title: Divorcing folding from function: how acylation affects the membrane-perturbing properties of an antimicrobial peptide.
abstract: Many small cationic peptides, which are unstructured in aqueous solution, have antimicrobial properties. These properties are assumed to be linked to their ability to permeabilize bacterial membranes, accompanied by the transition to an alpha-helical folding state. Here we show that there is no direct link between folding of the antimicrobial peptide Novicidin (Nc) and its membrane permeabilization. N-terminal acylation with C8-C16 alkyl chains and the inclusion of anionic lipids both increase Nc's ability to form alpha-helical structure in the presence of vesicles. Nevertheless, both acylation and anionic lipids reduce the extent of permeabilization of these vesicles and lead to slower permeabilization kinetics. Furthermore, acylation significantly decreases antimicrobial activity. Although acyl chains of increasing length also increase the tendency of the peptides to aggregate in solution, this cannot rationalize our results since permeabilization and antimicrobial activities are observed well below concentrations where aggregation occurs. This suggests that significant induction of alpha-helical structure is not a prerequisite for membrane perturbation in this class of antimicrobial peptides. Our data suggests that for Nc, induction of alpha-helical structure may inhibit rather than facilitate membrane disruption, and that a more peripheral interaction may be the most efficient permeabilization mechanism. Furthermore, acylation leads to a deeper embedding in the membrane, which could lead to an anti-permeabilizing "plugging" effect.
authors.affiliation: Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Molecular Biology, Gustav Wieds Vej 10C, University of Aarhus, DK - 8000 Aarhus C, Denmark.
authors.forename: Brian
authors.initials: B
authors.lastname: Vad
authors.forename: Line Aagot
authors.initials: LA
authors.lastname: Thomsen
authors.forename: Kresten
authors.initials: K
authors.lastname: Bertelsen
authors.forename: Magnus
authors.initials: M
authors.lastname: Franzmann
authors.forename: Jan Mondrup
authors.initials: JM
authors.lastname: Pedersen
authors.forename: Søren B
authors.initials: SB
authors.lastname: Nielsen
authors.forename: Thomas
authors.initials: T
authors.lastname: Vosegaard
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Valnickova
authors.forename: Troels
authors.initials: T
authors.lastname: Skrydstrup
authors.forename: Jan J
authors.initials: JJ
authors.lastname: Enghild
authors.forename: Reinhard
authors.initials: R
authors.lastname: Wimmer
authors.forename: Niels Chr
authors.initials: NC
authors.lastname: Nielsen
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Otzen
mesh_terms: D000215:Acylation; D000595:Amino Acid Sequence; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects; D005454:Fluorescence Polarization; D008081:Liposomes; D008563:Membrane Lipids / Q000737:chemistry; D008823:Micelles; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D044367:Phase Transition; D017510:Protein Folding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary
chemical_list: D023181:Antimicrobial Cationic Peptides; D008081:Liposomes; D008563:Membrane Lipids; D008823:Micelles