Figure 1.

The NMR structures of TI and cTI (red), TII and cTII (cyan), TIII and cTIII (magenta). (a) Secondary αH chemical shift at 298 K determined from ¹H NMR spectra. Shifts were calculated by subtraction of random coil ¹H NMR shifts [41] from the experimental values. For tachyplesin I (TI), the shifts of the peptide synthesized in our lab were compared to shifts obtained from data banks: TI—PDB ID 2RTV [37], and TI—BMRB ID 1135 [38]. Positive shifts greater than 0.1 ppm suggest β-strands, indicated by grey arrows. (b) Overlay of the cyclic analogues (colored backbone) with their respective parent peptide (grey backbone). Hydrogen bonds between β-strands are indicated in blue. The structure of TI was obtained from the PDB (ID 1WO0). (c) Overlay of TI–TIII and cTI–cTIII. (d) Mobility of the residues (K or R) at position 1 and 15, which differ between the peptides, and of W2 of the native sequences and cyclic analogues, respectively.