Specific Enterobacteriaceae produce antimicrobial peptides under nutrient limited conditions. Antimicrobial peptide microcin J25 (MccJ25) has a unique lasso topology. MccJ25 expression is upregulated during iron limiting conditions and imported by an iron importer (FhuA), consequently killing the bacterium. Providing MccJ25 producing cells with an advantage over other cells under nutrient limited conditions. Mature toxic MccJ25 secretion and self-immunity is conferred by an ATP-binding cassette (ABC) exporter McjD. The X-ray crystal structure of McjD from E. coli was determined at 2.7 Å resolution, the first structure of an antibacterial peptide ABC transporter. McjD was observed in a new conformation of nucleotide-bound outward-occluded, defining a clear ligand cavity for ABC exporters for the first time. The new conformation shows similarities to both inward-open MsbA and outward-open Sav1866 structures. An almost rigid rotation of TMs 1 and 2 from an outward-open conformation towards the equivalent TMs of the opposite monomer forms the outward-occluded conformation. This conformation has been confirmed by cysteine cross-linking studies. Therefore, we propose that the outward-occluded state represents an intermediate conformation between the outward-open and inward-open conformation of ABC exporters. Biochemical analyses also demonstrate McjD-dependent immunity to MccJ25 through efflux of the peptide. McjD was shown to be able to directly bind MccJ25. McjD displays a basal ATPase activity that can be stimulated by MccJ25.