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Mitochondrial presequences harbor variable strengths to maintain organellar function.

Youmian Yan1, Baigalmaa Erdenepurev1, Ian Collinson2

  • 1Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA.

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|June 12, 2025
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Summary
This summary is machine-generated.

Mitochondrial protein presequences vary in "strength," affecting import efficiency and cellular fitness. This study quantifies presequence strength, revealing broader impacts beyond stress signaling and highlighting the need for nuanced characterization.

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Area of Science:

  • Mitochondrial Biology
  • Protein Import
  • Cellular Homeostasis

Background:

  • Mitochondrial proteins require N-terminal presequences for targeting and import.
  • Presequences are generally amphipathic helices but lack a consensus motif, leading to variable import efficiencies.
  • The concept of presequence 'strength' is crucial for models of cellular stress sensing, but lacks quantitative definition.

Purpose of the Study:

  • To quantitatively analyze the factors determining mitochondrial presequence strength.
  • To investigate the impact of presequence strength on mitochondrial function and cellular fitness.
  • To explore the broader implications of presequence strength variability in cellular processes.

Main Methods:

  • Utilized the high-throughput MitoLuc assay to quantify multiple aspects of presequence strength.
  • Assessed import efficiencies under basal and stressed (mitochondrial uncoupling) conditions.
  • Evaluated the ability of different presequences to rescue respiratory growth defects in Complex IV-deficient yeast.

Main Results:

  • Identified differential import efficiencies conferred by select presequences, including those involved in the mitochondrial unfolded protein response (UPRmt).
  • Demonstrated that presequence strength significantly impacts import efficiency in both stressed and non-stressed conditions, extending beyond known stress-related functions.
  • Showed that only robust presequences could fully rescue respiratory growth defects, linking presequence strength to metabolic potential.

Conclusions:

  • Presequence strength is a multifaceted characteristic, encompassing total imported protein, import velocity, and sensitivity to uncoupling.
  • The annotation of presequences as 'weak' or 'strong' requires more nuanced characterization.
  • Variability in presequence strength significantly influences cellular fitness beyond stress signaling, suggesting a broad role in fine-tuning mitochondrial import and homeostasis.