This protein family includes Stability determinant from Escherichia coli (PaaA2) and similar proteins predominantly found in bacteria. PaaA2 is an antitoxin from prokaryotic type II toxin-antitoxin three- component module paaR2-paaA2-parE2 that belongs to the RelB- antitoxin family but lacks a DNA-binding domain. This protein shows two alpha-helices and adopts defined loop conformations when it wraps itself around the toxin ParE2 [1,2].

1: Small-angle X-ray scattering- and nuclear magnetic resonance-derived conformational ensemble of the highly flexible antitoxin PaaA2. Sterckx YG, Volkov AN, Vranken WF, Kragelj J, Jensen MR, Buts L, Garcia-Pino A, Jove T, Van Melderen L, Blackledge M, van Nuland NA, Loris R; Structure. 2014;22:854-865. PMID:24768114

2: A unique hetero-hexadecameric architecture displayed by the Escherichia coli O157 PaaA2-ParE2 antitoxin-toxin complex. Sterckx YG, Jove T, Shkumatov AV, Garcia-Pino A, Geerts L, De Kerpel M, Lah J, De Greve H, Van Melderen L, Loris R; J Mol Biol. 2016;428:1589-1603. PMID:26996937