FIGURE 2.

Topologies, secondary Hα shifts and NMR solution structures of θ-defensin analogues. a, the topologies of BTD-2 and its disulfide bond mutants are represented by circles, with the disulfide bonds shown as gray bars. Residues identical to those in native BTD-2 are shown as white circles, cysteine residues are shown as black circles, and α-aminobutyric acid residues are shown as gray circles. b, secondary Hα chemical shifts of the θ-defensin analogues are calculated as the difference between the measured chemical shift of each Hα proton and its respective random coil shift. Whereas θ-defensin analogues with large secondary Hα chemical shifts are highly structured, analogues with small secondary Hα chemical shifts are disordered. Regions with positive secondary Hα shifts indicate β-sheet secondary structures. c, NMR solution structures of the θ-defensin analogues are shown in line representation, with disulfide bonds in gray. The structures are shown as an ensemble of the 20 lowest energy structures after refinement.