title: Activities of LL-37, a cathelin-associated antimicrobial peptide of human neutrophils.
abstract: Human neutrophils contain two structurally distinct types of antimicrobial peptides, beta-sheet defensins (HNP-1 to HNP-4) and the alpha-helical peptide LL-37. We used radial diffusion assays and an improved National Committee for Clinical Laboratory Standards-type broth microdilution assay to compare the antimicrobial properties of LL-37, HNP-1, and protegrin (PG-1). Although generally less potent than PG-1, LL-37 showed considerable activity (MIC, <10 microgram/ml) against Pseudomonas aeruginosa, Salmonella typhimurium, Escherichia coli, Listeria monocytogenes, Staphylococcus epidermidis, Staphylococcus aureus, and vancomycin-resistant enterococci, even in media that contained 100 mM NaCl. Certain organisms (methicillin-resistant S. aureus, Proteus mirabilis, and Candida albicans) were resistant to LL-37 in media that contained 100 mM NaCl but were susceptible in low-salt media. Burkholderia cepacia was resistant to LL-37, PG-1, and HNP-1 in low- or high-salt media. LL-37 caused outer and inner membrane permeabilization of E. coli ML-35p. Chromogenic Limulus assays revealed that LL-37 bound to E. coli O111:B4 lipopolysaccharide (LPS) with a high affinity and that this binding showed positive cooperativity (Hill coefficient = 2.02). Circular dichroism spectrometry disclosed that LL-37 underwent conformational change in the presence of lipid A, transitioning from a random coil to an alpha-helical structure. The broad-spectrum antimicrobial properties of LL-37, its presence in neutrophils, and its inducibility in keratinocytes all suggest that this peptide and its precursor (hCAP-18) may protect skin and other tissues from bacterial intrusions and LPS-induced toxicity. The potent activity of LL-37 against P. aeruginosa, including mucoid and antibiotic-resistant strains, suggests that it or related molecules might have utility as topical bronchopulmonary microbicides in cystic fibrosis.
authors.affiliation: Department of Medicine, Center for the Health Sciences, Los Angeles, California, USA.
authors.forename: J
authors.initials: J
authors.lastname: Turner
authors.forename: Y
authors.initials: Y
authors.lastname: Cho
authors.forename: N N
authors.initials: NN
authors.lastname: Dinh
authors.forename: A J
authors.initials: AJ
authors.lastname: Waring
authors.forename: R I
authors.initials: RI
authors.lastname: Lehrer
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000890:Anti-Infective Agents / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins / Q000494:pharmacology*; D054804:Cathelicidins; D002463:Cell Membrane Permeability; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011506:Proteins / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D023181:Antimicrobial Cationic Peptides; D002352:Carrier Proteins; D054804:Cathelicidins; D008070:Lipopolysaccharides; D011506:Proteins; C084515:cathelin; D002118:Calcium