Subcomplexes of human ATP synthase mark mitochondrial biosynthesis disorders

Abstract

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. Ann Neurol 2006