Novel IF1 mechanism preventing ATP hydrolysis by the ATP synthase subcomplex in Saccharomyces cerevisiae

The mitochondrial F1F0-ATP synthase is crucial for maintaining the ATP/ADP balance which is critical for cell metabolism, ion homeostasis, cell division, proliferation and motility. This enzyme, conserved across evolution, is found in the mitochondria or chloroplasts of eukaryotic cells and the plasma membrane of bacteria. In vitro studies have shown that the mitochondrial F1F0-ATP synthase is reversible, capable of hydrolyzing instead of synthesizing ATP. In vivo, its reversibility is inhibited by the endogenous peptide If1 (Inhibitory Factor 1), which specifically prevents ATP hydrolysis in a pH-dependent manner. Despite its presumed importance, the loss of If1 in various model organisms does not cause severe phenotypes, suggesting its role may be confined to specific stress or metabolic conditions yet to be discovered. In this study, we explored the structural and physiological importances of If1 inhibitory peptides in Saccharomyces cerevisiae. Our analyses indicate that inhibitory peptides are crucial in mitigating metabolic adverse outcomes caused by mitochondrial depolarizing stress under glyco-oxidative metabolic conditions. Under glyco-oxidative metabolic state, the energy maintenance relies both on glycolysis and oxidative phosphorylation. Additionally, we found that the absence of If1 destabilizes the nuclear-encoded free F1 subcomplex. This novel mechanism of action highlights the role of If1 in preventing harmful ATP wastage, offering new insights into its function under physiological and pathological conditions.