Morphology, size distribution, and aggregate structure of lipopolysaccharide and lipid A dispersions from enterobacterial origin

Abstract

Lipopolysaccharides (LPSs) from Gram-negative bacteria are strong elicitors of the human immune systems. There is strong evidence that aggregates and not monomers of LPS play a decisive role at least in the initial stages of cell activation of immune cells such as mononuclear cells. In previous reports, it was shown that the biologically most active part of enterobacterial LPS, hexa-acyl bisphosphorylated lipid A, adopts a particular supramolecular conformation, a cubic aggregate structure. However, little is known about the size and morphology of these aggregates, regarding the fact that LPS may have strong variations in the length of the saccharide chains (various rough mutant and smooth-form LPS). Thus, in the present paper, several techniques for the determination of details of the aggregate morphology such as freeze-fracture and cryo-electron microscopy, analytical ultracentrifugation, laser backscattering analysis, and small-angle X-ray scattering were applied for various endotoxin (lipid A and different LPS) preparations. The data show a variety of different morphologies not only for different endotoxins but also when comparing different applied techniques. The data are interpreted with respect to the suitability of the single techniques, in particular on the basis of available literature data.

NMR-based Structural Analysis of the Complete Rough-type Lipopolysaccharide Isolated from Capnocytophaga canimorsus

“…However, conformational studies of the LPS molecule expressing relevant biological (i.e. endotoxic active) conformations in an aqueous solvent system cannot be achieved by this approach (16).…”

Supramolecular structure of enterobacterial wild-type lipopolysaccharides (LPS), fractions thereof, and their neutralization by Pep19-2.5

“…In none of these investigations, however, techniques like SAXS ans SANS were performed which allowed beyond the morphology the determination of the three-dimensional aggregate structure. An overview of these findings is given by Richter et al (32).…”

LptE binds to and alters the physical state of LPS to catalyze its assembly at the cell surface

“…The combination of structural and genetic evidence led us to hypothesize that LptE interacts with LPS at R91 and K136 as a requirement for translocation to the cell surface. Solubilized LPS has the propensity to form aggregates making biochemical characterization challenging (32). Therefore, we performed binding experiments on LPS-coated surfaces.…”