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Fig. 3. Schematic structure of various mutant LPS from S. minnesota. The length of the oligosaccharide part decreases in the chemotype sequence Ra, Rb, Rc, Rd, and Re, the corresponding strains from S. minnesota are R60, R345, R5, R4, and R595. primary chemical structure and is influenced by ambient conditions like temperature, pH, water content, and concentration of mono- and divalent cations. The molecular shape of a given amphiphilic molecule like LPS or lipid A within a supramolecular aggregate is not a constant but will depend, at least in part, on the fluidity (inversely correlated to the state of order) of its acyl chains which can assume two main phase states, the well known gel (B) phase and liquid-crystalline (a) phase. At a characteristic phase transition temperature T., a reversible transition between these two phases takes place. JT, depends on the length and the degree of saturation of the acyl chains as well as on the conformation and the charge density of and their Endotoxins (LPS and lipid A) as amphiphilic mole- cules form aggregates in aqueous environments above a critical concentration (critical micellar concentration, CMC), depending among other things on their hydro- phobicity.*° The actual structure of these aggregates depends on the conformation (shape) of the contribut- ing molecules, which is again determined by their

Figure 3 Schematic structure of various mutant LPS from S. minnesota. The length of the oligosaccharide part decreases in the chemotype sequence Ra, Rb, Rc, Rd, and Re, the corresponding strains from S. minnesota are R60, R345, R5, R4, and R595. primary chemical structure and is influenced by ambient conditions like temperature, pH, water content, and concentration of mono- and divalent cations. The molecular shape of a given amphiphilic molecule like LPS or lipid A within a supramolecular aggregate is not a constant but will depend, at least in part, on the fluidity (inversely correlated to the state of order) of its acyl chains which can assume two main phase states, the well known gel (B) phase and liquid-crystalline (a) phase. At a characteristic phase transition temperature T., a reversible transition between these two phases takes place. JT, depends on the length and the degree of saturation of the acyl chains as well as on the conformation and the charge density of and their Endotoxins (LPS and lipid A) as amphiphilic mole- cules form aggregates in aqueous environments above a critical concentration (critical micellar concentration, CMC), depending among other things on their hydro- phobicity.*° The actual structure of these aggregates depends on the conformation (shape) of the contribut- ing molecules, which is again determined by their

Related Figures (9)

