title: Specific lipids influence the import capacity of the chloroplast outer envelope precursor protein translocon.
abstract: Recent studies demonstrated that lipids influence the assembly and efficiency of membrane-embedded macromolecular complexes. Similarly, lipids have been found to influence chloroplast precursor protein binding to the membrane surface and to be associated with the Translocon of the Outer membrane of Chloroplasts (TOC). We used a system based on chloroplast outer envelope vesicles from Pisum sativum to obtain an initial understanding of the influence of lipids on precursor protein translocation across the outer envelope. The ability of the model precursor proteins p(OE33)titin and pSSU to be recognized and translocated in this simplified system was investigated. We demonstrate that transport across the outer membrane can be observed in the absence of the inner envelope translocon. The translocation, however, was significantly slower than that observed for chloroplasts. Enrichment of outer envelope vesicles with different lipids natively found in chloroplast membranes altered the binding and transport behavior. Further, the results obtained using outer envelope vesicles were consistent with the results observed for the reconstituted isolated TOC complex. Based on both approaches we concluded that the lipids sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylinositol (PI) increased TOC-mediated binding and import for both precursor proteins. In contrast, enrichment in digalactosyldiacylglycerol (DGDG) improved TOC-mediated binding for pSSU, but decreased import for both precursor proteins. Optimal import occurred only in a narrow concentration range of DGDG.
authors.affiliation: Center of Membrane Proteomic, Molecular Cell Biology of Plants, Goethe-University, Max-von-Laue-Str. 9, D-60438 Frankfurt, Germany.
authors.forename: Rajae
authors.initials: R
authors.lastname: Elkehal
authors.forename: Thomas
authors.initials: T
authors.lastname: Becker
authors.forename: Maik S
authors.initials: MS
authors.lastname: Sommer
authors.forename: Martina
authors.initials: M
authors.lastname: Königer
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
mesh_terms: D060365:Chloroplast Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000378:metabolism; D038983:Galactolipids / Q000494:pharmacology; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D008055:Lipids / Q000494:pharmacology*; D018532:Pisum sativum / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011498:Protein Precursors / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D053835:Unilamellar Liposomes / Q000378:metabolism
chemical_list: D060365:Chloroplast Proteins; D005456:Fluorescent Dyes; D038983:Galactolipids; D008055:Lipids; D011498:Protein Precursors; D053835:Unilamellar Liposomes; C007388:digalactosyldiacylglycerol; C009909:monogalactosyldiacylglycerol; D012273:Ribulose-Bisphosphate Carboxylase