title: The central kink region of fowlicidin-2, an alpha-helical host defense peptide, is critically involved in bacterial killing and endotoxin neutralization.
abstract: Fowlicidins are a group of newly identified chicken cathelicidin host defense peptides. We have shown that the putatively mature fowlicidin-2 of 31 amino acid residues possesses potent antibacterial and lipopolysaccharide (LPS)- neutralizing activities, but with a noticeable toxicity to mammalian cells. As a first step in exploring the structure-activity relationships of fowlicidin-2, in this study we determined its tertiary structure by nuclear magnetic resonance spectroscopy. Unlike the majority of cathelicidins, which are composed of a predominant alpha-helix with a short hinge sequence near the center, fowlicidin-2 consists of 2 well-defined alpha-helical segments (residues 6-12 and 23-27) connected by a long extensive kink (residues 13-20) induced by proline. To further investigate the functional significance of each of these structural components, several N- and C-terminal deletion analogs of fowlicidin-2 were synthesized and analyzed for their antibacterial, cytotoxic and LPS-neutralizing activities. Our results indicated that neither the N- nor C-terminal alpha-helix alone is sufficient to confer any function. Rather, fowlicidin-2(1-18) and fowlicidin-2(15-31), 2 alpha-helical segments with inclusion of the central cationic kink region, retained substantial capacities to kill bacteria and neutralize the LPS-induced proinflammatory response, relative to the parent peptide. More desirably, these 2 peptide analogs showed substantially reduced toxicity to human erythrocytes and epithelial cells, indicative of improved potential as antibacterial and antisepsis agents. To our knowledge, fowlicidin-2 is the first alpha-helical cathelicidin, with the central kink region shown to be critically important in killing bacteria and neutralizing LPS.
authors.affiliation: Department of Animal Science, Oklahoma State University, Stillwater, Okla. 74078, USA.
authors.forename: Yanjing
authors.initials: Y
authors.lastname: Xiao
authors.forename: Alvaro I
authors.initials: AI
authors.lastname: Herrera
authors.forename: Yugendar R
authors.initials: YR
authors.lastname: Bommineni
authors.forename: Jose L
authors.initials: JL
authors.lastname: Soulages
authors.forename: Om
authors.initials: O
authors.lastname: Prakash
authors.forename: Guolong
authors.initials: G
authors.lastname: Zhang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology / Q000633:toxicity; D018938:Caco-2 Cells; D002942:Circular Dichroism; D004731:Endotoxins / Q000276:immunology*; D004912:Erythrocytes / Q000502:physiology; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D006461:Hemolysis; D006801:Humans; D007113:Immunity, Innate; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D013329:Structure-Activity Relationship
chemical_list: D023181:Antimicrobial Cationic Peptides; C504855:CMAP27 protein, chicken; D004731:Endotoxins