Abstract
The chloroplast inner envelope membrane contains many integral proteins which differ in the number of α-helices that anchor the protein into the bilayer. For most of these proteins it is not known which pathway they engage to reach their final localisation within the membrane. In yeast mitochondria, two distinct sorting/insertion pathways have been described for integral inner membrane proteins, involving the Tim22 and Tim23 translocases. These routes involve on the one hand a conservative sorting, on the other hand a stop-transfer pathway. In this study we performed a systematic characterisation of the import behaviour of seven inner envelope proteins representing different numbers of predicted α-helices. We investigated their energy dependence, import rate, involvement of components of the chloroplast general import pathway and distribution between soluble and membrane fractions. Our results show the existence of at least two different families of inner envelope proteins that can be classified due to the occurrence of an intermediate processing form. Each of the proteins we investigated seems to use a stop-transfer pathway for insertion into the inner envelope.
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Abbreviations
- ATP:
-
Adenosinetriphosphate
- Erv1:
-
Essential for respiration and vegetative growth 1
- HP:
-
Hypothetical protein
- IEP:
-
Inner envelope protein
- Lep:
-
Leader peptidase
- Mia40:
-
Mitochondrial IMS import and assembly protein of 40 kDa
- mOE33:
-
Mature form of the oxygen evolving complex protein of 33 kDa
- PIC1:
-
Permease in chloroplasts 1
- Plsp1:
-
Plastidic signal peptidase type I protease 1
- pOE33:
-
Precursor of the oxygen evolving complex protein of 33 kDa
- PPT:
-
Phosphoenolpyruvate translocator
- pSSU:
-
Precursor of the small subunit of the Ribulosebisphosphatecarboxylase/oxygenase
- Sam:
-
Sorting and assembly machinery
- SSP:
-
Stromal processing peptidase
- Tic:
-
Translocon at the inner envelope of chloroplasts
- Tim4:
-
Translocation intermediate 4
- Tim:
-
Translocase of the inner mitochondrial membrane
- TL:
-
Translation product
- Toc:
-
Translocon at the outer envelope of chloroplasts
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Acknowledgements
We acknowledge funding by the DFG (P. S., J. S. and B. B.) and Bayhost (E. F.-K.) and we thank Prof. Bob Buchanan for critical reading of the manuscript.
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Firlej-Kwoka, E., Strittmatter, P., Soll, J. et al. Import of preproteins into the chloroplast inner envelope membrane. Plant Mol Biol 68, 505–519 (2008). https://doi.org/10.1007/s11103-008-9387-4
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DOI: https://doi.org/10.1007/s11103-008-9387-4