A 1-megadalton translocation complex containing Tic20 and Tic21 mediates chloroplast protein import at the inner envelope membrane.
Chloroplast protein import is mediated by two hetero-oligomeric protein complexes, the Tic and Toc translocons, which are located in the inner and outer envelope membranes. At the inner membrane, many Tic components have been identified and characterized, but it remains unclear how these Tic proteins are organized to form a protein-conducting channel or whether a stable Tic core complex that binds translocating preproteins exists. Here, we report the identification of a 1-megadalton (MD) translocation complex as an intermediate during protein translocation across the inner membrane in Arabidopsis thaliana and pea (Pisum sativum). This complex can be detected by blue native PAGE using the mild detergent digitonin without any chemical cross-linkers. The preprotein arrested in the 1-MD complex can be chased into its fully translocated form after a subsequent incubation. While Tic20 and Tic21 appear to be involved in the 1-MD complex, Tic110, a well-characterized Tic component, exists as a distinct entity from the complex. Several lines of evidence suggest that the 1-MD complex functions in between the Toc and Tic110-containing complexes, most likely as a protein-conducting channel at the inner envelope.
Kikuchi
Shingo
S
Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan.
Oishi
Maya
M
Hirabayashi
Yoshino
Y
Lee
Dong Wook
DW
Hwang
Inhwan
I
Nakai
Masato
M
D000255:Adenosine Triphosphate / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006160:Guanosine Triphosphate / Q000378:metabolism; D006706:Homeostasis / Q000235:genetics; D007501:Iron / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009154:Mutation; D018532:Pisum sativum / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D021381:Protein Transport / Q000235:genetics; D013820:Thermolysin / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology
D000255:Adenosine Triphosphate; D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D006160:Guanosine Triphosphate; D007501:Iron; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D013820:Thermolysin; D014357:Trypsin; C457764:Tic20 protein, Arabidopsis; C116000:Tic20 protein, Pisum sativum; C116001:Tic22 protein, Pisum sativum; C520843:At2g15290 protein, Arabidopsis