The bacterial antitoxin HipB establishes a ternary complex with operator DNA and phosphorylated toxin HipA to regulate bacterial persistence

Nearly all bacteria exhibit a type of phenotypic growth described as persistence that is thought to underlie antibiotic tolerance and recalcitrant chronic infections. The chromosomally encoded high-persistence (Hip) toxin–antitoxin proteins HipA(SO) and HipB(SO) from Shewanella oneidensis, a proteobacterium with unusual respiratory capacities, constitute a type II toxin–antitoxin protein module. Here we show that phosphorylated HipA(SO) can engage in an unexpected ternary complex with HipB(SO) and double-stranded operator DNA that is distinct from the prototypical counterpart complex from Escherichia coli. The structure of HipB(SO) in complex with operator DNA reveals a flexible C-terminus that is sequestered by HipA(SO) in the ternary complex, indicative of its role in binding HipA(SO) to abolish its function in persistence. The structure of HipA(SO) in complex with a non-hydrolyzable ATP analogue shows that HipA(SO) autophosphorylation is coupled to an unusual conformational change of its phosphorylation loop. However, HipA(SO) is unable to phosphorylate the translation factor Elongation factor Tu, contrary to previous reports, but in agreement with more recent findings. Our studies suggest that the phosphorylation state of HipA is an important factor in persistence and that the structural and mechanistic diversity of HipAB modules as regulatory factors in bacterial persistence is broader than previously thought.