Import of nuclear-encoded precursor proteins into mitochondria and their subsequent sorting into mitochondrial subcompartments is mediated by translocase enzymes in the mitochondrial outer and inner membranes. Precursor proteins carrying amino-terminal targeting signals are translocated into the matrix by the integral inner membrane proteins Tim23 and Tim17 in cooperation with Tim44 and mitochondrial Hsp70. We describe here the discovery of a new pathway for the transport of members of the mitochondrial carrier family and other inner membrane proteins that contain internal targeting signals. Two related proteins in the intermembrane space, Tim10/Mrs11 and Tim12/Mrs5, interact sequentially with these precursors and facilitate their translocation across the outer membrane, irrespective of the membrane potential. Tim10 and Tim12 are found in a complex with Tim22, which takes over the precursor and mediates its membrane-potential-dependent insertion into the inner membrane. This interaction of Tim10 and Tim12 with the precursors depends on the presence of divalent metal ions. Both proteins contain a zinc-finger-like motif with four cysteines and bind equimolar amounts of zinc ions.

• PMID: 9495346
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Journal Article | Research Support, Non-U.S. Gov't

Authors

Sirrenberg C, Endres M, Fölsch H, Stuart RA, Neupert W, Brunner M

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