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Mitochondria-Associated Degradation Pathway (MAD) Function beyond the Outer Membrane
Pin-Chao Liao1, Dana M Alessi Wolken2, Edith Serrano3
1Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA.
Abstract:
The mitochondria-associated degradation pathway (MAD) mediates ubiquitination and degradation of mitochondrial outer membrane (MOM) proteins by the proteasome. We find that the MAD, but not other quality-control pathways including macroautophagy, mitophagy, or mitochondrial chaperones and proteases, is critical for yeast cellular fitness under conditions of paraquat (PQ)-induced oxidative stress in mitochondria. Specifically, inhibition of the MAD increases PQ-induced defects in growth and mitochondrial quality and decreases chronological lifespan. We use mass spectrometry analysis to identify possible MAD substrates as mitochondrial proteins that exhibit increased ubiquitination in response to PQ treatment and inhibition of the MAD. We identify candidate substrates in the mitochondrial matrix and inner membrane and confirm that two matrix proteins are MAD substrates. Our studies reveal a broader function for the MAD in mitochondrial protein surveillance beyond the MOM and a major role for the MAD in cellular and mitochondrial fitness in response to chronic, low-level oxidative stress in mitochondria.
Insights
The mitochondria-associated degradation pathway (MAD) is crucial for yeast survival during oxidative stress. This pathway degrades damaged mitochondrial proteins, maintaining cellular and mitochondrial health.
Area of Science:
- Mitochondrial biology
- Cellular quality control
- Oxidative stress response
Background:
- Mitochondria are vital organelles susceptible to oxidative damage.
- Cellular quality control pathways manage mitochondrial integrity.
- The mitochondria-associated degradation pathway (MAD) targets outer membrane proteins for proteasomal degradation.
Purpose of the Study:
- To investigate the role of the MAD in yeast cellular fitness under oxidative stress.
- To identify novel substrates of the MAD pathway.
- To determine the broader function of MAD in mitochondrial protein surveillance.
Main Methods:
- Yeast strains with inhibited MAD were subjected to paraquat (PQ)-induced oxidative stress.
- Cellular growth, mitochondrial quality, and chronological lifespan were assessed.
- Mass spectrometry was employed to identify ubiquitinated mitochondrial proteins.
Main Results:
- The MAD pathway, not mitophagy or other quality control mechanisms, was essential for yeast fitness under PQ stress.
- Inhibiting the MAD led to impaired growth, compromised mitochondrial quality, and reduced lifespan.
- Mass spectrometry identified candidate MAD substrates in the mitochondrial matrix and inner membrane, with two matrix proteins confirmed.
Conclusions:
- The MAD pathway plays a critical role in maintaining cellular and mitochondrial fitness against chronic oxidative stress.
- MAD's function extends beyond the mitochondrial outer membrane to include matrix and inner membrane proteins.
- This pathway represents a key mechanism for mitochondrial protein surveillance and cellular health.
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