1. Introduction Keywords: Glycoconjugates; Bacterial polysaccharides; Lipopolysaccharides; Endotoxins; Cytokines
1. Introduction Keywords: Glycoconjugates; Bacterial polysaccharides; Lipopolysaccharides; Endotoxins; Cytokines
Fig. 1. Repeating unit of a cell-wall antigenic polysaccharide from the Gram-positive species E. saburreum (adapted from Sato and coworkers!*). Xul = L-threo-pent-2-ulose; Fuc = D- fucose; Hep = p-glycero-p-galacto-heptose. The combination of a variety of techniques allows the determination of the complete structure of a polysac- charide. Thus, for example, Sato and coworkers!'® established a novel structure of a bacterial cell-wall polysaccharide from a Gram-positive bacterium. The structure of the antigenic polysaccharide produced by Eubacterium saburreum T15 was determined using acid
Fig. 1. Repeating unit of a cell-wall antigenic polysaccharide from the Gram-positive species E. saburreum (adapted from Sato and coworkers!*). Xul = L-threo-pent-2-ulose; Fuc = D- fucose; Hep = p-glycero-p-galacto-heptose. The combination of a variety of techniques allows the determination of the complete structure of a polysac- charide. Thus, for example, Sato and coworkers!'® established a novel structure of a bacterial cell-wall polysaccharide from a Gram-positive bacterium. The structure of the antigenic polysaccharide produced by Eubacterium saburreum T15 was determined using acid
Fig. 2. Schematic representation of the activation mechanisms induced by LPS. LPS is released from the bacterial outer membrane by the attack of immune components (drugs, proteins) or simply by cell division. It may interact with serum and membrane proteins, which subsequently leads to an activation of macrophages, which secret mediators such as tumor-necrosis-factor-% and interleukins.
Fig. 2. Schematic representation of the activation mechanisms induced by LPS. LPS is released from the bacterial outer membrane by the attack of immune components (drugs, proteins) or simply by cell division. It may interact with serum and membrane proteins, which subsequently leads to an activation of macrophages, which secret mediators such as tumor-necrosis-factor-% and interleukins.
Fig. 4. Chemical structures of various LPS Re and lipid A part structures.
Fig. 4. Chemical structures of various LPS Re and lipid A part structures.
Fig. 5. Interleukin-6 inducing activity and the order parameter S (37 °C) of the acyl chains at 37 °C of various LPS Re and lipid A part structures. In the top figure, low values indicate high biological activity; in the bottom figure, low values indicate high mobility of the acyl chains. 2.2.3. General ultrastructural studies. Electron micro- scopy has become an essential tool in the identification and characterization of the morphological properties of endotoxins. In older papers on the aggregate structures of LPS*!? the impurity of the samples did not allow a reliable description, since contaminants such as proteins led to artefacts in the aggregate structure. Amano and coworkers**? have used electron microscopy for the elucidation of structures of lipopolysaccharides from cations as well as a lowering of pH caused a significan rigidification of the acyl chains of free lipid A and LPS preparations and, partly, also led to an increase in T,. A basic pH, a lowering of T, was observed. Concomitant with a decrease of T,, a fluidization of the LPS and lipid A acyl chains occurred.** Excess concentrations o Mg’ led to an increase of T, for LPS from S. minnesota and to LPS from Erwinia carotovora a [endotoxin]:[cation] = 1:1 M (Mg?* or Ca**).??*° The comparison of the influence of divalent cations on the phase behaviour of LPS Re showed a cation-specific increase of T, in the sequence Mg** <Ni** <Co** <
Fig. 5. Interleukin-6 inducing activity and the order parameter S (37 °C) of the acyl chains at 37 °C of various LPS Re and lipid A part structures. In the top figure, low values indicate high biological activity; in the bottom figure, low values indicate high mobility of the acyl chains. 2.2.3. General ultrastructural studies. Electron micro- scopy has become an essential tool in the identification and characterization of the morphological properties of endotoxins. In older papers on the aggregate structures of LPS*!? the impurity of the samples did not allow a reliable description, since contaminants such as proteins led to artefacts in the aggregate structure. Amano and coworkers**? have used electron microscopy for the elucidation of structures of lipopolysaccharides from cations as well as a lowering of pH caused a significan rigidification of the acyl chains of free lipid A and LPS preparations and, partly, also led to an increase in T,. A basic pH, a lowering of T, was observed. Concomitant with a decrease of T,, a fluidization of the LPS and lipid A acyl chains occurred.** Excess concentrations o Mg’ led to an increase of T, for LPS from S. minnesota and to LPS from Erwinia carotovora a [endotoxin]:[cation] = 1:1 M (Mg?* or Ca**).??*° The comparison of the influence of divalent cations on the phase behaviour of LPS Re showed a cation-specific increase of T, in the sequence Mg** <Ni** <Co** <
With: MW=molecular weight, A. =second viral coeffi- cient, R, = gyration radius, R, = hydrodynamic radius. The given error boundaries are the standard deviations (adapted from Santos and coworkers 2003)°* Physical parameters obtained by light scattering of LPS (E. coli, serotype 026:B6) above and below the CMC (transition into a less aggregated form, CMC, = 14 pg/mL, see text) in PBS (pH 7.4) at 37°C
With: MW=molecular weight, A. =second viral coeffi- cient, R, = gyration radius, R, = hydrodynamic radius. The given error boundaries are the standard deviations (adapted from Santos and coworkers 2003)°* Physical parameters obtained by light scattering of LPS (E. coli, serotype 026:B6) above and below the CMC (transition into a less aggregated form, CMC, = 14 pg/mL, see text) in PBS (pH 7.4) at 37°C
Fig. 7. Chemical structures, X-ray diffraction patterns, molecular conformation, and biological activity of various lipid A and part structures. Amphiphiles with shape parameters in the range }< S <1 assume lamellar (L) structures, and those with a prominent axis of the head-group and S>1 adopt inverted hexagonal (Hj;) structures. In the latter case, the water component is assumed to form idealized circular rods lined with the hydrated lipid backbones and with the remaining volume filled by the fluid hydrocarbon chains. Another category are the cubic (Q) structures, which have three-dimensional geometry and cannot be described by a unique structure™ other
Fig. 7. Chemical structures, X-ray diffraction patterns, molecular conformation, and biological activity of various lipid A and part structures. Amphiphiles with shape parameters in the range }< S <1 assume lamellar (L) structures, and those with a prominent axis of the head-group and S>1 adopt inverted hexagonal (Hj;) structures. In the latter case, the water component is assumed to form idealized circular rods lined with the hydrated lipid backbones and with the remaining volume filled by the fluid hydrocarbon chains. Another category are the cubic (Q) structures, which have three-dimensional geometry and cannot be described by a unique structure™ other
Fig. 6. Synchrotron radiation X-ray diffraction patterns of lipid A from S. minnesota deep rough mutant LPS Re in dependence on temperature at 85% water content and [lipid A]: [Mg**]=1:1 molar. The patterns indicate a triphasic beha- viour with a multilamellar (L) structure at lower, a cubic (Q) structure at medium, and an inverted hexagonal (H);) structure at the highest temperatures.
Fig. 6. Synchrotron radiation X-ray diffraction patterns of lipid A from S. minnesota deep rough mutant LPS Re in dependence on temperature at 85% water content and [lipid A]: [Mg**]=1:1 molar. The patterns indicate a triphasic beha- viour with a multilamellar (L) structure at lower, a cubic (Q) structure at medium, and an inverted hexagonal (H);) structure at the highest temperatures.
Aggregate structure, order parameter S (37°C), phase transition temperature 7,, and the relative biological activity for lipid A structures from different origin (according to Ref. 72 and unpublished results)
Aggregate structure, order parameter S (37°C), phase transition temperature 7,, and the relative biological activity for lipid A structures from different origin (according to Ref. 72 and unpublished results)
Related topics:
Organic ChemistryMolecular ConformationCritical micellar concentrationBiochemistry and cell biology
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