistry and Biology of Endotoxin

Endotoxins are integral constituents of the outer membrane of gram-negative bacteria such as the Enterobacteriaceae, Neisseriaceae, and Chlamydiaceae (Luderitz et al. 1982). They participate in various physiological membrane functions essential for bacterial growth and survival. Endotoxins also represent the main heat-stable O-antigens of the bacteria and, thus, identify the multiplicity of serotypes. Finally, endotoxins are endowed with an overwhelming spectrum of biological activities, expressed either after injection into experimental animals, or in vitro. In fact, endotoxins have been recognized as playing an important role in the pathogenesis and manifestations of gram-negative infection, in general, and of septic shock, in particular. Thus, endotoxins are among the most potent agents capable of inducing local or generalized inflammatory reactions in both humans and experimental animals.

Structural Elucidation of Lipopolysaccharides and their Lipid a Component: Application of Soft Ionization Mass Spectrometry

Gram negative bacteria express at their surface various amphiphilic macromolecules among which the lipopolysaccharides (LPS) are of special biomedical significance. They represent the endotoxins of Gram negative bacteria eliciting in higher organisms typical pathophysiological effects such as fever, hypotension, dermal skin necrosis (local Shwartzman phenomenon) and irreversible shock and they represent the O-antigens, determining the serospecificity of LPS and of the bacteria containing them.1 Chemically, LPS consist of a polysaccharide or oligosaccharide portion covalently linked to a lipid component, termed lipid A which anchors the lipopolysaccharide in the outer leaflet of the outer cell membrane. The polysaccharide part consists of an O-specific chain which expresses high structural variability and a core oligo-saccharide which is less variable or structurally identical for many different Gram negative bacteria. The chemical structure of lipid A shows remarkable conformity for all members of the Enterobacteriaceae family and many other Gram negative bacteria. It represents the most conservative LPS region and consists of β-D-glucosaminyl-(1–6)-α-D-glucosamine disaccharide which is phosphorylated in positions 4′ of the nonreducing glucosaminyl residue (GlcN II) and in position 1 of the reducing glucosaminyl group (GlcN I). This hydrophilic backbone carries in ester and amide linkage up to seven hydroxylated and nonhydroxylated saturated fatty acid residues with chain lengths typically between ten and sixteen carbon atoms2,3. Lipid A represents the endotoxic principle of LPS being responsible for all pathophysiological effects of endotoxins. It was and still is of particular interest to find out whether the biological activity of lipid A’s of various origin can be attributed to a common chemical composition and whether a minimal endotoxically active structure can be defined. Furthermore, a correlation between the chemical structure, particularly the number and type of fatty acid residues and the degree of phosphorylation on the one hand, and the physical properties of LPS membrane systems on the other hand had been demonstrated. Thus, the thermotropic phase behavior, i. e., the various three-dimensional supramolecular phase states and the state of order adopted under physiological conditions was shown to depend on these chemical parameters.3

Bacterial Endotoxins: Relationships Between Chemical Structure and Biological Activity

Bacterial endotoxins induce in higher organisms a great number of different acute pathophysiological effects such as fever, hypotension, leukopenia followed by leukocytosis, disseminated intravascular coagulation and, in higher doses, irreversible shock (Galanos et al, 1977). In view of the obvious similarity between these biological effects and the symptoms of gram-negative bacteremia, endotoxins (released from multiplying or disintegrating bacteria), these appear to be important causative agents of certain manifestations of sepsis. Because of their pathogenic role, endotoxins have (for several decades) received worldwide scientific attention, research having been and being performed with the aim to immunologically or pharmacologically control endotoxicosis.

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.