Mapping protein interactions in the active TOM-TIM23 supercomplex.

Area of Science:

• Mitochondrial protein import
• Molecular cell biology
• Membrane transport

Background:

• Nuclear-encoded mitochondrial proteins require translocation across the outer and inner mitochondrial membranes.
• The TOM (translocase of the outer membrane) and TIM23 (translocase of the inner membrane) complexes mediate matrix protein import.
• The precise organization and function of the TOM-TIM23 transition zone remain poorly understood.

Purpose of the Study:

• To investigate the molecular organization of the TOM-TIM23 transition zone.
• To elucidate the mechanism of precursor protein transfer between TOM and TIM23 complexes.
• To map the interactions at the intermembrane space (IMS) interface during mitochondrial protein transport.

Main Methods:

• Design of a stalled translocation intermediate precursor protein.
• Chemical cross-linking coupled with mass spectrometry (MS).
• Structural modeling and computational analysis.

Main Results:

• Visualized the molecular environment at the TOM-TIM23 intermembrane space interface.
• Mapped interactions between the import motor and the translocating precursor.
• Provided high-resolution insights into the presequence handover mechanism.

Conclusions:

• Established a framework for understanding protein transfer between TOM and TIM23.
• Detailed the molecular basis of precursor recognition and translocation across mitochondrial membranes.
• Advanced the understanding of mitochondrial protein import pathways.