title: Import of preproteins into the chloroplast inner envelope membrane.
abstract: The chloroplast inner envelope membrane contains many integral proteins which differ in the number of alpha-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 alpha-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.
authors.affiliation: Department Biology I, Plant Biochemistry, Ludwig-Maximilians-Universität München, Grosshadernerstr. 2-4, 82152 Planegg-Martinsried, Germany.
authors.forename: Ewa
authors.initials: E
authors.lastname: Firlej-Kwoka
authors.forename: Penelope
authors.initials: P
authors.lastname: Strittmatter
authors.forename: Jürgen
authors.initials: J
authors.lastname: Soll
authors.forename: Bettina
authors.initials: B
authors.lastname: Bölter
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D008954:Models, Biological; D010940:Plant Proteins / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D021382:Protein Sorting Signals; D021381:Protein Transport / Q000187:drug effects; D054830:Sesterterpenes / Q000494:pharmacology; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013820:Thermolysin / Q000494:pharmacology; D014508:Urea
chemical_list: D060365:Chloroplast Proteins; D010940:Plant Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D054830:Sesterterpenes; C078737:chloroplast transit peptides; C002884:ophiobolins; D000255:Adenosine Triphosphate; D014508:Urea; D013820:Thermolysin