ABC toxins from pathogenic bacteria are pore-forming toxins that selectively bind to and deliver cytotoxic enzymes to target cells. Classically they are encoded by three distinct tc genes that encode the pore-forming, enzymatic and toxin encapsulating components, respectively. Tropism is associated with the pore-forming A subunit. The ABC toxin from the invertebrate pathogen Yersinia entomophaga (YenTc) is unusual in that it is the product of a pathogenicity island that contains seven tc-like genes, of which six are minimally required to produce a functional toxin, and four of which encode for the pore-forming A subunit. We have recently used single particle cryo-EM to determine structures of both the 2.1 MDa, pore-forming A subunit of YenTc, as well as the 2.4 MDa YenTc holotoxin. We studied both complexes in two different conformational states, reflecting the soluble, oligomeric pre-pore and the membrane embedded pore forming state. Comparison of the pre-pore and pore conformations provides insights into how the toxin is gated, as well as candidate structural motifs that are important for membrane binding and host recognition. Expanding the scope of our studies to include the entire, functional holotoxin reveals important details about the interface between the toxin encapsulating BC cage and the pore-forming A subunit, as well as identifying the way that the cytotoxic payload is packaged and translocated. Finally, the unique architecture of the pore-forming A subunit of YenTc compared to other ABC toxins provides insights into the evolution of host specificity.