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EMBO reports 7, 12, 1233–1238 (2006)
doi:10.1038/sj.embor.7400828
AOP Published online: 10 November 2006
The Tim21 binding domain connects the preprotein translocases of both mitochondrial membranes
Reinhard Albrecht1, 6, Peter Rehling2, Agnieszka Chacinska2, Jan Brix2, Sergio A Cadamuro3, Rudolf Volkmer4, Bernard Guiard5, Nikolaus Pfanner2 & Kornelius Zeth1, 6
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1 Max-Planck-Institut für Biochemie, Abteilung Membranbiochemie, Am Klopferspitz 18, D-82512 Martinsried, Germany
2 Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Stra e 7, D-79104 Freiburg, Germany
3 Max-Planck-Institut für Biochemie, Laboratory of Bioorganic Chemistry, Am Klopferspitz 18, D-82512 Martinsried, Germany
4 Institut für Medizinische Immunologie, Charité—Universitätsmedizin Berlin, Hessische Strae 3–4, D-10115 Berlin, Germany
5 Centre de Génétique Moléculaire, CNRS, Avenue de la Terrasse—Bât. 26, F-91190 Gif-sur-Yvette, France
6 Max-Planck-Institut für Entwicklungsbiologie, Abteilung Protein Evolution, Spemannstrae 35/I, D-72076 Tübingen, Germany
To whom correspondence should be addressed
Nikolaus Pfanner Tel: +49 761 2035224; Fax: +49 761 2035261; E-mail: nikolaus.pfanner@biochemie.uni-freiburg.de
Kornelius Zeth Tel: +49 7071 601 323; Fax: +49 7071 601 349; E-mail: kornelius.zeth@tuebingen.mpg.de
Received 10 April 2006; Accepted 8 September 2006; Published online 10 November 2006.
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Abstract
Proteins destined for the mitochondrial matrix are imported by the translocase of the outer membrane—the TOM complex—and the presequence translocase of the inner membrane—the TIM23 complex. At present, there is no structural information on components of the presequence translocase. Tim21, a subunit of the presequence translocase consisting of a membrane anchor and a carboxy-terminal domain exposed to the intermembrane space, directly connects the TOM and TIM23 complexes by binding to the intermembrane space domain of the Tom22 receptor. We crystallized the binding domain of Tim21 of Saccharomyces cerevisiae and determined its structure at 1.6 Å resolution. The Tim21 structure represents a new  / -mixed protein fold with two -helices flanked by an extended eight-stranded -sheet. We also identified a core sequence of Tom22 that binds to Tim21. Furthermore, negatively charged amino-acid residues of Tom22 are important for binding to Tim21. Here we suggest a mechanism for the TOM–TIM interaction.
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