Content
Import of preproteins into the chloroplast inner envelope membran
14.08.2008
The chloroplast inner envelope membrane contains many integral proteins which differ in the number of a-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 a-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.
