| Leishmania sp. are human parasites with several single-copy organelles, which include the nucleus, Golgi apparatus and the mitochondrion. Mitochondria are implicitly relevant to the cell in various processes including ATP generation, lipid metabolism, developmental, and apoptotic processes. Essentially, the two forces fission and fusion control their number, size and shape in a cell. Mostly studied in yeast and animals, the process of fission is conserved throughout evolution with orthologs of two prominent proteins identified in all, FIS1 and the dynamin-like protein DNM1/DRP1. Mitochondrial fission is relevant for Leishmania proper segregation and hence for its proliferation, survival, and virulence. However, little is known about the biogenesis and dynamics of this organelle in this parasite. The goal of this study is to identify and characterize the core proteins involved in fission of the mitochondrion in Leishmania major. BLAST search of L. major genome lead to the identification of a human hFIS1 ortholog, LmFIS, which is one of the proteins involved in mitochondrial dynamics. LmFIS shares homology only within the TPR motif, and is more than double the size of FIS1 orthologs of other organisms. LmFIS induces mitochondrial fission in mammalian cells but not in yeast. Leishmania expresses a shorter version of LmFIS that was named LmFIS-S. LmFIS-S is expressed in dividing and stationary phase promastigotes. Unlike yeast and mammalian orthologs, it does not behave as an integral membrane protein in Leishmania but rather like a soluble protein. Further, the LmFIS gene seems to be essential to Leishmania viability as no null mutants could be obtained. Native gel electrophoresis demonstrated that LmFIS-S belongs to several multimeric protein complexes, suggesting that it interacts with other proteins. In addition, two yeast orthologs involved in mitochondrial fission were identified in L. major, LmMDV1 and LmDLP. Both LmMDV1 and LmDLP are soluble cytosolic and partially membrane associated, which is consistent with the idea that they may be recruited to the membrane for organellar fission. Biochemical evidences indicate that LmFIS-S interacts with LmMDV1. The present data suggest that the mitochondrial fission apparatus in Leishmania resembles the yeast system and differs from that of mammals. This disparity can be exploited for the development of new chemotherapeutics against leishmaniasis. |
