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Related Concept Videos

Protein Transport into the Inner Mitochondrial Membrane01:34

Protein Transport into the Inner Mitochondrial Membrane

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Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation.
Transport of mitochondrial precursors across the TIM23 channel is driven by...
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Mitochondrial Protein Sorting01:39

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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 ADP/ATP Carrier Protein01:42

The ADP/ATP Carrier Protein

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ADP/ATP carrier or AAC protein is the most abundant carrier protein in the inner mitochondrial membrane. It transports large quantities of ADP and ATP, equivalent to the average human body weight, every day. Among other transporters, ACC protein is one of the best-studied members of the mitochondrial carrier protein family. The ADP/ATP carrier protein comprises two transmembrane helices connected to a loop and a single alpha-helix on the matrix side. It switches between two conformational...
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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.
Generally, polypeptides are unfolded by two distinct...
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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.
Most of the mitochondrial...
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Assessment of Open Probability of the Mitochondrial Permeability Transition Pore in the Setting of Coenzyme Q Excess
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Hem25p is a mitochondrial IPP transporter.

Jonathan Tai1,2,3, Rachel M Guerra3, Sean W Rogers3

  • 1Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.

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|March 30, 2023
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Summary
This summary is machine-generated.

Mitochondria use Hem25p, a protein involved in heme production, to transport isopentenyl pyrophosphate (IPP) for Coenzyme Q (CoQ) biosynthesis. This discovery solves a long-standing mystery in cellular metabolism.

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Area of Science:

  • Cell Biology
  • Biochemistry
  • Mitochondrial Biology

Background:

  • Coenzyme Q (CoQ, ubiquinone) is vital for cellular respiration, requiring isoprenoid precursors for its synthesis.
  • The mechanism by which mitochondria acquire cytosolic isoprenoids for CoQ biosynthesis remains largely unknown.

Approach:

  • Utilized genetic screening, metabolic tracing, and targeted uptake assays in *Saccharomyces cerevisiae*.
  • Investigated the role of Hem25p, a known mitochondrial glycine transporter, in isoprenoid transport.
  • Performed heterologous expression of Hem25p in *Escherichia coli* to confirm transport function.

Key Points:

  • Hem25p functions as an isopentenyl pyrophosphate (IPP) transporter, facilitating its uptake into mitochondria.
  • Mitochondria lacking Hem25p exhibit impaired IPP incorporation into CoQ precursors, resulting in CoQ deficiency.
  • Hem25p is sufficient for IPP transport, as demonstrated by its functional expression in *E. coli*.

Conclusions:

  • Hem25p is the primary transporter of mitochondrial isoprenoids essential for Coenzyme Q biosynthesis in yeast.
  • This finding elucidates a critical step in CoQ production and highlights a dual role for Hem25p.