Structural basis for the mechanism of respiratory complex I

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Complex I is vital for cellular energy production, linking electron transfer to proton translocation.
• Its dysfunction is linked to neurodegenerative diseases and aging due to reactive oxygen species (ROS) production.
• The precise mechanism of Complex I remains largely unknown.

Purpose of the Study:

• To elucidate the mechanism of Complex I by determining its structure.
• To understand the role of NADH interaction and electron transfer in enzyme function.
• To investigate the origins of ROS production and implications for disease.

Main Methods:

• Determined X-ray crystal structures of the oxidized and reduced hydrophilic domain of Thermus thermophilus Complex I.
• Analyzed structures at up to 3.1 A resolution to identify molecular interactions and conformational changes.
• Identified bound metals and unique cysteine coordination motifs.

Main Results:

• Revealed the mode of NADH interaction, explaining kinetic data and informing ROS production mechanisms.
• Identified potential iron-binding sites in the Nqo15 subunit interface.
• Observed conformational changes upon reduction, including adjustments in the nucleotide-binding pocket and shifts in alpha-helices, driven by iron-sulfur cluster reduction.
• Discovered an unprecedented 'on/off switch' in tandem cysteine coordination to the N2 cluster upon reduction.

Conclusions:

• Proposed a novel mechanism for coupling electron transfer and proton translocation in Complex I.
• This mechanism involves conformational changes and protonation/deprotonation events mediated by tandem cysteines.
• Structural insights provide a basis for understanding Complex I dysfunction in disease and aging.