In-cell architecture of the mitochondrial respiratory chain

Area of Science:

• Mitochondrial biology
• Structural biology
• Cellular respiration

Background:

• Mitochondria generate cellular energy (ATP) via oxidative phosphorylation.
• The respiratory chain complexes' native organization within mitochondria is not fully understood.
• Understanding this organization is key to comprehending cellular energy production.

Purpose of the Study:

• To visualize the native structures and organization of mitochondrial respiratory complexes in *Chlamydomonas reinhardtii* cells.
• To determine the high-resolution structure of the respirasome supercomplex.
• To model the arrangement of respiratory complexes within native mitochondria.

Main Methods:

• In situ cryo-electron tomography (cryo-ET) to visualize native mitochondrial complexes.
• Single-particle cryo-electron microscopy (cryo-EM) for high-resolution structure determination.
• Computational modeling to integrate structural data and propose organizational models.

Main Results:

• Mitochondrial ATP synthases and respiratory complexes segregate into distinct membrane domains (curved vs. flat cristae).
• Respiratory complexes I, III, and IV were observed to assemble into a respirasome supercomplex.
• A 5-angstrom (Å) resolution structure of the respirasome was determined, showing the binding site for electron carrier cytochrome c.
• A 2.4-Å resolution structure was obtained for key components.

Conclusions:

• The native mitochondrial inner membrane exhibits domain-specific organization of energy-producing complexes.
• The respirasome supercomplex is a key functional unit, facilitating efficient electron transfer.
• This study provides a structural basis for understanding respiratory chain organization and function in native mitochondria.