Biology subjects

Coyne, L. P.

Publications and source records attributed to Coyne, L. P..

3 recordsLinked to original sources

bioRxiv2022

Mitochondrial protein import clogging as a mechanism of disease

Mitochondrial biogenesis requires the import of >1,000 mitochondrial preproteins from the cytosol. Most studies on mitochondrial protein import are focused on the core import machinery. Whether and how the biophysical properties of substrate preproteins affect overall import efficiency is underexplored. Here, we show that protein traffic into mitochondria is disrupted by amino acid substitutions in a single substrate preprotein. Pathogenic missense mutations in adenine nucleotide translocase 1 (Ant1), and its yeast ortholog Aac2, cause the protein to accumulate along the protein import pathway, thereby obstructing general protein translocation into mitochondria. This impairs mitochondrial respiration, cytosolic proteostasis and cell viability independent of Ant1s nucleotide transport activity. The mutations act synergistically, as double mutant Aac2/Ant1 cause severe clogging primarily at the Translocase of the Outer Membrane (TOM) complex. This confers extreme toxicity in yeast. In mice, expression of a super-clogger Ant1 variant led to an age-dependent dominant myopathy that phenocopies Ant1-induced human disease, suggesting clogging as a mechanism of disease. We propose that secondary structures of mitochondrial preproteins play an essential role in preventing clogging and disease.

biochemistry↗

bioRxiv2022

Mitochondrial protein import stress potentiates neurodegeneration in a mouse model of Parkinson disease

Several genetic and environmental risk factors for Parkinsons disease have been identified that converge on mitochondria as central elements in the disease process. However, the mechanisms by which mitochondrial dysfunction contributes to neurodegeneration remain incompletely understood. Non-bioenergetic pathways of the mitochondria are increasingly appreciated, but confounding bioenergetic defects are a major barrier to experimental validation. Here, we describe a novel bioenergetics-independent mechanism by which mild mitochondrial protein import stress augments neurodegeneration. We induced this mitochondrial protein import stress in an established mouse model of Parkinsons disease expressing the A53T mutated form of -synuclein (SNCA). Mice with import stress in addition to the A53T mutation demonstrated increased size of -synuclein aggregates, co-aggregation of mitochondrial preproteins with -synuclein, and worsened neurodegeneration. Importantly, we found no evidence of bioenergetic defects in any of the mutant mice, even with the added import stress. These data suggest that mitochondrial protein import stress contributes to neurodegeneration through cytosolic proteostatic stress and co-aggregation of mitochondrial and neuropathogenic proteins independent of bioenergetics. Given that protein import efficiency is affected by many types of mitochondrial stress, our findings add a new layer to understanding why the pathogenic mitochondrial dysfunction and cytosolic protein misfolding pathways converge in neurodegenerative diseases such as Parkinsons disease.

biochemistry↗

bioRxiv2021

Mitochondrial DNA metabolism is coupled with 20S proteasome function via regulation of deoxyribonucleotide homeostasis in Saccharomyces cerevisiae

The synthesis of mitochondrial DNA (mtDNA) is not coupled with cell cycle. Previous studies have shown that the size of deoxyribonucleoside triphosphate (dNTP) pools plays an important role in regulating mtDNA replication and amplification. In yeast, dNTPs are synthesized by the cytosolic ribonucleotide reductase (RNR). It is currently poorly understood as to how RNR activity is regulated in non-dividing or quiescent cells to finely tune mtDNA metabolism to cope with different metabolic states. Here, we show that defect in the 20S proteasome drastically destabilizes mtDNA. The mtDNA instability phenotype in 20S proteasome mutants is suppressed by overexpression of RNR3 or by the deletion of SML1, encoding a minor catalytic subunit and an intrinsic inhibitor of RNR respectively. We found that Sml1 is stabilized in the 20S proteasomal mutants, suggesting that 20S affects mtDNA stability by stabilizing Sml1. Interestingly, defect in the regulatory 19S proteasomal function has only subtle effect on mtDNA stability, supporting a role of the 20S proteasome in dNTP homeostasis independent of 19S. Finally, we found that when cells are transitioned from glycolytic to oxidative growth, Sml1 level is reduced in a 20S-dependent manner. In summary, our study establishes a link between cellular proteostasis and mtDNA metabolism through the regulation of dNTP homeostasis. We propose that increased degradation of Sml1 by the 20S proteasome under respiratory conditions provides a mechanism to stimulate dNTP synthesis and promote mtDNA amplification.

genetics↗