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Vol. 15, Issue 11, 5130-5144, November 2004

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Toc12, a Novel Subunit of the Intermembrane Space Preprotein Translocon of Chloroplasts

Thomas Becker ^*, Jozef Hritz , Markus Vogel , Alexander Caliebe  ^||, Bernd Bukau , Jürgen Soll ^*, and Enrico Schleiff ^* ¶

^* Botanisches Institut, LMU München, 80638 München, Germany; Department of Biophysics, P. J. Safarik University, 04154 Kosice, Slovak Republik; Zentrum für Molekulare Biologie der Universität Heidelberg, 69120 Heidelberg, Germany; and Botanisches Institut der Universität Kiel, 24118 Kiel, Germany

Submitted May 17, 2004; Accepted August 9, 2004
Monitoring Editor: Thomas Fox

Translocation of proteins across membranes is essential for the biogenesis of each cell and is achieved by proteinaceous complexes. We analyzed the translocation complex of the intermembrane space from chloroplasts and identified a 12-kDa protein associated with the Toc machinery. Toc12 is an outer envelope protein exposing a soluble domain into the intermembrane space. Toc12 contains a J-domain and stimulates the ATPase activity of DnaK. The conformational stability and the ability to stimulate Hsp70 are dependent on a disulfide bridge within the loop region of the J-domain, suggesting a redox-regulated activation of the chaperone. Toc12 is associated with Toc64 and Tic22. Its J-domain recruits the Hsp70 of outer envelope membrane to the intermembrane space translocon and facilitates its interaction to the preprotein.

^|| Present address: Strathmann AG Hamburg, Sellhopsweg 1, 22459 Hamburg, Germany.

^¶ Corresponding author. E-mail address: schleiff{at}botanik.biologie.unimuenchen.de.

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