Involved in the export of the LtxA leukotoxin. Probably part of a complex composed of LtxB, LtxD and TdeA, which forms a single transport channel across the two membranes. Levels of toxin expression vary greatly among strains. Highly leukotoxic strains (JP2-type strains) produce more LtxA protein and ltx mRNA than minimally leukotoxic strains (652-type strains). Variations are probably due to different types of promoters. Mutation has no effect on the levels of leukotoxin mRNA, but mutants have significantly less total leukotoxin than the parent strain. Belongs to the membrane fusion protein (MFP) (TC 8.A.1) family.