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Related Concept Videos

Mitochondrial Precursor Proteins01:39

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Mitochondrial precursors are partially unfolded or loosely folded polypeptide chains. Newly synthesized precursors are inhibited from spontaneously folding into their native conformation by the cytosolic chaperones, heat shock proteins 70 (Hsp70), and mitochondrial import stimulation factors (MSFs). Precursors bound to MSFs are guided to the TOM70-TOM37 receptors, while precursors bound to Hsp70  chaperones are targetted to TOM20-TOM22 receptor complexes.
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Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
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Nuclear protein sorting regulates nucleus composition and gene expression, crucial for determining the fate of a eukaryotic cell. Hence, the entry and exit of molecules across the nuclear envelope is a tightly controlled process. Nuclear protein sorting can be inhibited by one of the following ways: 1) masking cargo signal sequences, 2) modifying the nuclear receptor's affinity for cargo, 3) controlling the nuclear pore size, 4) retaining the cargo during its transit to the cytosol or the...
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The Upf proteins that carry out nonsense-mediated decay (NMD) are found in all eukaryotic organisms, including humans. Each protein has an individual role, but they need to work in collaboration. Upf1 is an ATP-dependent RNA helicase that unwinds the RNA helix. Because Upf1 can unwind any RNA, Upf2 and Upf3 are required to help Upf1 discriminate between nonsense and normal mRNAs.
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Mitochondria are double-membrane organelles of the eukaryotes involved in cellular metabolism, signaling, ATP synthesis, and programmed cell death.  Each of these processes requires specific proteins and enzymes that must be correctly sorted to the right mitochondrial subcompartment for the proper functioning of the organelle.
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Nuclear protein sorting is the selective trafficking of histones, polymerases, gene regulatory proteins into the nucleus and exporting RNAs and ribosomes to the cytosol. It is a tightly controlled process that regulates gene expression within a cell.
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Rapid Isolation of the Mitoribosome from HEK Cells
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An avoidance segment resolves a lethal nuclear-mitochondrial targeting conflict during ribosome assembly.

Michaela Oborská-Oplová1,2, Alexander Gregor Geiger2, Erich Michel3

  • 1Institute of Biochemistry, ETH Zurich, Zurich, Switzerland.

Nature Cell Biology
|January 31, 2025
PubMed
Summary
This summary is machine-generated.

A newly discovered mitochondrial avoidance segment (MAS) in ribosomal protein uS5 prevents mistargeting to mitochondria. This crucial cellular sorting mechanism ensures proper ribosome assembly and prevents lethal errors in protein targeting.

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Evolutionary Biology

Background:

  • Cellular targeting pathways face challenges in sorting ribosomal proteins.
  • Ribosome production requires precise protein localization to the nucleus or mitochondria.
  • Mitochondrial and nuclear targeting machinery can conflict.

Purpose of the Study:

  • To identify mechanisms resolving conflicts in cellular targeting pathways.
  • To investigate the role of cytosolic ribosomal protein uS5 in protein sorting.
  • To understand the evolutionary significance of mitochondrial avoidance.

Main Methods:

  • Identification and characterization of a conserved mitochondrial avoidance segment (MAS) in uS5.
  • Analysis of uS5 mistargeting upon MAS removal.
  • Assessment of rescue strategies by impairing mitochondrial import.
  • Investigation of MAS function in triaging nuclear targeting.

Main Results:

  • A conserved mitochondrial avoidance segment (MAS) was discovered in uS5.
  • MAS removal caused uS5 mistargeting to mitochondria, disrupting cytosolic ribosome assembly.
  • Lethality from MAS removal was rescued by impairing mitochondrial import.
  • MAS was shown to disable a cryptic mitochondrial targeting activity within uS5.

Conclusions:

  • MAS is essential for preventing fatal capture of uS5 by mitochondria.
  • MAS ensures accurate nuclear targeting, reinforcing organelle targeting fidelity.
  • MAS represents a key evolutionary acquisition for early eukaryotes developing endosymbiosis.