eIF5A controls mitoprotein import by relieving ribosome stalling at TIM50 translocase mRNA

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Efficient import of nuclear-encoded proteins into mitochondria is essential for cellular energy production.
• The translation factor eukaryotic initiation factor 5A (eIF5A) is known to resolve ribosome stalling at polyproline sequences.
• The precise role of eIF5A in mitochondrial function and protein import remains largely undefined.

Purpose of the Study:

• To elucidate the molecular mechanism by which eIF5A influences mitochondrial function.
• To investigate the impact of eIF5A on the translation and import of mitochondrial proteins.
• To identify specific targets of eIF5A involved in mitochondrial protein import.

Main Methods:

• Yeast models with depleted eIF5A were utilized.
• Quantitative analysis of protein translation and levels, focusing on TCA cycle and oxidative phosphorylation proteins.
• Investigation of cytosolic accumulation of mitochondrial protein precursors.
• Identification of direct mRNA targets of eIF5A using ribosome profiling and immunoprecipitation assays.
• Functional analysis of mutations in target proteins, such as Tim50.

Main Results:

• eIF5A depletion led to reduced translation and levels of key mitochondrial proteins involved in energy metabolism.
• Loss of eIF5A resulted in the accumulation of mitochondrial protein precursors in the cytosol, indicating impaired import.
• A mitochondrial inner membrane protein, Tim50, containing a polyproline region, was identified as a direct target of eIF5A.
• eIF5A alleviates ribosome stalling on Tim50 mRNA, facilitating co-translational import.
• Altering polyproline stretches in Tim50 partially rescued mitochondrial import defects and gene expression.

Conclusions:

• eIF5A plays a critical role in mitochondrial function by promoting efficient translation and co-translational import of nuclear-encoded mitochondrial proteins.
• The mechanism involves alleviating ribosome stalling at polyproline-rich regions in mRNAs, exemplified by Tim50.
• This regulation is crucial for maintaining mitochondrial integrity and cellular respiration, highlighting a direct link between translation regulation and mitochondrial protein import.