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Related Concept Videos

Mitochondrial Precursor Proteins01:39

Mitochondrial Precursor Proteins

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 precursors...
Mitochondrial Protein Sorting01:39

Mitochondrial Protein Sorting

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...
Energy to Drive Translocation01:37

Energy to Drive Translocation

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...
Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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,...
Mitochondrial Membranes01:45

Mitochondrial Membranes

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,...
Mitochondrial Membranes01:45

Mitochondrial Membranes

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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Understanding the Changes in Mitochondrial Morphology through Dynamic and Three-dimensional Fluorescence Micrographs
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Tom20 recognizes mitochondrial presequences through dynamic equilibrium among multiple bound states.

Takashi Saitoh1, Mayumi Igura, Takayuki Obita

  • 1Division of Structural Biology, Medical Institute of Bioregulation, Kyushu University, Maidashi, Higashi-ku, Fukuoka, Japan.

The EMBO Journal
|October 20, 2007
PubMed
Summary
This summary is machine-generated.

Mitochondrial protein import relies on Tom20 recognizing presequences. Structural studies revealed Tom20 interacts dynamically with diverse presequences through multiple binding modes, explaining its broad selectivity.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Background:

  • Mitochondrial proteins are synthesized in the cytosol and imported into mitochondria.
  • The N-terminal presequences of mitochondrial precursor proteins contain a consensus motif recognized by the mitochondrial receptor Tom20.

Purpose of the Study:

  • To elucidate the structural basis for the broad selectivity of the Tom20 receptor.
  • To understand how Tom20 recognizes diverse mitochondrial presequences.

Main Methods:

  • Crystallization of the Tom20-presequence complex using disulfide bond tethering.
  • Analysis of two crystal structures with different linker designs.
  • Nuclear Magnetic Resonance (NMR) 15N relaxation analyses to probe dynamics.

Main Results:

  • Two distinct crystal structures revealed different orientations of the presequence relative to Tom20.
  • Neither crystal structure fully explained the hydrophobic preference of the consensus motif.
  • NMR data indicated dynamic motion at the Tom20-presequence interface on a sub-millisecond timescale.

Conclusions:

  • A dynamic equilibrium among multiple binding states is proposed to explain Tom20's broad selectivity.
  • The interaction between Tom20 and mitochondrial presequences is dynamic and involves multiple modes.
  • This dynamic interaction mechanism facilitates the recognition of diverse mitochondrial presequences by Tom20.