Plant Molecular Biology

, 77:381 | Cite as

The localization of Tic20 proteins in Arabidopsis thaliana is not restricted to the inner envelope membrane of chloroplasts

  • Anu B. Machettira
  • Lucia E. Gross
  • Maik S. Sommer
  • Benjamin L. Weis
  • Gisela Englich
  • Joanna TrippEmail author
  • Enrico SchleiffEmail author


Tic20 is a central, membrane-embedded component of the precursor protein translocon of the inner envelope of chloroplasts (TIC). In Arabidopsis thaliana, four different isoforms of Tic20 exist. They are annotated as atTic20-I, -II, -IV and -V and form two distinct phylogenetic subfamilies in embryophyta. Consistent with atTic20-I being the only essential isoform for chloroplast development, we show that the protein is exclusively targeted to the chloroplasts inner envelope. The same result is observed for atTic20-II. In contrast, atTic20-V is localized in thylakoids and atTic20-IV dually localizes to chloroplasts and mitochondria. These results together with the previously established expression profiles explain the recently described phenotypes of Tic20 knockout plants and point towards a functional diversification of these proteins within the family. For all Tic20 proteins a 4-helix topology is proposed irrespective of the targeted membrane, which in part could be confirmed in vivo by application of a self-assembling GFP-based topology approach. By the same approach we show that the inner envelope localized Tic20 proteins expose their C-termini to the chloroplast stroma. This localization would be consistent with the positive inside rule considering a stromal translocation intermediate as discussed.


Tic20 Chloroplast protein import Membrane protein topology 



The work was supported by grants from Deutsche Forschungsgemeinschaft (SFB807-P17), the Center of Membrane Proteomics Frankfurt (CMP), the Cluster of Excellence “Macromolecular Complexes” and Volkswagenstiftung to E.S. and from the Deutsche Forschungsgemeinschaft (TR985/1-1) to J.T. The authors would like to thank Oliver Mirus for bioinformatic support.


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Anu B. Machettira
    • 2
  • Lucia E. Gross
    • 2
  • Maik S. Sommer
    • 2
  • Benjamin L. Weis
    • 2
  • Gisela Englich
    • 2
  • Joanna Tripp
    • 2
    Email author
  • Enrico Schleiff
    • 1
    • 2
    Email author
  1. 1.Department of Biosciences, Cluster of Excellence ‘Macromolecular Complexes, Center of Membrane ProteomicsJohann-Wolfgang-Goethe University FrankfurtFrankfurt am MainGermany
  2. 2.Department of Biosciences, Molecular Cell Biology of PlantsJohann-Wolfgang-Goethe University FrankfurtFrankfurt am MainGermany

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