Effect of lipopolysaccharide (LPS) chain length on interactions of bactericidal/permeability-increasing protein and its bioactive 23-kilodalton NH2-terminal fragment with isolated LPS and intact Proteus mirabilis and Escherichia coli

Abstract

The target-specific cytotoxicity for gram-negative bacteria and the endotoxin-neutralizing activity of the 55-kDa bactericidal/Permeability-increasing protein (BPI) and its bioactive 23-kDa NH2-terminal fragment depend on the strong attraction of BPI for the lipid A region of lipopolysaccharides (LPS). We have shown before that smooth gram-negative bacteria with long-chain LPS are more resistant to BPI (especially holo-BPI) than are rough strains. It has been suggested that the high BPI resistance of some gram-negative bacteria, such as Proteus mirabilis, might also reflect the structural diversity of lipid A. To explore this possibility, we compared the antibacterial activity and binding of natural and recombinant holo-BPI and a recombinant NH2-terminal fragment (rBPI-23) to an isogenic rough (Re-LPS chemotype) and a smooth (S-LPS chemotype) strain ofP. mirabilis and to LPS isolated from the two strains. Holo-BPI and rBPI-23 were both potently active against the Re strain of P. mirabilis (90%o lethal dose, 20 nM). In contrast, the smooth strain was .100 times more resistant to holo-BPI but only 10 times more resistant to rBPI-23. rBPI-23 was also more potent against several Escherichia coli strains from clinical bacteremia isolates. Differences in the antibacterial potency of BPI toward the Re and S strains of P. mirabilis correlated with differences in the binding of holo-BPI and rBPI-23 to these bacteria. In contrast, the binding of biosynthetically (in vitro transcribed and translated) 35S-labeled holo-BPI and NH2-terminal fragment to isolated Reand S-LPS from P. mirabiis in solution was similar. Moreover, in the Limulus amebocyte lysate assay, holo-BPI and rBPI-23 potently neutralized both forms of LPS with equal effectiveness. Together, these results strongly suggest that BPI recognizes Proteus lipid A and that the relative resistance of (smooth) P. mirabilis to holo-BPI is due to the inhibitory effect of long polysaccharide chains of tightly packed LPS in the envelope.

Neutrophil antimicrobial proteins enhance Shigella flexneri adhesion and invasion

“…These groups are shielded by the O‐antigen which includes many polar but uncharged glucosyl‐groups, rendering the negative charges less accessible. Indeed, BPI binding depends on the LPS O‐antigen chain length in Escherichia coli and Proteus mirabilis (Capodici et al ., 1994). It is important to note that modifications of the LPS also affect the efficiency of the TTSS (West et al ., 2005).…”

Endothelial Adhesion Molecule Expression and Its Inhibition by Recombinant Bactericidal/Permeability-Increasing Protein Are Influenced by the Capsulation and Lipooligosaccharide Structure ofNeisseria meningitidis

“…How LOS sialylation could influence rBPI 21 binding to the lipid A component of LPS is not known. Structure of polysaccharide can have an effect on the inhibitory effects of rBPI 21 on some LPSs (3). It has been demonstrated that mutants of E. coli that have incomplete LPS are much more sensitive to bactericidal permeability-increasing protein than are E. coli strains with intact LPS.…”

A murine antibacterial ortholog to human bactericidal/permeability-increasing protein (BPI) is expressed in testis, epididymis, and bone marrow

“…It is interesting that although Gram-negative bacteria display variable sensitivity to BPI, the LPS-neutralizing activity of BPI is manifest with LPS also from bacteria strains resistant to antibacterial effects of BPI. Therefore, LPS neutralization and anti-inflammatory effects of BPI may be important functions of this protein [9,10].…”