title: Inhibition of cathelicidin activity by bacterial exopolysaccharides.
abstract: The interaction of bacterial exopolysaccharides, produced by opportunistic lung pathogens, with antimicrobial peptides of the innate primate immune system was investigated. The exopolysaccharides were produced by Pseudomonas aeruginosa, Inquilinus limosus and clinical isolates of the Burkholderia cepacia complex, bacteria that are all involved in lung infections of cystic fibrosis patients. The effects of the biological activities of three orthologous cathelicidins from Homo sapiens sapiens, Pongo pygmaeus (orangutan) and Presbitys obscurus (dusky leaf monkey) were examined. Inhibition of the antimicrobial activity of peptides was assessed using minimum inhibitory concentration assays on a reference Escherichia coli strain in the presence and absence of exopolysaccharides, whereas complex formation between peptides and exopolysaccharides was investigated by means of circular dichroism, fluorescence spectroscopy and atomic force microscopy. Biological assays revealed that the higher the negative charge of exopolysaccharides the stronger was their inhibiting effect. Spectroscopic studies indicated the formation of molecular complexes of varying stability between peptides and exopolysaccharides, explaining the inhibition. Atomic force microscopy provided a direct visualization of the molecular complexes. A model is proposed where peptides with an alpha-helical conformation interact with exopolysaccharides through electrostatic and other non-covalent interactions.
authors.affiliation: Department of Life Sciences, University of Trieste, Trieste, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Foschiatti
authors.forename: Paola
authors.initials: P
authors.lastname: Cescutti
authors.forename: Alessandro
authors.initials: A
authors.lastname: Tossi
authors.forename: Roberto
authors.initials: R
authors.lastname: Rizzo
mesh_terms: D000818:Animals; D042602:Burkholderia cepacia complex / Q000737:chemistry; D054804:Cathelicidins / Q000037:antagonists & inhibitors*; D002942:Circular Dichroism; D003550:Cystic Fibrosis / Q000382:microbiology; D004926:Escherichia coli / Q000187:drug effects; D000882:Haplorhini; D006801:Humans; D008826:Microbial Sensitivity Tests; D018625:Microscopy, Atomic Force; D008968:Molecular Conformation; D011135:Polysaccharides, Bacterial / Q000494:pharmacology*; D011148:Pongo pygmaeus; D011550:Pseudomonas aeruginosa / Q000737:chemistry; D012244:Rhodospirillaceae / Q000737:chemistry; D013050:Spectrometry, Fluorescence
chemical_list: D054804:Cathelicidins; D011135:Polysaccharides, Bacterial