Tom40 forms the hydrophilic channel of the mitochondrial import pore for preproteins

Kerstin Hill, Kirstin Model, Michael T. Ryan, Klaus Dietmeier, Falk Martint, Richard Wagner, Nikolaus Pfanner

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The mitochondrial outer membrane contains machinery for the import of preproteins encoded by nuclear genes. Eight different Tom (translocase of outer membrane) proteins have been identified that function as receptors and/or are related to a hypothetical general import pore. Many mitochondrial membrane channel activities have been described, including one related to Tim23 of the inner-membrane protein-import system; however, the pore-forming subunit(s) of the Tom machinery have not been identified until now. Here we describe the expression and functional reconstitution of Tom40, an integral membrane protein with mainly β-sheet structure. Tom40 forms a cation- selective high-conductance channel that specifically binds to and transports mitochondrial-targeting sequences added to the cis side of the membrane. We conclude that Tom40 is the pore-forming subunit of the mitochondrial general import pore and that it constitutes a hydrophilic, ~22 Å wide channel for the import of preproteins.

Original languageEnglish
Pages (from-to)516-521
Number of pages6
Issue number6701
Publication statusPublished - 1 Oct 1998
Externally publishedYes

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