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Widespread use of unconventional targeting signals in mitochondrial ribosome proteins

Yury S Bykov1, Tamara Flohr2, Felix Boos2

  • 1Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.

The EMBO Journal
|November 17, 2021
PubMed

Insights

Mitochondrial ribosomal proteins (MRPs) lacking typical N-terminal signals can still enter mitochondria. This study identifies internal targeting signals in yeast MRPs, revealing a more versatile mitochondrial protein import mechanism.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Mitochondrial ribosomes (MRPs) are crucial for cellular respiration.
  • MRP assembly requires importing nuclear-encoded proteins into the mitochondrial matrix.
  • A significant portion of yeast MRPs lack conventional N-terminal mitochondrial targeting signals (MTSs).

Purpose of the Study:

  • To investigate the import mechanisms of yeast MRPs lacking canonical MTSs.
  • To identify and characterize internal MTSs in these proteins.
  • To understand the implications for mitochondrial protein targeting versatility.

Main Methods:

  • In vivo experimental characterization of 15 yeast MRPs.
  • Analysis of the conserved MRP Mrp17/bS6m.
  • Investigation of sequence properties mediating mitochondrial import.

Main Results:

  • Five out of 15 characterized yeast MRPs utilize internal MTSs for import.
  • The internal targeting signal of Mrp17/bS6m mediates binding to TOM complexes.
  • Positive charges within the Mrp17 sequence facilitate translocation, a property not predictable by standard methods.

Conclusions:

  • Mitochondrial protein targeting is more versatile than previously assumed.
  • Internal MTSs represent an alternative import pathway for specific mitochondrial proteins.
  • Ribosome assembly constraints may have driven the evolution of internal targeting signals in MRPs.
Keywords:
mitochondriamitochondrial ribosomemitochondrial targeting signaltargetingtranslocation

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