Reconstituting a chloroplast transport system

In the first successful reconstitution of a chloroplast transport system, only three proteins are required for GTP-dependent translocation of preproteins into proteoliposomes, according to Enrico Schleiff, Marko Jelic, and Jürgen Soll (Maximilian Universität München, Munich, Germany). Based on this in vitro system, the authors propose that the preprotein first binds to Toc34 in a GTP-dependent manner and is then passed off to Toc159, which pushes the polypeptide through the Toc75 channel itself, also in a GTP-dependent process.

“We were rather surprised that such a minimal system could actually translocate a protein,” says Schleiff. It was previously thought that molecular chaperones associated with the Tic complex generated the force to drive the protein through the channel.

Combining the new results with structural information, which shows the ratio of Toc34, Toc75, and Toc159 in an assembled channel...