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  • Structural snapshot of the ...
    Araiso, Yuhei; Imai, Kenichiro; Endo, Toshiya

    The FEBS journal, September 2021, Letnik: 288, Številka: 18
    Journal Article

    The translocase of the outer mitochondrial membrane (TOM) complex is the main entry gate for most mitochondrial proteins. The TOM complex is a multisubunit membrane protein complex consisting of a β‐barrel protein Tom40 and six α‐helical transmembrane (TM) proteins, receptor subunits Tom20, Tom22, and Tom70, and regulatory subunits Tom5, Tom6, and Tom7. Although nearly 30 years have passed since the main components of the TOM complex were identified and characterized, the structural details of the TOM complex remained poorly understood until recently. Thanks to the rapid development of the cryoelectron microscopy (EM) technology, high‐resolution structures of the yeast TOM complex have become available. The identified structures showed a symmetric dimer containing five different subunits including Tom22. Biochemical and mutational analyses based on the TOM complex structure revealed the presence of different translocation paths within the Tom40 import channel for different classes of translocating precursor proteins. Previous studies including our cross‐linking analyses indicated that the TOM complex in intact mitochondria is present as a mixture of the trimeric complex containing Tom22. Furthermore, the dimeric complex lacking Tom22, and the trimer and dimer may handle different sets of mitochondrial precursor proteins for translocation across the outer membrane. In this Structural Snapshot, we will discuss possible rearrangement of the subunit interactions upon dynamic conversion of the TOM complex between the different subunit assembly states, the Tom22‐containing core dimer and trimer. The cryoelectron microscopy structures of the mitochondrial protein import gate, the translocase of the outer mitochondrial membrane (TOM) complex, have become available. The yeast TOM complex structure shows the presence of two paths within the import channel for different classes of mitochondrial precursor proteins. This explains how the TOM import channel can handle and translocate ˜ 1000 different precursor proteins with different physical and chemical properties from the cytosol to the mitochondrial interior across the outer membrane.