Biogenesis of Tim23 and Tim17, integral components of the TIM machinery for matrix-targeted preproteins

Krisztina Káldi, Matthias F. Bauer, Christian Sirrenberg, Walter Neupert, Michael Brunner

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We analysed the import pathway of Tim23 and of Tim17, components of the mitochondrial import machinery for matrix-targeted preproteins. Tim23 contains two independent import signals. One is located within the first 62 amino acid residues of the hydrophilic domain that, in the assembled protein, is exposed to the intermembrane space. This signal mediates translocation of Tim23 across the outer membrane independently of the membrane potential, ΔΨ. A second import signal is located in the C-terminal membrane-integrated portion of Tim23. It mediates translocation across the outer membrane and insertion into the inner membrane in a strictly ΔΨ-dependent fashion. Structurally, Tim17 is related to Tim23 but lacks a hydrophilic domain. It contains an import signal in the C-terminal half and its import requires ΔΨ. The ΔΨ-dependent import signals of Tim23 and Tim17 are located at corresponding sites in these two homologous proteins. They exhibit features reminiscent of the positively charged N-terminal presequences of matrix-targeted precursors. Import of Tim23 and its insertion into the inner membrane requires Tim22 but not functional Tim23. Thus, biogenesis of the Tim23·17 complex depends on the Tim22 complex, which is the translocase identified as mediating the import of carrier proteins.

Original languageEnglish
Pages (from-to)1569-1576
Number of pages8
JournalEMBO Journal
Issue number6
Publication statusPublished - Mar 16 1998



  • Mitochondrial protein import
  • TIM complex

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)

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