Specific lipids influence the import capacity of the chloroplast outer envelope precursor protein translocon

10.03.2012

Elkehal R, Becker T, Sommer MS, Königer M, Schleiff E.

Biochim Biophys Acta. 2012;1823(5):1033-40

Biochim Biophys Acta           online article

The translocase of the outer envelope membrane of chloroplasts (TOC complex) mediates the import of precursor proteins, which are synthesized on cytosolic ribosomes. The activity of the TOC complex is regulated by GTP-binding and hydrolysis. However, it is currently unclear whether the lipid composition of the outer envelope membrane affects the function of the TOC complex. To address this issue we employed two different strategies. First, isolated chloroplasts outer envelope vesicles from Pisum sativum were enriched with specific lipids by fusion with liposomes. Second, the TOC complex was reconstituted into liposomes with different lipid composition. In both experimental setups the TOC- mediated binding and transport of model precursor proteins was studied. We could demonstrate that sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylinositol (PI) stimulate binding to and transport across the TOC complex. In contrast, diacylgalactosyldiacylglycerol (DGDG) decreases the transport efficiency but supports binding of the precursor to the TOC machinery. Thus, we could show that specific lipids are important for the function of the TOC complex.