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A more recent version of this article appeared on November 1, 2004
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Submitted on May 17, 2004
Accepted on August 9, 2004
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*Botanisches Institut, LMU München, 80638 München, Germany;
Department of Biophysics, P. J. Safarik University, 04154 Kosice, Slovak Republik;
ZMBH, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany;
Botanisches Institut der Universität Kiel, 24118 Kiel, Germany
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.