title: Maculatin 1.1 disrupts Staphylococcus aureus lipid membranes via a pore mechanism.
abstract: Maculatin 1.1 (Mac1) showed potent activity against Staphylococcus aureus with an MIC of 7 μM. The mode of action of Mac1 was investigated by combining assays with S. aureus cells and lipid vesicles mimicking their membrane composition. A change in Mac1 conformation was monitored by circular dichroism from random coil to ca. 70% α-helix structure in contact with vesicles. Electron micrographs of S. aureus incubated with Mac1 showed rough and rippled cell surfaces. An uptake of 65% of small (FD, 4 kDa [FD-4]) and 35% of large (RD, 40 kDa [RD-40]) fluorescent dextrans by S. aureus was observed by flow cytometry and indicate that Mac1 formed a pore of finite size. In model membranes with both dyes encapsulated together, the full release of FD-4 occurred, but only 40% of RD-40 was reached, supporting the flow cytometry results, and indicating a pore size between 1.4 and 4.5 nm. Finally, solid-state nuclear magnetic resonance showed formation of an isotropic phase signifying highly mobile lipids such as encountered in a toroidal pore structure. Overall, Mac1 is a promising antimicrobial peptide with the potent capacity to form pores in S. aureus membranes.
authors.affiliation: School of Chemistry, Bio21 Institute, The University of Melbourne, Melbourne, Victoria, Australia. msani@unimelb.edu.au
authors.forename: M-A
authors.initials: MA
authors.lastname: Sani
authors.forename: T C
authors.initials: TC
authors.lastname: Whitwell
authors.forename: J D
authors.initials: JD
authors.lastname: Gehman
authors.forename: R M
authors.initials: RM
authors.lastname: Robins-Browne
authors.forename: N
authors.initials: N
authors.lastname: Pantarat
authors.forename: T J
authors.initials: TJ
authors.lastname: Attard
authors.forename: E C
authors.initials: EC
authors.lastname: Reynolds
authors.forename: N M
authors.initials: NM
authors.lastname: O'Brien-Simpson
authors.forename: F
authors.initials: F
authors.lastname: Separovic
mesh_terms: D029845:Amphibian Proteins / Q000138:chemical synthesis / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000138:chemical synthesis / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides / Q000138:chemical synthesis / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D002463:Cell Membrane Permeability; D002942:Circular Dichroism; D003911:Dextrans / Q000494:pharmacology; D004353:Drug Evaluation, Preclinical; D005453:Fluorescence; D008051:Lipid Bilayers / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D008970:Molecular Weight; D016062:Porosity; D017433:Protein Structure, Secondary; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D029845:Amphibian Proteins; D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D003911:Dextrans; D008051:Lipid Bilayers; C113499:maculatin-1.1 protein, Litoria