ABCI3 Is a New Mitochondrial ABC Transporter from Leishmania major Involved in Susceptibility to Antimonials and Infectivity.

We have identified and characterized ABCI3 as a new mitochondrial ABC transporter from Leishmania major Localization studies using confocal microscopy, a surface biotinylation assay, and trypsin digestion after digitonin permeabilization suggested that ABCI3 presents a dual localization in both mitochondria and the plasma membrane. From studies using parasites with a single knockout of ABCI3 (ABCI3+/-), we provide evidence that ABCI3 is directly involved in susceptibility to the trivalent form of antimony (SbIII) and metal ions. Attempts to obtain parasites with a double knockout of ABCI3 were unsuccessful, suggesting that ABCI3 could be an essential gene in L. majorABCI3+/- promastigotes were 5-fold more resistant to SbIII than the wild type, while ABCI3+/- amastigotes were approximately 2-fold more resistant to pentavalent antimony (SbV). This resistance phenotype was associated with decreased SbIII accumulation due to decreased SbIII uptake. ABCI3+/- parasites presented higher ATP levels and generated less mitochondrial superoxide after SbIII incubation. Finally, we observed that ABCI3+/- parasites showed a slightly higher infection capacity than wild-type and add-back ABCI3+/-::3×FABCI3 parasites; however, after 72 h the number of ABCI3+/- intracellular parasites per macrophage increased significantly. Our results show that ABCI3 is responsible for SbIII transport inside mitochondria, where it contributes to enhancement of the general toxic effects caused by SbIII To our knowledge, ABCI3 is the first ABC transporter which is involved in susceptibility toward antimony, conferring SbIII resistance to parasites when it is partially deleted.