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Related Concept Videos

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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The Inner Mitochondrial Membrane01:28

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The inner mitochondrial membrane is the primary site of ATP synthesis. The inner membrane domain that forms a smooth layer adjacent to the outer membrane is called the inner boundary membrane. This domain contains membrane transporters that drive metabolites in and out of the mitochondria.  In contrast, the inner membrane network that invaginates into the matrix space is called the cristae membrane. This domain accounts for principle mitochondrial function as it accommodates the protein...
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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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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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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.
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Structure of Porins01:21

Structure of Porins

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Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a  motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel...
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Related Experiment Video

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Multi-parameter Measurement of the Permeability Transition Pore Opening in Isolated Mouse Heart Mitochondria
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Multi-parameter Measurement of the Permeability Transition Pore Opening in Isolated Mouse Heart Mitochondria

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The mitochondrial permeability transition pore.

M Crompton1, S Virji, V Doyle

  • 1Department of Biochemistry and Molecular Biology, University College London, U.K.

Biochemical Society Symposium
|September 16, 2000
PubMed
Summary
This summary is machine-generated.

Cyclosporin A (CsA) inhibits the mitochondrial permeability transition pore by binding to cyclophilin D (CyP-D). This interaction reveals the pore

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Simultaneous Measurement of Mitochondrial Calcium and Mitochondrial Membrane Potential in Live Cells by Fluorescent Microscopy
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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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Assessment of Open Probability of the Mitochondrial Permeability Transition Pore in the Setting of Coenzyme Q Excess
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Area of Science:

  • Mitochondrial biophysics and molecular biology
  • Cellular signaling and pore dynamics

Background:

  • The mitochondrial permeability transition pore (mPTP) is a critical regulator of cell death.
  • Cyclosporin A (CsA) is a known inhibitor of the mPTP, but its precise mechanism and structural targets were unclear.

Purpose of the Study:

  • To identify the structural components of the mPTP.
  • To elucidate the mechanism by which CsA inhibits the mPTP.
  • To understand the role of cyclophilin D (CyP-D) in mPTP assembly and function.

Main Methods:

  • Utilized photoactive CsA derivatives for covalent labeling of CyP-D in situ.
  • Employed CyP-D fusion proteins as affinity matrices to identify binding partners.
  • Reconstituted pore activity using protein fractions containing key identified components.

Main Results:

  • Confirmed that CsA inhibits the mPTP by binding to CyP-D.
  • Identified a strong interaction between CyP-D, the voltage-dependent anion channel (VDAC), and adenine nucleotide translocase (ANT).
  • Proposed a model where the mPTP is a complex of VDAC, ANT, and CyP-D at mitochondrial contact sites.
  • Calcium activates the pore via allosteric modulation of pore flicker, not assembly.
  • CsA inhibits pore flicker and reduces calcium binding affinity.

Conclusions:

  • The mPTP is assembled from VDAC, ANT, and CyP-D at mitochondrial contact sites.
  • CyP-D is a central component mediating CsA inhibition and calcium sensitivity.
  • The pore likely represents a stable complex, with calcium regulating its open state.