9.A.10. The Oligomeric Probable Pore-forming SpoIIA Toxin (SpoIIA) Family
SpoIISAB is a toxin-antitoxin module encoded on the chromosomes of Bacillus subtilis and related Bacilli. The SpoIISA toxin targets the cytoplasmic membrane and induces lysis in both B. subtilis and E. coli. However, the precise manner of SpoIISA toxicity is unknown. The N-terminal, transmembrane domain of SpoIISA has three verified TMSs while the C-terminal half of the protein is hydrophilic and localized to the cytoplasmic side of the membrane (Makroczyova J et al, 2014; PMID 25039482). Using truncated SpoIISA constructs, Makroczyova et al (2014) showed that the entire transmembrane domain is required for toxicity. The evidence is consistent with the proposal that the oligomerization of this transmembrane domain is crucial for the activity of SpoIISA, possibly by forming a pore-like structure.