title: Antimicrobial action and cell agglutination by the eosinophil cationic protein are modulated by the cell wall lipopolysaccharide structure.
abstract: Antimicrobial proteins and peptides (AMPs) are essential effectors of innate immunity, acting as a first line of defense against bacterial infections. Many AMPs exhibit high affinity for cell wall structures such as lipopolysaccharide (LPS), a potent endotoxin able to induce sepsis. Hence, understanding how AMPs can interact with and neutralize LPS endotoxin is of special relevance for human health. Eosinophil cationic protein (ECP) is an eosinophil secreted protein with high activity against both Gram-negative and Gram-positive bacteria. ECP has a remarkable affinity for LPS and a distinctive agglutinating activity. By using a battery of LPS-truncated E. coli mutant strains, we demonstrate that the polysaccharide moiety of LPS is essential for ECP-mediated bacterial agglutination, thereby modulating its antimicrobial action. The mechanism of action of ECP at the bacterial surface is drastically affected by the LPS structure and in particular by its polysaccharide moiety. We have also analyzed an N-terminal fragment that retains the whole protein activity and displays similar cell agglutination behavior. Conversely, a fragment with further minimization of the antimicrobial domain, though retaining the antimicrobial capacity, significantly loses its agglutinating activity, exhibiting a different mechanism of action which is not dependent on the LPS composition. The results highlight the correlation between the protein's antimicrobial activity and its ability to interact with the LPS outer layer and promote bacterial agglutination.
authors.affiliation: Department of Biochemistry and Molecular Biology, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Pulido
authors.forename: Mohammed
authors.initials: M
authors.lastname: Moussaoui
authors.forename: David
authors.initials: D
authors.lastname: Andreu
authors.forename: M Victòria
authors.initials: MV
authors.lastname: Nogués
authors.forename: Marc
authors.initials: M
authors.lastname: Torrent
authors.forename: Ester
authors.initials: E
authors.lastname: Boix
mesh_terms: D000371:Agglutination / Q000187:drug effects; D001422:Bacterial Adhesion / Q000187:drug effects; D001665:Binding Sites; D002236:Carbohydrate Conformation; D002473:Cell Wall / Q000737:chemistry*; D047150:Eosinophil Cationic Protein / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D004804:Eosinophils / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D006801:Humans; D008070:Lipopolysaccharides / Q000737:chemistry* / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D013329:Structure-Activity Relationship
chemical_list: D008070:Lipopolysaccharides; D009842:Oligopeptides; D011994:Recombinant Proteins; D047150:Eosinophil Cationic Protein