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Related Concept Videos

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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Mitochondrial Protein Sorting01:39

Mitochondrial Protein Sorting

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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.
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
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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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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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The JAK-STAT Signaling Pathway01:20

The JAK-STAT Signaling Pathway

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Several cytokine receptors have tightly bound Janus kinase or JAK proteins attached at their cytosolic tail. Small signaling molecules such as cytokines, growth hormones, or prolactins bind to the cytokine receptors and initiate their dimerization. The dimerization brings the cytosolic JAKs together that trans-phosphorylate and activates each other. The activated JAKs now phosphorylate cytosolic tails of the cytokine receptors, which serve as binding sites for adaptor proteins such as  SH2...
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Mitochondrial Membranes01:45

Mitochondrial Membranes

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A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...
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Updated: Jun 30, 2025

Merging Absolute and Relative Quantitative PCR Data to Quantify STAT3 Splice Variant Transcripts
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Structural determinants of mitochondrial STAT3 targeting and function.

Isabelle J Marié1, Tanaya Lahiri1, Özlem Önder2

  • 1Department of Pathology and Perlmutter Cancer Center, NYU Grossman School of Medicine, New York, NY, 10128, USA.

Mitochondrial Communications
|March 19, 2024
PubMed
Summary
This summary is machine-generated.

Mitochondrial Signal transducer and activator of transcription (STAT) 3 targets specific compartments and requires its amino-terminal and linker domains for mitochondrial entry. Its SH2 domain cysteines are crucial for Complex I activity, offering therapeutic targets.

Keywords:
Electron transport chainMitochondrial importStat3

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Area of Science:

  • Mitochondrial biology
  • Cellular signaling
  • Biochemistry

Background:

  • Signal transducer and activator of transcription (STAT) 3 is known for its role in cytokine signaling, shuttling between the cytoplasm and nucleus.
  • Mitochondrial STAT3 influences cellular metabolism via the respiratory electron transport chain, but its targeting mechanisms are unclear.

Purpose of the Study:

  • To elucidate the structural requirements for mitochondrial targeting and function of STAT3.
  • To identify specific domains and residues involved in STAT3's localization and activity within mitochondria.

Main Methods:

  • Differential detergent solubility assays to fractionate mitochondrial compartments.
  • Copurification studies with respiratory chain and mitochondrial translation proteins.
  • Mutational analysis to assess the role of specific STAT3 domains and residues in mitochondrial translocation and function.

Main Results:

  • Mitochondrial STAT3 is membrane-associated, partitioning into SDS-soluble and insoluble fractions.
  • The amino-terminal and an internal linker domain are essential for mitochondrial targeting.
  • Specific cysteine residues in the SH2 domain are required for STAT3's enhancement of Complex I activity, but not for translocation.
  • Phosphorylation of serine 727 and mitochondrial DNA presence are not necessary for mitochondrial localization.

Conclusions:

  • Mitochondrial STAT3 localization is regulated by distinct structural domains.
  • Specific cysteine residues in the SH2 domain are critical for STAT3's functional role in Complex I activity.
  • These findings offer potential therapeutic strategies targeting mitochondrial STAT3 in diseases like cancer.