Knockdown of F1 epsilon subunit decreases mitochondrial content of ATP synthase and leads to accumulation of subunit c

The subunit epsilon of mitochondrial ATP synthase is the only F-1 subunit without a homolog in bacteria and chloroplasts and represents the least characterized F-1 subunit of the mammalian enzyme. Silencing of the ATP5E gene in HEK293 cells resulted in downregulation of the activity and content of the mitochondrial ATP synthase complex and of ADP-stimulated respiration to approximately 40% of the control. The decreased content of the epsilon subunit was paralleled by a decrease in the F-1 subunits alpha and beta and in the F-o subunits a and d while the content of the subunit c was not affected. The subunit c was present in the full-size ATP synthase complex and in subcomplexes of 200-400 kDa that neither contained the F-1 subunits, nor the F-o subunits. The results indicate that the epsilon subunit is essential for the assembly of F-1 and plays an important role in the incorporation of the hydrophobic subunit c into the F-1-c oligomer rotor of the mitochondrial ATP synthase complex. (C) 2009 Elsevier B.V. All rights reserved.