Structural basis for endotoxic and antagonistic activities: investigation with novel synthetic lipid A analogs

Abstract

Our early work using homogeneous synthetic preparations demonstrated the presence of a lipid A analog which antagonizes endotoxic activities of LPS and lipid A. The first example was a tetraacylated biosynthetic precursor, now known as precursor Ia or lipid IVa, that contains four 3-hydroxytetradecanoyl moieties linked to the bisphosphorylated disaccharide backbone common to the endotoxic hexa-acyl Escherichia coli lipid A. Various compounds with both endotoxic and antagonistic activities have subsequently been reported from either natural or synthetic sources, but little is known about the factors determining the type of the activities of the respective compounds. To approach this issue, we have synthesized a series of lipid A analogs with various numbers and chain lengths of acyl groups on the backbone. Some were prepared by the aid of a novel affinity separation procedure. The phosphate moieties were also synthetically replaced. Biological tests showed that at least three acyl groups are required for antagonistic activity but one or even both of the phosphates can be replaced with other acidic moieties without losing the activity. The effect of Kdo residues linked to lipid A is also briefly discussed. Molecular dynamics calculations reasonably explain possible conformations required for the biological activity.

Structural prerequisites for endotoxic activity in the Limulus test as compared to cytokine production in mononuclear cells

“…The used synthetic hexa-acyl lipid A compounds 506, CM-506, and tetra-acyl lipid A 406, carboxymethylated Bis-CM-506 and Bis-CM-406 as well as monophosphoryl compounds 504 (4 0 -phosphate) and 505 (1-phosphate) and Kdo-505 and Kdo-506 have been described previously. [16][17][18][19][20][21] The chemical structures of various lipid A analogues are presented in Figure 1.…”

The Structural Basis for Lipid and Endotoxin Binding in RP105-MD-1, and Consequences for Regulation of Host Lipopolysaccharide Sensitivity

“…Hexa-acylated LPA from Escherichia coli is a TLR4 agonist, and is endotoxic to human macrophage and mouse cells depending upon its structure (Muroi et al, 2002;Bryant et al, 2010;Needham and Trent, 2013). The tetra-acylated precursor lipid IVa (LPIVa) (Kusumoto et al, 2003) (Figure 2A) acts as an antagonist in human cells but as an agonist in mouse cells (Golenbock et al, 1991;Means et al, 2000). The immunomodulatory properties of different lipid A analogs makes them of great biomedical interest (O'Neill et al, 2009), but their low solubility (Galloway and Raetz, 1990;Gutsmann et al, 2007) and complex phase behavior (Brandenburg and Seydel, 2009;Gutsmann et al, 2007) complicates structural and biophysical studies.…”

Mechanism regulating cell surface expression and activation of Toll‐like receptor 4

“…A number of studies on the activity of lipid A indicate that hexacylated lipid A from Escherichia coli with side chains of 12–14 carbons in length maximally stimulates TLR4 29. Altering the number or length of the attached fatty acids or altering the charge of lipid A can reduce the magnitude of activation 30–32. Different types of lipid A can induce different magnitudes of activation.…”