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Structural basis of mitochondrial membrane bending by the I-II-III2-IV2 supercomplex.

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A newly discovered respiratory supercomplex in ciliates shapes mitochondrial membranes. This large assembly of proteins and lipids induces membrane curvature, enabling specialized energy conversion.

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Area of Science:

  • Cell Biology
  • Biochemistry
  • Structural Biology

Background:

  • Mitochondrial energy conversion relies on the complex structure of the inner mitochondrial membrane.
  • The precise organization of respiratory chain components is crucial for efficient function.

Purpose of the Study:

  • To investigate the structure and function of a respiratory supercomplex in ciliates.
  • To understand how this supercomplex influences mitochondrial membrane architecture.

Main Methods:

  • Cryo-electron microscopy and cryo-tomography were used to determine the structure of the supercomplex.
  • Molecular dynamics simulations were employed to analyze the supercomplex's effect on membrane curvature.

Main Results:

  • A stable 5.8-MDa supercomplex (I-II-III2-IV2) comprising 150 proteins and 311 lipids was characterized.
  • The supercomplex formation leads to a wedge-shaped gap and tilted associations, inducing significant membrane curvature.
  • Molecular dynamics simulations confirmed the supercomplex actively drives membrane tubulation of cristae.

Conclusions:

  • The identified respiratory supercomplex actively shapes the inner mitochondrial membrane through protein subunit evolution.
  • This structural specialization enables functional adaptation in mitochondrial energy conversion in ciliates.