# An alternative mechanism by which If1 prevents ATP hydrolysis by the ATP synthase subcomplex in S. cerevisiae

## TL;DR

This study reveals that the If1 peptide prevents ATP wastage by stabilizing a key mitochondrial enzyme complex under specific metabolic conditions in yeast.

## Contribution

The study identifies a novel mechanism by which If1 stabilizes the free F1 subcomplex and mitigates mitochondrial stress during glyco-oxidative metabolism.

## Key findings

- If1 is essential for maintaining the levels of the free F1 subcomplex of the ATP synthase.
- Loss of If1 leads to mitochondrial depolarizing stress under glyco-oxidative conditions.
- If1 does not affect the assembly of higher molecular weight F1F0-ATP synthase oligomers.

## Abstract

The mitochondrial F1F0-ATP synthase is crucial for maintaining the ATP/ADP balance which is critical for cell metabolism, ion homeostasis and cell proliferation. 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. Our analyses indicate that inhibitory peptides are crucial in mitigating mitochondrial depolarizing stress under glyco-oxidative metabolic conditions. Additionally, we found that the absence of If1 destabilizes the nuclear-encoded free F1 subcomplex. This mechanism highlights the role of If1 in preventing harmful ATP wastage, offering new insights into its function under physiological and pathological conditions.

If1 inhibition of ATP hydrolysis by the mitochondrial F0F1-ATP synthase is key to stabilize the free F1 subcomplex. If1 is crucial in mitigating mitochondrial depolarizing stress under glyco-oxidative metabolic conditions.

Loss of the yeast If1/Stf1 inhibitory peptides does not preclude the assembly and levels of higher molecular weight F1F0-ATP synthase oligomers.If1 is required to maintain the levels of the free F1 subcomplex.In contrast to lactate medium, where yeast growth is exclusively dependent on the mitochondrial pathway, growth on glycerol relies on the glycolysis activity.If1/Stf1 are crucial in mitigating metabolic adverse outcomes caused by mitochondrial depolarizing stress under glyco-oxidative metabolic conditions.Loss of If1/Stf1 associated with drastic loss of F1 subcomplex does not prevent the yeast to undergo ρ-/° conditions.

Loss of the yeast If1/Stf1 inhibitory peptides does not preclude the assembly and levels of higher molecular weight F1F0-ATP synthase oligomers.

If1 is required to maintain the levels of the free F1 subcomplex.

In contrast to lactate medium, where yeast growth is exclusively dependent on the mitochondrial pathway, growth on glycerol relies on the glycolysis activity.

If1/Stf1 are crucial in mitigating metabolic adverse outcomes caused by mitochondrial depolarizing stress under glyco-oxidative metabolic conditions.

Loss of If1/Stf1 associated with drastic loss of F1 subcomplex does not prevent the yeast to undergo ρ-/° conditions.

If1 inhibition of ATP hydrolysis by the mitochondrial F0F1-ATP synthase is key to stabilize the free F1 subcomplex. If1 is crucial in mitigating mitochondrial depolarizing stress under glyco-oxidative metabolic conditions.