FTSH PROTEASE 3 facilitates Complex I degradation through a direct interaction with the Complex I subunit PSST

Area of Science:

• Mitochondrial biology
• Protein quality control
• Plant molecular genetics

Background:

• Complex I (CI) is crucial for mitochondrial oxidative phosphorylation and comprises nuclear and mitochondrial subunits.
• CI is susceptible to oxidative damage, necessitating continuous subunit turnover.
• Mechanisms regulating CI abundance and protein quality control are not fully understood.

Purpose of the Study:

• To elucidate the mechanism regulating Complex I abundance in Arabidopsis thaliana.
• To identify the protein interactions involved in CI disassembly and degradation.
• To understand the role of FTSH PROTEASE 3 (FTSH3) in CI protein quality control.

Main Methods:

• Forward genetic screen in an Arabidopsis thaliana CI-deficient mutant.
• Co-immunoprecipitation assays to demonstrate protein-protein interactions.
• Site-directed mutagenesis to identify key amino acid residues and functional domains.

Main Results:

• Identified a novel interaction between the CI Q-module subunit PSST and FTSH3.
• Demonstrated that FTSH3 mediates the disassembly of the CI matrix arm domain for proteolysis.
• Showed that the ATPase function, not proteolytic activity, of FTSH3 is essential for this interaction.

Conclusions:

• FTSH3 recognizes Complex I via the PSST subunit for targeted degradation.
• This interaction is critical for maintaining CI protein quality control.
• The study provides amino acid-level resolution of the FTSH3-CI recognition mechanism.