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Molecular and Cellular Biology, November 2003, p. 7818-7828, Vol. 23, No. 21
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.21.7818-7828.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Mitochondria Use Different Mechanisms for Transport of Multispanning Membrane Proteins through the Intermembrane Space

Ann E. Frazier,1,2 Agnieszka Chacinska,1 Kaye N. Truscott,1 Bernard Guiard,3 Nikolaus Pfanner,1* and Peter Rehling1

Institut für Biochemie und Molekularbiologie,1 Fakultät für Biologie, Universität Freiburg, D-79104 Freiburg, Germany,2 Centre de Génétique Moléculaire, Laboratoire Propre du CNRS, Université Pierre et Marie Curie, 91190 Gif-sur-Yvette, France3

Received 31 March 2003/ Returned for modification 11 June 2003/ Accepted 31 July 2003

The mitochondrial inner membrane contains numerous multispanning integral proteins. The precursors of these hydrophobic proteins are synthesized in the cytosol and therefore have to cross the mitochondrial outer membrane and intermembrane space to reach the inner membrane. While the import pathways of noncleavable multispanning proteins, such as the metabolite carriers, have been characterized in detail by the generation of translocation intermediates, little is known about the mechanism by which cleavable preproteins of multispanning proteins, such as Oxa1, are transferred from the outer membrane to the inner membrane. We have identified a translocation intermediate of the Oxa1 preprotein in the translocase of the outer membrane (TOM) and found that there are differences from the import mechanisms of carrier proteins. The intermembrane space domain of the receptor Tom22 supports the stabilization of the Oxa1 intermediate. Transfer of the Oxa1 preprotein to the inner membrane is not affected by inactivation of the soluble TIM complexes. Both the inner membrane potential and matrix heat shock protein 70 are essential to release the preprotein from the TOM complex, suggesting a close functional cooperation of the TOM complex and the presequence translocase of the inner membrane. We conclude that mitochondria employ different mechanisms for translocation of multispanning proteins across the aqueous intermembrane space.

* Corresponding author. Mailing address: Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany. Phone: 49-761 203 5224. Fax: 49-761 203 5261. E-mail: Nikolaus.Pfanner{at}biochemie.uni-freiburg.de.

Molecular and Cellular Biology, November 2003, p. 7818-7828, Vol. 23, No. 21
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.21.7818-7828.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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