TOM-TIM23 supercomplex formation

Abstract

Mitochondria import the vast majority of proteins from the cytosol. Protein translocation machineries in outer and inner membranes facilitate precursor recognition and transport. Most mitochondrial proteins utilize N-terminal presequences as targeting signals that eventually direct them across the inner mitochondrial membrane. These precursors are transported by the TOM complex across the outer-, and subsequently by the TIM23 complex across the inner membrane. During this process the translocases align and the polypeptide chain is translocated across both membranes in a coupled manner. A transient precursor-containing TOM-TIM23 supercomplex is formed. This TOM-TIM23 supercomplex provides a fascinating import intermediate which can be stabilized if the precursor contains a tightly folded moiety at the C-terminus that is not able to pass through the TOM complex. Such a supercomplex can be generated during in vitro import, and in vivo. The stabilized TOM-TIM23 supercomplex can be purified for downstream analysis. The possibility of pausing translocation at this step provides a means to understand the mechanisms underlying precursor translocation.

Keywords: Import; Mitochondria; Supercomplex; TIM23; TOM.