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  • The EMBO Journal (2003) 22, 5370 - 5381
  • doi:10.1093/emboj/cdg532

Mitochondrial translocation contact sites: separation of dynamic and stabilizing elements in formation of a TOM–TIM–preprotein supercomplex

Agnieszka Chacinska1, Peter Rehling1, Bernard Guiard2, Ann E. Frazier1,3, Agnes Schulze-Specking1, Nikolaus Pfanner1, Wolfgang Voos1 and Chris Meisinger1

  1. Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
  2. Centre de Génétique Moléculaire, Laboratoire propre du CNRS associeté à l'Université Pierre et Marie Curie, 91190 Gif-sur-Yvette, France
  3. Fakultät für Biologie, Universität Freiburg, D-79104 Freiburg, Germany

Correspondence to:

Nikolaus Pfanner, E-mail: Nikolaus.Pfanner@biochemie.uni-freiburg.de

Received 15 May 2003; Accepted 22 August 2003; Revised 4 August 2003

Preproteins with N-terminal presequences are imported into mitochondria at translocation contact sites that include the translocase of the outer membrane (TOM complex) and the presequence translocase of the inner membrane (TIM23 complex). Little is known about the functional cooperation of these translocases. We have characterized translocation contact sites by a productive TOM–TIM–preprotein supercomplex to address the role of three translocase subunits that expose domains to the intermembrane space (IMS). The IMS domain of the receptor Tom22 is required for stabilization of the translocation contact site supercomplex. Surprisingly, the N-terminal segment of the channel Tim23, which tethers the TIM23 complex to the outer membrane, is dispensable for both protein import and generation of the TOM–TIM supercomplex. Tim50, with its large IMS domain, is crucial for generation but not for stabilization of the supercomplex. Thus, Tim50 functions as a dynamic factor and the IMS domain of Tom22 represents a stabilizing element in formation of a productive translocation contact site supercomplex.

  • Keywords:

    • contact sites,
    • mitochondria,
    • protein translocation,
    • Saccharomyces cerevisiae