ABCI3, a new mitochondrial ABC transporter from Leishmania major involved in susceptibility to antimonials and infectivity [PublishAheadOfPrint]

We have identified and characterized ABCI3 as a new mitochondrial ABC transporter from Leishmania major. Localization studies using confocal microscope, surface biotinylation assay and trypsin digestion after digitonin permeabilization suggested that ABCI3 presents a dual localization in both mitochondria and plasma membrane. Using single-knock out parasites for ABCI3 (ABCI3^+/-), we provided evidence that ABCI3 is directly involved in Sb^III and metal ions susceptibility. Attempts to obtain double knock-out parasites for ABCI3 were unsuccessful, suggesting that ABCI3 could be an essential gene in L. major. ABCI3^+/- promastigotes were 5-fold more resistant to Sb^III, while ABCI3^+/- amastigotes were approximately 2-fold more resistant to Sb^V. This resistant phenotype was associated with a decreased Sb^III accumulation due to a decreased Sb^III uptake. ABCI3^+/- parasites presented higher ATP levels and generated less mitochondrial superoxide after Sb^III incubation. Finally, we have observed that ABCI3^+/- parasites showed a slightly higher infection capacity than wild-type and add-back ABCI3^+/-:3xFABCI3 parasites; however, after 72 h the number of ABC3^+/- intracellular parasites per macrophage increased significantly. Our results show that ABCI3 is responsible for Sb^III transport inside mitochondria, where it would contribute to enhance the general toxic effects caused by Sb^III. To our knowledge, ABCI3 is the first ABC transporter which is involved in susceptibility towards antimony, conferring Sb^III resistance to parasites when partially deleted.

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