Fig. 3: WF peptides do not adopt ideal α-helix conformations in models of bacterial plasma membranes.

Far-UV circular dichroism spectra of 50 µM Winter Flounder peptides or temporin L in 5 mM Tris buffer at pH with 5 mM SDS micelles (a) or 15 µM in models of Gram-positive (3 mM POPG—b) or Gram-negative (3 mM POPE:POPG (75:25)—c) bacterial plasma membranes at 37 °C. Spectra are representative of three independently repeated experiments. A comparison of H_N to H_A NOESY cross peak linewidths (mean and SD) for WF AMPs and temporin L (TL) in SDS_d25 reveals much greater linewidths for the WF peptides, indicative of intermediate exchange (d). Newly solved structures of the WF AMPs are likely hybrids of at least two conformations adopted in SDS (f) and lower proportions of α-helix conformation are identified relative to previously solved structures of WF2 (2LS9) and, particularly, temporin L (6GS5) (e). Segments are coloured purple for α-helix, blue for 3-₁₀ helix and cyan and white respectively for turns and coils. Note however that Define Secondary Structure of Proteins (DSSP) is incapable of identifying P_II conformation. One-way ANOVA with Bonferroni’s multiple comparisons test: *p < 0.05; **p < 0.01; ****p < 0.0001.