title: Self-assembly of designed antimicrobial peptides in solution and micelles.
abstract: Hydrophobic interactions are responsible for stabilizing leucine zippers in peptides containing heptad repeats. The effects of substituting leucine by phenylalanine and alanine by glycine on the self-assembly of coiled-coils were examined in minimalist antimicrobial peptides designed to form amphipathic alpha-helices. The secondary structure of these peptides was monitored in solution and in diphosphocholine (DPC) micelles using circular dichroism spectroscopy. The leucine peptides (KLAKLAK)3 and (KLAKKLA)n (n = 3, 4) become alpha-helical with increasing concentrations of salt, peptide, and DPC. The aggregation state and equilibrium constant for self-association of the peptides were measured by sedimentation equilibrium. The glycine peptide (KLGKKLG)3 does not self-associate. The leucine peptides and phenylalanine peptides (KFAKFAK)3 and (KFAKKFA)n (n = 3, 4) are in a monomer-tetramer equilibrium in solution, with the phenylalanine zippers being 2-4 kcal/mol less stable than the equivalent leucine zippers. Thermodynamic parameters for the association reaction were calculated from the temperature dependence of the association constants. Leucine zipper formation has DeltaCp = 0, whereas phenylalanine zipper formation has a small negative DeltaCp, presumably due to the removal of the larger surface area of phenylalanine from water. Self-association of the peptides is coupled to formation of a hydrophobic core as detected using 1-anilino-naphthalene-8-sulfonate fluorescence. Carboxyfluorescein-labeled peptides were used to determine the aggregation state of (KLAKKLA)3 and (KLGKKLG)3 in DPC micelles. (KLAKKLA)3 forms dimers, and (KLGKKLG)3 is a monomer. Aggregation appears to correlate with the cytotoxicity of these peptides.
authors.affiliation: Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Javadpour
authors.forename: M D
authors.initials: MD
authors.lastname: Barkley
mesh_terms: D016475:3T3 Cells; D000817:Anilino Naphthalenesulfonates; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology; D002942:Circular Dichroism; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006090:Gram-Negative Bacteria / Q000187:drug effects; D006094:Gram-Positive Bacteria / Q000187:drug effects; D016350:Leucine Zippers; D051379:Mice; D008823:Micelles; D010455:Peptides; D010767:Phosphorylcholine / Q000031:analogs & derivatives; D017433:Protein Structure, Secondary; D012996:Solutions; D013816:Thermodynamics
chemical_list: D000817:Anilino Naphthalenesulfonates; D000900:Anti-Bacterial Agents; D005452:Fluoresceins; D005456:Fluorescent Dyes; D008823:Micelles; D010455:Peptides; D012996:Solutions; D010767:Phosphorylcholine; C024098:6-carboxyfluorescein; C028810:dodecylphosphocholine; C027132:1-anilino-8-naphthalenesulfonate