The cyclic cystine ladder in θ-defensins is important for structure and stability, but not antibacterial activity.

Residues 5, 7, 12, and 14 are alpha-aminobutyric acid (B).

Head-to-tail (Arg-Gly) cyclic peptide. Residues 5,7,12, and 14 are replaced by alpha-aminobutyric acid.

simulated annealing, torsion angle dynamics

High resolution NMR solution structure of a symmetrical theta-defensin, BTD-2

Brunger, Adams, Clore, Gros, Nilges and Read