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Plant and Cell Physiology Advance Access originally published online on November 10, 2008
Plant and Cell Physiology 2008 49(12):1917-1921; doi:10.1093/pcp/pcn171
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Short Communication

pH Sensitivity of the GTPase Toc33 as a Regulatory Circuit for Protein Translocation into Chloroplasts

Tihana Bionda1,3, Patrick Koenig2,3, Mislav Oreb1, Ivo Tews2 and Enrico Schleiff1,*

1JWGU Frankfurt am Main, Cluster of Excellence Macromolecular Complexes, Center of Membrane Proteomics, Department of Biosciences, Molecular Cell Biology, Max-von-Laue Str. 9, D-60439 Frankfurt, Germany
2Heidelberg University Biochemistry Centre, Im Neuenheimer Feld 328, D-69120 Heidelberg, Germany

*Corresponding author: E-mail, schleiff{at}bio.uni-frankfurt.de; Fax, +49-69-798-29286.


  Abstract

The properties of membrane-embedded GTPases are investigated to understand translocation of preprotein across the outer envelope of chloroplasts. The homo- and heterodimerization events of the GTPases had been established previously. We show that the hydrolytic activity of the GTPase Toc33 is pH insensitive in the homodimeric conformation but has a bell-shaped pH optimum in the monomeric conformation. Further, Toc33 GTPase homodimerization and protein translocation into chloroplasts are pH sensitive as well. pH sensitivity might serve to regulate translocation; alternatively, the documented pH sensitivity might reflect a mechanistic requirement for GTPase silencing during translocation as the GTPase switches between homo- and heterodimeric conformations.

Keywords: Arabidopsis thaliana and Pisum sativum - Dimerization - GTPase - pH sensitivity - Protein translocation - TOC

Abbreviations: pSSU, precursor of the small subunit of Rubisco; Toc, translocon at the outer envelope of chloroplasts; Toc33N, soluble GTPase domain of Toc33

3These authors contributed equally to this work.

(Received October 20, 2008; Accepted October 31, 2008)
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