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Nat Struct Biol. 2001 Dec;8(12):1074-82.

A presequence- and voltage-sensitive channel of the mitochondrial preprotein translocase formed by Tim23.

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Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany.


Proteins imported into the mitochondrial matrix are synthesized in the cytosol with an N-terminal presequence and are translocated through hetero-oligomeric translocase complexes of the outer and inner mitochondrial membranes. The channel across the inner membrane is formed by the presequence translocase, which consists of roughly six distinct subunits; however, it is not known which subunits actually form the channel. Here we report that purified Tim23 forms a hydrophilic, approximately 13-24 A wide channel characteristic of the mitochondrial presequence translocase. The Tim23 channel is cation selective and activated by a membrane potential and presequences. The channel is formed by the C-terminal domain of Tim23 alone, whereas the N-terminal domain is required for selectivity and a high-affinity presequence interaction. Thus, Tim23 forms a voltage-sensitive high-conductance channel with specificity for mitochondrial presequences.

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