Subcomplexes of human ATP synthase mark mitochondrial biosynthesis disorders

OBJECTIVE: Methods: We describe biochemically and clinically relevant aspects of mitochondrial ATP synthase, the enzyme that supplies most ATP for the cells energy demand. RESULTS: Analyzing human Rho zero cells we could identify three subcomplexes of ATP synthase: F1 catalytic domain, F1 domain with bound natural IF1 inhibitor protein, and F1-c subcomplex, an assembly of F1 domain and a ring of F(O)-subunits c. Large amounts of F1 subcomplexes accumulated also in mitochondria of patients with specific mitochondrial disorders. By quantifying the F1 subcomplexes and other oxidative phosphorylation complexes in parallel, we were able to discriminate three classes of defects in mitochondrial biosynthesis, namely, mitochondrial DNA depletion, mitochondrial transfer RNA (tRNA) mutations, and mutations in the mitochondrial ATP6 gene. INTERPRETATION: The relatively simple electrophoretic assay used here is a straightforward approach to differentiate between various types of genetic alterations affecting the biosynthesis of oxidative phosphorylation complexes and will be useful to guide molecular genetic diagnostics in the field of mitochondrial neuromuscular disorders.