Mutations in mitochondrial ATP6 gene encoding subunit of ATP synthase and their impact on cell physiology in yeast S. cerevisiae

Yeast plays an important role as a model system to study the biochemistry and molecular biology of mitochondria. We have used yeast cells to understand how several mutations in mitochondrial ATP6 gene, leading to mitochondrial disorders or present in cancer cells, impact the ATP synthase. The consequences of ATP6 pathological mutations in yeast corresponded to the reported severity of these mutations in patients, likely reflecting a high level of evolutionary conservation of Atp6p. Surprisingly, the ATP6 gene mutations found in cancer cells, although affecting conserved amino acids of Atp6p, have little, if any, effect on energetic activity of mitochondria. We have analyzed further two cancer related mutations: Atp6-K90E and Atp6-P163S. In yeast cells these mutations lead to highly elevated reactive oxygen species (ROS) and hypersensitivities to several stresses induced by rapamycin, homocysteine, nystatin or calcium ions in OM45-GFP strain background. The energetic activity of OXPHOS system is not defective in atp6-K90E or atp6-P163S OM45-GFP strains, except the hydrolytic activity of ATP synthase. This indicates that rather the mechanisms detoxifying ROS, than the OXPHOS deficiencies, are the source of ROS elevation. The Om45 is a mitochondrial protein of the intermembrane space attached by its N-terminal part to the Por1p through Om14 protein. The Por1 protein is the yeast homolog of mammalian VDAC protein (Voltage-Dependent Anion Channel) and play a key role in mediating mitochondrial outer membrane permeability to small metabolites, including ATP, ADP, and AMP. The function of Om14-Om45 protein complex is not known, although it was shown that Om45p interacts physically with many transporters of the inner mitochondrial membrane and ATP synthase subunits. The observed phenotypes of double atp6-K90E or atp6-P163S OM45-GFP mutants indicate the role of ATP synthase in ROS regulation and cell physiology.