Uncovering the protein translocon at the chloroplast inner envelope membrane.
Chloroplasts require protein translocons at the outer and inner envelope membranes, termed TOC and TIC, respectively, to import thousands of cytoplasmically synthesized preproteins. However, the molecular identity of the TIC translocon remains controversial. Tic20 forms a 1-megadalton complex at the inner membrane and directly interacts with translocating preproteins. We purified the 1-megadalton complex from Arabidopsis, comprising Tic20 and three other essential components, one of which is encoded by the enigmatic open reading frame ycf1 in the chloroplast genome. All four components, together with well-known TOC components, were found stoichiometrically associated with different translocating preproteins. When reconstituted into planar lipid bilayers, the purified complex formed a preprotein-sensitive channel. Thus, this complex constitutes a general TIC translocon.
Laboratory of Regulation of Biological Reactions, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, Japan.
Shingo
S
Kikuchi
Jocelyn
J
Bédard
Minako
M
Hirano
Yoshino
Y
Hirabayashi
Maya
M
Oishi
Midori
M
Imai
Mai
M
Takase
Toru
T
Ide
Masato
M
Nakai
D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D019143:Evolution, Molecular; D055786:Gene Knockout Techniques; D008051:Lipid Bilayers / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D009154:Mutation; D016366:Open Reading Frames; D021381:Protein Transport
D029681:Arabidopsis Proteins; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins; C457764:Tic20 protein, Arabidopsis