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Molecular and Cellular Biology, September 1998, p. 5256-5262, Vol. 18, No. 9
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Dynamics of the TOM Complex of Mitochondria during Binding and Translocation of Preproteins

Doron Rapaport,1 Klaus-Peter Künkele,1 Markus Dembowski,1 Uwe Ahting,1 Frank E. Nargang,2 Walter Neupert,1 and Roland Lill3,*

Institut für Physiologische Chemie, Physikalische Biochemie und Zellbiologie der Universität München, 80336 Munich,1 and Institut für Zytobiologie der Philipps-Universität Marburg, 35033 Marburg,3 Germany, and Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E92

Received 13 February 1998/Returned for modification 30 March 1998/Accepted 26 June 1998

Translocation of preproteins across the mitochondrial outer membrane is mediated by the TOM complex. This complex consists of receptor components for the initial contact with preproteins at the mitochondrial surface and membrane-embedded proteins which promote transport and form the translocation pore. In order to understand the interplay between the translocating preprotein and the constituents of the TOM complex, we analyzed the dynamics of the TOM complex of Neurospora crassa and Saccharomyces cerevisiae mitochondria by following the structural alterations of the essential pore component Tom40 during the translocation of preproteins. Tom40 exists in a homo-oligomeric assembly and dynamically interacts with Tom6. The Tom40 assembly is influenced by a block of negatively charged amino acid residues in the cytosolic domain of Tom22, indicating a cross-talk between preprotein receptors and the translocation pore. Preprotein binding to specific sites on either side of the outer membrane (cis and trans sites) induces distinct structural alterations of Tom40. To a large extent, these changes are mediated by interaction with the mitochondrial targeting sequence. We propose that such targeting sequence-induced adaptations are a critical feature of translocases in order to facilitate the movement of preproteins across cellular membranes.

* Corresponding author. Mailing address: Institut für Zytobiologie der Philipps-Universität Marburg, Robert-Koch-Str. 5, 35033 Marburg, Germany. Phone: 49-6421-28 6449. Fax: 49-6421-28 6414. E-mail: Lill{at}mailer.uni-marburg.de.

Molecular and Cellular Biology, September 1998, p. 5256-5262, Vol. 18, No. 9
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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