Probable antitoxin component of a type II toxin-antitoxin (TA) system. In vivo probably neutralizes the toxic effect of cognate toxin Res. Homodimer. Forms a complex with cognate toxin Res; the 2 toxin molecules dimerize and each contacts an Xre homodimer. Most Res-Xre contacts are between the antitoxin molecule closest to the toxin. The homodimer can be superposed on the Cro helix-turn-helix binding domain, suggesting it probably binds DNA and can act as a transcription factor as is often the case with antitoxins in type II TA systems (Probable). The C-terminus of the antitoxin inserts into the putative NAD(+)-binding site of toxin Res, blocking access to the active site (PubMed:30315706). Belongs to the MbcA/ParS/Xre antitoxin family.