A predicted immunity protein with an alpha+beta fold and a conserved SF motif and tryptophan residue. Proteins containing this domain are present in bacterial polymorphic toxin systems as an immediate gene neighbour of the toxin gene, usually containing a domain of the Ntox21, Ntox29 or Tox-ART-RSE-like ADP-ribosyltransferase families [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