High-Resolution Visualization of Supramolecular Structures of ATP Synthase and Respiratory Supercomplexes in the Mitochondrial Membrane
By using cryo-electron microscopy on sub-mitochondrial particles, researchers successfully analyzed mitochondrial inner membrane proteins in their native state. The study identified ATP synthase tetramers and novel configurations of respiratory supercomplexes, paving the way for advanced disease-related mitochondrial research.
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- 📰 Published: April 14, 2026 at 19:47
- 🔍 Collected: April 14, 2026 at 11:31
- 🤖 AI Analyzed: April 19, 2026 at 17:24 (125h 52m after Collected)
## Published Paper
"Structures of respiratory supercomplexes and ATP synthase oligomers in mammalian mitochondrial inner membrane"
## Overview
In this study, using sub-mitochondrial particles prepared from bovine heart mitochondria, we conducted a structural analysis of mitochondrial inner membrane proteins in their native, intact membrane state via single-particle analysis using cryo-electron microscopy.
As a result, we clearly demonstrated for the first time that ATP synthase (FoF1) exists as a dimer connected by IF1 proteins, and that these further associate into tetrameric structures that actually exist within the mitochondrial inner membrane. This tetramer strongly bends the membrane and is considered to play a critical role in the formation of mitochondrial cristae. Furthermore, the conventional hypothesis that stable lipids exist at the center of the ATP synthase's rotating ring was not supported. In addition, regarding the respiratory chain supercomplexes, we identified the existence of a novel configuration, CI1CIII2CIV3, as well as a giant mega-complex consisting of CI2CIII2CIV6, in addition to previously known configurations, revealing that respiratory chain complexes exist in the membrane in diverse combinations.
This achievement demonstrates the effectiveness of a new method capable of direct structural analysis of mitochondrial membrane proteins in their native state from small sample amounts. It is expected to lead to applications in disease-related mitochondrial research, structural analysis using patient biopsy samples, and a paradigm shift in membrane protein structural research.
## Background
Mitochondria are the "energy factories" that synthesize ATP (adenosine triphosphate) within cells and are also the production sites for essential substances for life activities such as amino acids and lipids. The inner mitochondrial membrane is densely populated with ATP synthase (FoF1), responsible for ATP synthesis, and respiratory chain complexes (Complexes I-IV), responsible for electron transport. It has been thought that these membrane proteins assemble to form supramolecular complexes, contributing to the efficiency of energy production.
However, in many structural studies to date, samples were used in which membrane proteins were extracted from the membrane using detergents, and the actual arrangement and assembly state (native structure) within the biological membrane were not fully understood.
Figure 1. While the current method obtains the structure of the membrane protein in its original state on the biological membrane, the conventional method through a purification process using detergents may result in the loss of the membrane protein's original structural state or the generation of artificial dimeric structures.
## Research Results
Determining the native structure of membrane proteins on SMP (Figure 1)
Conventionally, the structural determination of membrane proteins has been performed by solubilizing the biological membrane with detergents and then purifying the obtained membrane proteins via chromatography. This method requires a large amount of sample and immense effort, and there was a possibility that the original association state of membrane proteins and their interactions with other factors would be lost during the solubilization and purification processes.
Therefore, in this study, we conducted single-particle analysis by cryo-electron microscopy using sub-mitochondrial particles (SMP) prepared from bovine heart mitochondria. By analyzing while retaining the membrane structure, we succeeded in structurally analyzing mitochondrial inner membrane proteins in a native state without disrupting the membrane. As a result, we were able to determine the native structures of ATP synthase FoF1 and respiratory chain complexes.
Proving the existence of higher-order structures of ATP synthase (Figure 2)
It was confirmed that ATP synthase (FoF1) exists as a dimer connected by a rod-like protein called IF1. Furthermore, we clearly demonstrated that a tetrameric structure, in which these dimers associate, actually exists within the mitochondrial inner membrane. This tetrameric structure has the characteristic of strongly bending the membrane and is thought to play an important role in the formation of cristae, which are fold structures unique to the inner mitochondrial membrane. Previously, the possibility was pointed out that the FoF1 tetramer connected by IF1 was an artificial structure generated during the purification process, but this study demonstrated that it is a structure that actually exists in vivo. We also tested the hypothesis that lipids are bound to the center of the intramembrane rotor part (c-ring) of ATP synthase, but we did not obtain structural evidence to support the presence of stable lipids. It was shown that the structure previously thought to be lipids is highly likely to be detergent that entered the ring during the purification process.
