title: Structural and functional characterization of peptides derived from the carboxy-terminal region of a defensin from the tick Ornithodoros savignyi.
abstract: Tick defensins may serve as templates for the development of multifunctional peptides. The purpose of this study was to evaluate shorter peptides derived from tick defensin isoform 2 (OsDef2) in terms of their antibacterial, antioxidant, and cytotoxic activities. We compared the structural and functional properties of a synthetic peptide derived from the carboxy-terminal of the parent peptide (Os) to that of an analogue in which the three cysteine residues were omitted (Os-C). Here, we report that both peptides were bactericidal (MBC values ranging from 0.94-15 µg/ml) to both Gram-positive and Gram-negative bacteria, whereas the parent peptide only exhibited Gram-positive antibacterial activity. The Os peptide was found to be two-fold more active than Os-C against three of the four tested bacteria but equally active against Staphylococcus aureus. Os showed rapid killing kinetics against both Escherichia coli and Bacillus subtilis, whereas Os-C took longer, suggesting different modes of action. Scanning electron microscopy showed that in contrast to melittin for which blebbing of bacterial surfaces was observed, cells exposed to either peptide appeared flattened and empty. Circular dichroism data indicated that in a membrane-mimicking environment, the cysteine-containing peptide has a higher α-helical content. Both peptides were found to be non-toxic to mammalian cells. Moreover, the peptides displayed potent antioxidant activity and were 12 times more active than melittin. Multifunctional peptides hold potential for a wide range of clinical applications and further investigation into their mode of antibacterial and antioxidant properties is therefore warranted.
authors.affiliation: Department of Biochemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria 0002, South Africa.
authors.forename: Lezaan
authors.initials: L
authors.lastname: Prinsloo
authors.forename: Alex
authors.initials: A
authors.lastname: Naidoo
authors.forename: June
authors.initials: J
authors.lastname: Serem
authors.forename: Helena
authors.initials: H
authors.lastname: Taute
authors.forename: Yasien
authors.initials: Y
authors.lastname: Sayed
authors.forename: Megan
authors.initials: M
authors.lastname: Bester
authors.forename: Albert
authors.initials: A
authors.lastname: Neitz
authors.forename: Anabella
authors.initials: A
authors.lastname: Gaspar
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000737:chemistry; D001412:Bacillus subtilis / Q000187:drug effects; D002463:Cell Membrane Permeability; D002942:Circular Dichroism; D023082:Defensins / Q000008:administration & dosage* / Q000737:chemistry*; D004926:Escherichia coli / Q000187:drug effects; D006801:Humans; D026861:Ornithodoros / Q000737:chemistry; D010446:Peptide Fragments / Q000008:administration & dosage* / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013211:Staphylococcus aureus / Q000187:drug effects; D013987:Ticks / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D023082:Defensins; D010446:Peptide Fragments