title: Structure--activity study of the antibacterial peptide fallaxin.
abstract: Fallaxin is a 25-mer antibacterial peptide amide, which was recently isolated from the West Indian mountain chicken frog Leptodactylus fallax. Fallaxin has been shown to inhibit the growth of several Gram-negative bacteria including Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Here, we report a structure-activity study of fallaxin based on 65 analogs, including a complete alanine scan and a full set of N- and C-terminal truncated analogs. The fallaxin analogs were tested for hemolytic activity and antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-intermediate resistant S. aureus, (VISA), methicillin-susceptible S. aureus (MSSA), E. coli, K. pneumoniae, and P. aeruginosa. We identified several analogs, which showed improved antibacterial activity compared to fallaxin. Our best candidate was FA12, which displayed MIC values of 3.12, 25, 25, and 50 muM against E. coli, K. pneumoniae, MSSA, and VISA, respectively. Furthermore, we correlated the antibacterial activity with various structural parameters such as charge, hydrophobicity H, mean hydrophobic moment mu(H), and alpha-helicity. We were able to group the active and inactive analogs according to mean hydrophobicity H and mean hydrophobic moment mu(H). Far-UV CD-spectroscopy experiments on fallaxin and several analogs in buffer, in TFE, and in membrane mimetic environments (small unilamellar vesicles) indicated that a coiled-coil conformation could be an important structural trait for antibacterial activity. This study provides data that support fallaxin analogs as promising lead structures in the development of new antibacterial agents.
authors.affiliation: Department of Natural Sciences, Faculty of Life Sciences, University of Copenhagen, 1871 Copenhagen, Denmark.
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Nielsen
authors.forename: Niels
authors.initials: N
authors.lastname: Frimodt-Møller
authors.forename: Birthe B
authors.initials: BB
authors.lastname: Kragelund
authors.forename: Paul R
authors.initials: PR
authors.lastname: Hansen
mesh_terms: D000596:Amino Acids / Q000032:analysis; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D002021:Buffers; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D024881:Drug Resistance, Bacterial / Q000187:drug effects*; D004912:Erythrocytes / Q000187:drug effects*; D006090:Gram-Negative Bacteria / Q000187:drug effects; D006094:Gram-Positive Bacteria / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D008712:Methicillin / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D014640:Vancomycin / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D023181:Antimicrobial Cationic Peptides; D002021:Buffers; C524839:fallaxin, Leptodactylus fallax; D014640:Vancomycin; D008712:Methicillin