Loading...
Novel Pathways Suppressing the Deleterious Effects of Mitochondrial Protein Import Clogging
Mishra, Gargi
Mishra, Gargi
Citations
Altmetric:
Journal Title
Keywords
Readers/Advisors
Journal Title
Term and Year
Publication Date
2026-02-24
Type
Book Title
Publication Volume
Publication Issue
Publication Begin
Publication End
Number of pages
Files
Research Projects
Organizational Units
Journal Issue
Abstract
Mitochondria perform diverse cellular functions beyond ATP production, including calcium handling, innate immune signaling, and cell death regulation. Increasing evidence indicates that mitochondrial dysfunction can arise independently of bioenergetic failure. In particular, defects in mitochondrial protein import can cause the toxic accumulation of unimported precursors in the cytosol, triggering mitochondrial precursor overaccumulation stress (mPOS) and ultimately leading to cell death. Because ~99% of the mitochondrial proteome is nuclear encoded, maintaining protein import fidelity is a major cellular challenge. Several human diseases previously attributed solely to impaired mitochondrial function are now understood to arise from protein import defects. One especially deleterious form of import defect occurs when precursor proteins become lodged within the import translocases, a phenomenon termed mitochondrial protein import clogging. In this thesis, I used Saccharomyces cerevisiae to identify and characterize cellular pathways that either alleviate mitochondrial protein import clogging or enable adaptation to mPOS. Using genetic screens, transcriptomic profiling, and proteomic approaches, I identified two distinct protective pathways. The first centers on the mitochondrial F-box protein Mfb1 and the cytosolic heat shock protein Hsp31, the yeast homolog of human DJ-1. I show that MFB1 overexpression rescues growth and import defects under multiple mPOS-inducing conditions, whereas MFB1 loss exacerbates precursor accumulation, mtDNA instability, and proteostatic stress. Mechanistically, Mfb1 localizes near the mitochondrial protein import machinery and appears to support import competency at the mitochondrial surface, while Hsp31 acts downstream as a cytosolic proteostatic buffer in Mfb1-deficient cells to alleviate mPOS under import clogging conditions. The second pathway involves the RNA-binding proteins Pbp1 and Pab1, key components of stress granules. Through a multicopy suppressor screen, I found that PBP1 and PAB1 robustly suppress petite colony formation, likely by restoring mitochondrial integrity under severe import clogging conditions. Transcriptomic, proteomic, and RNA interactomic analyses revealed that mitochondrial protein import clogging dramatically reduces the interaction networks of Pbp1. Pbp1 dosage strongly modulates transcriptional programs governing mitochondrial biogenesis, iron homeostasis, and cellular metabolism in a manner dependent on import state. Together, this work defines two complementary adaptive strategies that protect cells from mitochondrial protein import clogging: a mitochondrial surface quality-control pathway mediated by Mfb1, a cytosolic proteostasis pathway involving Hsp31, and a condensate-driven pathway involving Pbp1. These findings establish mechanistic links between mitochondrial protein import fidelity, cytosolic proteostasis, RNA biology, and mitochondrial genome stability, with implications for understanding mitochondrial disease and neurodegenerative disorders.
Citation
DOI
Description
Accessibility Statement
If this SOAR repository item is not accessible to you (e.g. able to be used in the context of a disability), please email libsuppt@upstate.edu.