Atypical composition and structure of the mitochondrial dimeric ATP synthase from Euglena gracilis

Mitochondrial respiratory-chain complexes fromEuglenozoa comprise classical subunits described in other eukaryotes (i.e. mammals and fungi) and subunits that are restricted to Euglenozoa (e.g. Euglena gracilis and Trypanosoma brucei). Herewe studied the mitochondrial F1FO-ATP synthase (or Complex V) fromthe photosynthetic eukaryote E. gracilis in detail. The enzymewas purified by a two-step chromatographic procedure and its subunit compositionwas resolved by a three-dimensional gel electrophoresis (BN/SDS/SDS).Twenty-two different subunits were identified by mass-spectrometry analyses amongwhich the canonical α, β, γ, δ, ε, and OSCP subunits, and at least seven subunits previously found in Trypanosoma. The ADP/ATP carrierwas also associated to the ATP synthase into a dimericATP synthasome. Single-particle analysis by transmission electron microscopy of the dimeric ATP synthase indicated that the structures of both the catalytic and central rotor parts are conserved while other structural features are original. These new features include a large membrane-spanning re- gion joining the monomers, an external peripheral stalk and a structure that goes through the membrane and reaches the inter membrane space below the c-ring, the latter having not been reported for any mitochondrial F-ATPase.