"Structures of respiratory supercomplexes and ATP synthase oligomers in mammalian mitochondrial inner membrane"
## Overview
In this study, using sub-mitochondrial particles prepared from bovine heart mitochondria, we conducted a structural analysis of mitochondrial inner membrane proteins in their native, intact membrane state via single-particle analysis using cryo-electron microscopy.
As a result, we clearly demonstrated for the first time that ATP synthase (FoF1) exists as a dimer connected by IF1 proteins, and that these further associate into tetrameric structures that actually exist within the mitochondrial inner membrane. This tetramer strongly bends the membrane and is considered to play a critical role in the formation of mitochondrial cristae. Furthermore, the conventional hypothesis that stable lipids exist at the center of the ATP synthase's rotating ring was not supported. In addition, regarding the respiratory chain supercomplexes, we identified the existence of a novel configuration, CI1CIII2CIV3, as well as a giant mega-complex consisting of CI2CIII2CIV6, in addition to previously known configurations, revealing that respiratory chain complexes exist in the membrane in diverse combinations.
This achievement demonstrates the effectiveness of a new method capable of direct structural analysis of mitochondrial membrane proteins in their native state from small sample amounts. It is expected to lead to applications in disease-related mitochondrial research, structural analysis using patient biopsy samples, and a paradigm shift in membrane protein structural research.
## Background
Mitochondria are the "energy factories" that synthesize ATP (adenosine triphosphate) within cells and are also the production sites for essential substances for life activities such as amino acids and lipids. The inner mitochondrial membrane is densely populated with ATP synthase (FoF1), responsible for ATP synthesis, and respiratory chain complexes (Complexes I-IV), responsible for electron transport. It has been thought that these membrane proteins assemble to form supramolecular complexes, contributing to the efficiency of energy production.
However, in many structural studies to date, samples were used in which membrane proteins were extracted from the membrane using detergents, and the actual arrangement and assembly state (native structure) within the biological membrane were not fully understood.
Figure 1. While the current method obtains the structure of the membrane protein in its original state on the biological membrane, the conventional method through a purification process using detergents may result in the loss of the membrane protein's original structural state or the generation of artificial dimeric structures.
## Research Results
Determining the native structure of membrane proteins on SMP (Figure 1)
Conventionally, the structural determination of membrane proteins has been performed by solubilizing the biological membrane with detergents and then purifying the obtained membrane proteins via chromatography. This method requires a large amount of sample and immense effort, and there was a possibility that the original association state of membrane proteins and their interactions with other factors would be lost during the solubilization and purification processes.
Therefore, in this study, we conducted single-particle analysis by cryo-electron microscopy using sub-mitochondrial particles (SMP) prepared from bovine heart mitochondria. By analyzing while retaining the membrane structure, we succeeded in structurally analyzing mitochondrial inner membrane proteins in a native state without disrupting the membrane. As a result, we were able to determine the native structures of ATP synthase FoF1 and respiratory chain complexes.
Proving the existence of higher-order structures of ATP synthase (Figure 2)
It was confirmed that ATP synthase (FoF1) exists as a dimer connected by a rod-like protein called IF1. Furthermore, we clearly demonstrated that a tetrameric structure, in which these dimers associate, actually exists within the mitochondrial inner membrane. This tetrameric structure has the characteristic of strongly bending the membrane and is thought to play an important role in the formation of cristae, which are fold structures unique to the inner mitochondrial membrane. Previously, the possibility was pointed out that the FoF1 tetramer connected by IF1 was an artificial structure generated during the purification process, but this study demonstrated that it is a structure that actually exists in vivo. We also tested the hypothesis that lipids are bound to the center of the intramembrane rotor part (c-ring) of ATP synthase, but we did not obtain structural evidence to support the presence of stable lipids. It was shown that the structure previously thought to be lipids is highly likely to be detergent that entered the ring during the purification process.