Discussion

Mitochondrial (mt) ATP synthase is responsible of ATP generation in most eukaryotic cells. While the procyclic form (PF) of T. brucei uses the conventional function of the enzyme, the bloodstream form (BF) exploits the reversed ATP hydrolytic activity coupled to the proton translocation across the inner mt membrane in order to maintain the mt membrane potential (ΔΨ). Despite ATP synthase overall structure and mechanism have remained conserved throughout evolution, composition of T. brucei’s peripheral stalk, which docks F1 moiety to the membrane, differs remarkably, being OSCP the only conserved subunit thereof. In other species OSCP constitutes the only physical link of the peripheral stalk to F1-ATPase via an interaction with α subunit. However, critical residues for the interaction are found neither in OSCP nor in α subunit. Consequently, OSCP role in F1-ATPase immobilization remains hypothetical in T. brucei. OSCP is required for ATP synthase function in PF, as its silencing by RNAi resulted in an evident growth phenotype. In contrast, OSCP knock-down in BF or dyskinetoplastic (Dk) cell lines did not affect growth rate. ATP synthase of Dk cells cannot translocate protons due to the loss of the mt encoded proton pore subunit a. Nevertheless, ATP hydrolysis by F1-ATPase remains essential for ΔΨ by supplying ADP3-/ATP4- exchange across the mt membrane. OSCP double knockout in BF and in Dk cell lines will enable us to determine whether the F1-peripheral stalk interaction is OSCP-mediated, or involves other subunits, e.g. kinetoplastid-specific ATPaseTb2 (peripheral stalk) or p18 (F1 sector), and whether the interaction network is preserved in the reduced ATP synthase of Dk cells.