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Related Concept Videos

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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Translocation of Proteins into the Mitochondria01:19

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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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Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

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Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
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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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The Mitochondrial Permeability Transition Pore: Past, Present, and Future.

Michela Carraro1, Christoph Gerle2, Paolo Bernardi1

  • 1Department of Biomedical Sciences, University of Padova, Padova, Italy; email: michela.carraro@unipd.it, paolo.bernardi@unipd.it.

Annual Review of Biophysics
|December 12, 2025
PubMed
Summary

Mitochondrial permeability transition (PT) involves a channel in the inner mitochondrial membrane. Research suggests ATP synthase forms these channels, but not in all species, impacting PT susceptibility.

Keywords:
ATP synthaseadenine nucleotide translocatorchannelscyclophilincyclosporinmitochondrial permeability transition pore

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Area of Science:

  • Mitochondrial physiology and bioenergetics
  • Molecular biology of ion channels
  • Comparative biochemistry

Background:

  • The mitochondrial permeability transition (PT) is a critical event involving increased inner mitochondrial membrane permeability.
  • This process is mediated by the opening of the permeability transition pore (PTP), a high-conductance channel.
  • While the molecular identity of the PTP has been debated, consensus points to specific conformations of FOF1-ATP synthase and the adenine nucleotide translocator.

Purpose of the Study:

  • To investigate the role of ATP synthase in forming channels related to mitochondrial permeability transition.
  • To compare the channel-forming properties of ATP synthases across different species with varying PT susceptibility.
  • To provide a structural framework for understanding the mechanism of channel formation or its absence.

Main Methods:

  • Comparative analysis of ATP synthase structures from various species.
  • Review of existing literature on mitochondrial permeability transition and channel formation.
  • Inferences drawn from structural data to hypothesize about channel mechanisms.

Main Results:

  • ATP synthase forms high-conductance channels in mammals and yeast, associated with PT.
  • ATP synthase in *Artemia franciscana* does not form high-conductance channels and is refractory to PT.
  • ATP synthase in *Drosophila melanogaster* forms low-conductance, Ca2+-selective channels, leading to Ca2+-induced Ca2+ release but not PT.

Conclusions:

  • The channel-forming capacity of ATP synthase varies significantly across species.
  • Species-specific structural differences in ATP synthase likely determine their susceptibility to mitochondrial permeability transition.
  • Structural insights into ATP synthases offer a testable model for future research on PTP mechanisms.