Membrane contact sites are regions of close apposition between two organelles, typically less than 30 nanometers apart, that facilitate transfer of biomolecules. The presence of contact sites has been demonstrated in yeast, plants, and mammalian cells. Here, we investigated the presence of such contact sites in Trypanosoma brucei. In mammalian cells, endoplasmic reticulum-mitochondria contact sites facilitate mitochondrial uptake of Ca2+ released by the ER-located inositol 1,4,5-trisphosphate receptor (InsP₃R). However, the InsP₃R in trypanosomes localizes to acidocalcisomes, which serve as major Ca2+ stores in these parasites. In this work, we have used super-resolution structured illumination microscopy and electron microscopy to identify membrane contact sites that exist between acidocalcisomes and mitochondria. Furthermore, we have confirmed the close association of these organelles using proximity ligation assays. Characterization of these contact sites may be a necessary starting point towards unraveling the role of Ca2+ in regulating trypanosome bioenergetics.
Keywords: calcium signaling; membrane contact sites; trypanosomes.