A predicted immunity protein with a mostly alpha-helical fold and conserved aspartate and cysteine residues and an SE motif. 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 LD-peptidase or Tox-Caspase 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