Self-Assembly of Designed Antimicrobial Peptides in Solution and Micelles

• Published in: Biochemistry (Easton) 1997-08, Vol.36 (31), p.9540-9549
• Main Authors: Javadpour, Maryam M., Barkley, Mary D.
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Anilino Naphthalenesulfonates; Animals; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - pharmacology; Circular Dichroism; Fluoresceins; Fluorescent Dyes; Gram-Negative Bacteria - drug effects; Gram-Positive Bacteria - drug effects; Leucine Zippers; Mice; Micelles; Peptides; Phosphorylcholine - analogs & derivatives; Protein Structure, Secondary; Solutions; Thermodynamics
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi961644f

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 α-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 α-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 ΔCp = 0, whereas phenylalanine zipper formation has a small negative ΔCp , 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.