A predicted alpha/beta fold peptidase domain with a strongly conserved triad of a histidine, aspartate/asparagine and cysteine residues that are predicted to comprise the active site of the predicted peptidase. Proteins bearing this predicted toxin domain are particularly common in both intracellular and extracellular pathogens [1].

1: Polymorphic toxin systems: comprehensive characterization of trafficking modes, processing, mechanisms of action, immunity and ecology using comparative genomics. Zhang D, de Souza RF, Anantharaman V, Iyer LM, Aravind L; Biol Direct. 2012;7:18. PMID:22731697