Mechanism of host substrate acetylation by a YopJ family effector

Yersinia outer protein J (YopJ) family of bacterial effectors depends on a novel acetyltransferase domain to acetylate signaling proteins from plant and animal hosts. However, the underlying mechanism is unclear. Here, we report the crystal structures of PopP2, a YopJ effector produced by the plant pathogen Ralstonia solanacearum, in complex with inositol hexaphosphate (IP(6)), acetyl-coenzyme A (AcCoA), and/or substrate RRS1-R(WRKY). PopP2 recognizes the WRKYGQK motif of RRS1-R(WRKY) to position a targeted lysine in the active site for acetylation. Importantly, the PopP2 – RRS1-R(WRKY) association is allosterically regulated by IP(6) binding, suggestive of a previously unidentified role of the eukaryote-specific cofactor in substrate interaction. Furthermore, we provide evidence for the reaction intermediate of PopP2-mediated acetylation, an acetyl-cysteine covalent adduct, lending direct support to the “Ping-Pong”-like catalytic mechanism proposed for YopJ effectors. Together, our study provides critical mechanistic insights into the virulence activity of YopJ class of acetyltransferases.