Journal Article

Phosphorylation regulates the assembly of chloroplast import machinery

Mislav Oreb, Anja Höfle, Oliver Mirus and Enrico Schleiff

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 59, issue 9, pages 2309-2316
Published in print June 2008 | ISSN: 0022-0957
Published online May 2008 | e-ISSN: 1460-2431 | DOI:

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Chloroplast function depends on the translocation of cytosolically synthesized precursor proteins into the organelle. The recognition and transfer of most precursor proteins across the outer membrane depend on a membrane inserted complex. Two receptor components of this complex, Toc34 and Toc159, are GTPases, which can be phosphorylated by kinases present in the hosting membrane. However, the physiological function of phosphorylation is not yet understood in detail. It is demonstrated that both receptors are phosphorylated within their G-domains. In vitro, the phosphorylation of Toc34 disrupts both homo- and heterodimerization of the G-domains as determined using a phospho-mimicking mutant. In endogenous membranes this mutation or phosphorylation of the wild-type receptor disturbs the association of Toc34, but not of Toc159 with the translocation pore. Therefore, phosphorylation serves as an inhibitor for the association of Toc34 with other components of the complex and phosphorylation can now be discussed as a mechanism to exchange different isoforms of Toc34 within this ensemble.

Keywords: GTPase; membrane complex dynamics; phosphorylation; plastids; protein complex assembly; protein translocation; TOC

Journal Article.  4749 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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