Acute hepatopancreatic necrosis disease (AHPND) is an emerging shrimp disease that represents a significant threat to the shrimp farming industry, causing ~7 billion USD in damage annually. Further, AHPND causes 100% mortality in farmed shrimp, where treatment is reliant on antibiotics, ultimately contributing to the wider issue of antibiotic resistance. AHPND is caused by a virulent strain of Vibrio parahaemolyticus (Vp) that harbours the Photorhabdus insect-related pore-forming toxin, PirAB. However, the complex architecture and mechanism of action of PirAB remains elusive, thereby limiting our ability to develop effective therapeutics for improved aquaculture outcomes.
Here, using an in tandem PirAB operon construct, we determine the first cryo-EM structure of PirAB in complex as a 2.61 Å heterodimer and a 2.84 Å heterodecamer. Excitingly, while this heterodimer structure resembles an Alphafold prediction, this complex may represent the active form that targets shrimp. Moreover, we hypothesise the heterodecamer, which is composed of 6 PirA and 4 PirB, forms a novel pre-activated package assembly that is delivered from Vp. Accordingly, PirAB induces membrane disruption as shown through liposome dye leakage, indicative of pore formation. Collectively, our findings provide new insight into how Pir protein assembly is reliant on the genetic signature to form important interactions for complex formation and pore assembly. These results will help guide the design of inhibitors against PirAB, reducing AHPND prevalence in the shrimp farming industry.