Structural basis for a complex I mutation that blocks pathological ROS production.

Area of Science:

• Biochemistry
• Cardiovascular Biology
• Mitochondrial Medicine

Background:

• Mitochondrial complex I is implicated in cardiac ischemia-reperfusion (IR) injury via reactive oxygen species (ROS) production.
• A specific point mutation (P25L) in the ND6 subunit of complex I alters its structure and function.

Purpose of the Study:

• To investigate the structural and functional consequences of the ND6-P25L mutation in mitochondrial complex I.
• To determine the role of reverse electron transfer (RET)-mediated ROS production in cardiac IR injury.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of the mutant complex I.
• Biochemical assays to assess NADH oxidation and ROS production.
• In vivo studies using ND6-P25L mice subjected to cardiac IR injury.

Main Results:

• The ND6-P25L mutation causes subtle structural changes in complex I, promoting a rapid transition to the 'deactive' state.
• Mutant complex I remains fully active for NADH oxidation but cannot produce ROS via RET.
• ND6-P25L mice exhibit normal mitochondrial function but are protected against cardiac IR injury due to the absence of RET ROS.

Conclusions:

• A single point mutation in mitochondrial complex I that abolishes RET ROS production protects against cardiac IR injury.
• This highlights the pathological role of RET-derived ROS in IR injury.
• Targeting RET in complex I may offer a therapeutic strategy for cardiac protection.