Probable antitoxin component of a type VII toxin-antitoxin (TA) system. Neutralizes cognate toxic HEPN probably by di-AMPylation (Probable). A mixture of HepT and MntA binds nucleotides; the highest affinity is for TTP, ATP binds more tightly than ADP or AMP (PubMed:16028221). ATP + L-tyrosyl-[protein] = diphosphate + O-(5'-adenylyl)-L-tyrosyl-[protein] ATP + O-(5'-adenylyl)-L-tyrosyl-[protein] = diphosphate + O-[5'-(adenylyl-(5'->3')-adenylyl)]-L-tyrosyl-[protein] Binds 2 divalent metal cations, probably Mg(2+) in vivo, Zn(2+) ions are found in the crystal structure. Forms a complex with HepT, probably with a stoichiometry of 2:2. Belongs to the MntA antitoxin family.