Atomic structure of a mitochondrial complex I intermediate from vascular plants.

Area of Science:

• Biochemistry
• Structural Biology
• Plant Science

Background:

• Respiration is vital for cellular energy production in eukaryotes, primarily through the mitochondrial electron transport chain (mETC).
• Complex I (CI) is a crucial entry point for electrons into the mETC, but plant CI structure and assembly are poorly understood due to limited material.
• Understanding plant CI is essential for deciphering energy metabolism and its unique adaptations.

Purpose of the Study:

• To determine the high-resolution cryo-electron microscopy (cryoEM) structure of the Complex I assembly intermediate (CI*) from the plant *Vigna radiata*.
• To elucidate the structural features, subunit composition, and membrane anchoring of plant CI*, including the plant-specific γ-carbonic-anhydrase (γCA) domain.
• To compare plant CI structure with homologous complexes from other organisms and infer differences in assembly and function.

Main Methods:

• Cryo-electron microscopy (cryoEM) was employed to obtain the 3D structure of *Vigna radiata* CI*.
• High-resolution structural analysis was performed to identify core and accessory subunits, including the γCA domain.
• Comparative structural analysis was conducted against known CI structures from yeast, mammals, and bacteria.

Main Results:

• The cryoEM structure of plant CI* was resolved at 3.9 Å resolution, revealing its composition of NADH-binding and CoQ-binding modules, the proximal-pumping module, and the γCA domain.
• Significant structural differences were observed in both core and accessory subunits compared to non-plant CI.
• Detailed insights into the subunit composition and membrane integration of the plant-specific γCA domain were obtained.

Conclusions:

• The structure of plant CI* provides unprecedented detail on the composition and organization of this key mitochondrial complex.
• Observed structural variations suggest distinct assembly pathways and potentially unique physiological roles for plant CI compared to other eukaryotes.
• This study lays the groundwork for further biochemical and functional investigations into plant mitochondrial respiration.