Protein transport in organelles: The Toc complex way of preprotein import.
Most of the estimated 1000 or so chloroplast proteins are synthesized as cytosolic preproteins with N-terminal cleavable targeting sequences (transit peptide). Translocon complexes at the outer (Toc) and inner chloroplast envelope membrane (Tic) concertedly facilitate post-translational import of preproteins into the chloroplast. Three components, the Toc34 and Toc159 GTPases together with the Toc75 channel, form the core of the Toc complex. The two GTPases act as GTP-dependent receptors at the chloroplast surface and promote insertion of the preprotein across the Toc75 channel. Additional factors guide preproteins to the Toc complex or support their stable ATP-dependent binding to the chloroplast. This minireview describes the components of the Toc complex and their function during the initial steps of preprotein translocation across the chloroplast envelope.
Agne
Birgit
B
Laboratoire de Physiologie Végétale, Université de Neuchâtel, Switzerland.
Kessler
Felix
F
D029681:Arabidopsis Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008954:Models, Biological; D015388:Organelles / Q000378:metabolism; D010766:Phosphorylation; D011498:Protein Precursors / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology
D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D011498:Protein Precursors; C403444:TOC159 protein, Arabidopsis; C491798:TOC34 protein, Arabidopsis; C491244:TOC75 protein, Arabidopsis; D020558:GTP Phosphohydrolases