Figure 1.
Schematic representation of the peptides.
(A) Original SB056-lin, and (B) sequence-optimized β-SB056-lin. Yellow circles indicate hydrophobic residues, blue ones positively charged amino acids, and cyan indicates the polar serine residue.
Table 1.
MIC values of SB056-lin and β-SB056-lin against two Gram-negative and two Gram-positive bacterial strains.
Table 2.
Hemolytic activities of SB056-lin and β-SB056-lin.
Figure 2.
The blue shift of tryptophan fluorescence emission |Δλ| is plotted as a function of [L]/[P] for (A) SB056-lin, and (B) β-SB056-lin, in the presence of differently charged POPC/POPG LUVs. The lower the [L]/[P] needed to reach saturation, the higher is the peptide binding affinity.
Figure 3.
(A) Conventional CD spectra of both SB056-lin and β-SB056-lin in the presence of POPC/POPG (1/1 mol/mol) SUVs. (B) SRCD spectra of both SB056-lin and β-SB056-lin in the presence of POPC/POPG (1/1 mol/mol) SUVs. SRCD spectra of (C) SB056-lin and (D) β-SB056-lin in the presence of differently charged SUVs.
Figure 4.
Solid-state NMR spectra of SB056-lin and β-SB056-lin.
The peptides were labeled at positionVal-6 with CF3-Bpg, and solid-state NMR spectra were measured at 35°C in POPC or POPG at a [L]/[P] of 25. (A) 31P-NMR spectra of oriented samples at 0° tilt. (B) 19F-NMR spectra at 0° sample tilt. (C) 19F-NMR at 90° sample tilt. The isotropic position is marked with a dashed line, and the value of the dipolar splitting is indicated along with peptide names.
Figure 5.
Summary of peptide-lipid interactions.
The proportion of anionic lipids in the vesicles is increased from top to bottom. The behavior of the original SB056-lin peptide is represented on the left hand side, and the sequence-optimized β-SB056-lin on the right. Black arrows of different length and thickness are used to indicate the different binding equilibria. SB056-lin binds only to anionic bilayers, and in a not so well-ordered β-stranded conformation. The sequence optimized β-SB056-lin, on the other hand, forms regular β-strands that self-assemble into extended β-sheets when the negative charge of the bilayer exceeds electro-neutrality of the peptide-lipid system.