Human CAP18: a novel antimicrobial lipopolysaccharide-binding protein

Abstract

CAP18 (18-kDa cationic antimicrobial protein) is a protein originally identified and purified from rabbit leukocytes on the basis of its capacity to bind and inhibit various activities of lipopolysaccharide (LPS). Here we report the cloning of human CAP18 and characterize the anti-LPS activity of the C-terminal fragment. Oligonucleotide probes designed from the rabbit CAP18 cDNA were used to identify human CAP18 from a bone marrow cDNA library. The cDNA encodes a protein composed of a 30-amino-acid signal peptide, a 103-aminoacid N-terminal domain of unknown function, and a C-terminal domain of 37 amino acids homologous to the LPS-binding antimicrobial domain of rabbit CAP18, designated CAP18 104-140. A human CAP18-specific antiserum was generated by using CAP18 expressed as a fusion protein with the maltose-binding protein. Western blots (immunoblots) with this antiserum showed specific expression of human CAP18 in granulocytes. Synthetic human CAP18 104-140 and a more active truncated fragment, CAP18 104-135 , were shown to (i) bind to erythrocytes coated with diverse strains of LPS, (ii) inhibit LPS-induced release of nitric oxide from macrophages, (iii) inhibit LPS-induced generation of tissue factor, and (iv) protect mice from LPS lethality. CAP18 104-140 may have therapeutic utility for conditions associated with elevated concentrations of LPS.

Antimicrobial peptides and endotoxin inhibit cytokine and nitric oxide release but amplify respiratory burst response in human and murine macrophages

“…Cationic AMP neutralize endotoxin's TLR4-dependent induction of cellular cytokine and nitric oxide release. This is accomplished either by binding directly to endotoxin or by blocking the binding of endotoxin to LBP thus attenuating or neutralizing endotoxin's inflammatory effects (Larrick et al, 1995;Scott et al, 2000;Nagaoka et al, 2001). Physico-chemical analysis of endotoxin indicates that lipid A conformation and supramolecular aggregate structure determine TLR4-dependent biological activity, i.e.…”

Interpretation of biological activity data of bacterial endotoxins by simple molecular models of mechanism of action

“…Beamer et al [46] concluded from LPS-binding studies of bactericidal permeabilityincreasing protein that two b-hairpin structures around residues 45 and 96 in the N-terminal domain KIKHLGK and KRFLK dominated by basic residues have been implicated in LPS binding. The C-terminal domain of human CAP18 contained a group of basic residues in the sequence KRIVQR (residues 123±128) and was observed to bind LPS [49,51]. Rustici et al [52] synthesized small peptide analogues of polymyxin B, a peptide-like antibiotic that binds LPS.…”

The relation of innate and adaptive immunity with viral-induced acute asthma attacks: Focusing on IP-10 and cathelicidin

“…36 The modulation of TLR function by cathelicidin can be considered an anti-inflammatory effect. 5 Cathelicidin downregulates signaling through TLR4, 37 whereas it stabilizes TLR3 ligands and enhances viral responses transmitted via this receptor in bronchial epithelial cells. 38 Although the cathelicidin molecule has a general anti-inflammatory effect on TLR stimulation by inhibiting the pro-inflammatory cytokine release from monocytic cells stimulated with TLR2 and TLR4, it can enhance or abrogate inflammatory signals depending on cell type and the microenvironment.…”