The role of polar and facial amphipathic character in determining lipopolysaccharide-binding properties in synthetic cationic peptides

Two series of peptides, designated K and NK were synthesized and tested for lipid A binding and neutralizing properties. K-2, which has an 11-residue amphiphilic core, and a branched N-terminus bearing two branched lysinyl re sidues does not bind lipid A, while NK2, also with an 11-residue amphiphili c core comprised entirely of non-ionizable residues, and a similarly branch ed, cationic N-terminus, binds lipid A very weakly. Both peptides do not in hibit lipopolysaccharide (LPS) activity in the Limulus assay, nor do they i nhibit LPS-induced TNF-alpha and NO production in 5774 cells. These results are entirely unlike a homologous peptide with an exclusively hydrophobic c ore whose LPS-binding and neutralizing properties are very similar to that of polymyxin B [David SA, Awasthi SK, Wiese A et al. Characterization of th e interactions of a polycationic, amphiphilic, terminally branched oligopep tide with lipid A and lipopolysaccharide from the deep rough mutant of Salm onella minnesota. J Endotoxin Res 1996; 3: 369-379]. These data suggest tha t a clear segregation of charged and apolar domains is crucial in molecules designed for purposes of LPS sequestration and that head-tail (polar) orie ntation of the cationic/hydrophobic regions is preferable to molecules with mixed or facial cationic/amphipathic character.