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Related Concept Videos

Mitochondrial Precursor Proteins01:39

Mitochondrial Precursor Proteins

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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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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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Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
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The Proteasome01:13

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Eukaryotic cells can degrade proteins through several pathways. One of the most important among these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
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The Proteasome02:18

The Proteasome

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Eukaryotic cells can degrade proteins through several pathways. One of the most important amongst these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
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Energy to Drive Translocation01:37

Energy to Drive Translocation

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Mitochondrial protein import is powered by two distinct energy sources: ATP hydrolysis and electrochemical potential across the inner membrane. Newly synthesized precursors are bound by cytosolic chaperones of the Hsp70 family, which guide them to the import receptors on the mitochondrial surface. Utilizing the energy of ATP hydrolysis, Hsp70 chaperones transfer these precursors to the TOM receptors on the mitochondrial outer membrane.
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Functional coupling of presequence processing and degradation in human mitochondria.

Cansu Kücükköse1,2, Asli Aras Taskin1,3, Adinarayana Marada1

  • 1Faculty of Medicine, Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Germany.

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Loss of the human mitochondrial peptidase PreP severely impairs energy production and protein processing. This study reveals PreP

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Area of Science:

  • Mitochondrial biology
  • Proteostasis
  • Molecular genetics

Background:

  • Mitochondria rely on imported nuclear-encoded proteins for function.
  • Precursor proteins utilize targeting presequences removed by matrix proteases.
  • Human mitochondrial enzyme characterization, particularly PreP, is limited.

Purpose of the Study:

  • To characterize human PreP function in mitochondrial proteostasis.
  • To investigate the consequences of PreP loss in HEK293T cells.
  • To explore the role of PreP in neurological disorders.

Main Methods:

  • Generation and analysis of HEK293T PreP knockout cells.
  • Assessment of oxidative phosphorylation and gene expression.
  • Investigation of a patient-derived PreP mutation (R183Q).

Main Results:

  • PreP deficiency causes severe defects in oxidative phosphorylation.
  • Accumulation of presequence peptides inhibits MPP and precursor processing.
  • PreP knockout compromises MIP activity, suggesting PreP degrades MIP-generated peptides.
  • The PreP R183Q mutation destabilizes the enzyme, increasing degradation and aggregation.

Conclusions:

  • PreP is crucial for human mitochondrial proteostasis and function.
  • A functional coupling exists between precursor processing (MPP, MIP) and presequence degradation (PreP).
  • Impaired PreP function contributes to mitochondrial defects and may link to neurological disorders.