Structural basis for energy transduction by respiratory alternative complex III.

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Electron transfer in respiratory chains is crucial for cellular energy production.
• Prokaryotes utilize diverse electron donors/acceptors and possess alternative respiratory complexes.
• Alternative complex III (ACIII) is a quinol:cytochrome c/HiPIP oxidoreductase found in some prokaryotes.

Purpose of the Study:

• To determine the high-resolution structure of ACIII from Rhodothermus marinus.
• To understand the catalytic mechanism and energy transduction of ACIII.
• To identify key structural features, including cofactor arrangement and proton pathways.

Main Methods:

• Single-particle cryo-electron microscopy (cryo-EM) was employed.
• The structure of ACIII was determined at 3.9 Å resolution.
• Structural analysis focused on cofactor positioning and membrane-associated features.

Main Results:

• A unique structure of ACIII was resolved.
• The arrangement of four iron-sulfur clusters and six c-type hemes was established.
• A putative quinol-binding site and two proton pathways within the membrane were identified.

Conclusions:

• The determined ACIII structure provides critical insights into its catalytic mechanism.
• ACIII functions as a redox-driven proton pump, contributing to cellular energy transduction.
• This study advances the understanding of prokaryotic respiratory chains and energy conservation.