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Updated: Aug 13, 2026

Studying Protein Import into Chloroplasts Using Protoplasts
Published on: December 10, 2018
Characterization of the preprotein translocon at the outer envelope membrane of chloroplasts by blue native PAGE
Shingo Kikuchi1, Toshiya Hirohashi, Masato Nakai
1Institute for Protein Research, Osaka University, Suita, Japan.
Abstract:
The preprotein translocon at the outer envelope membrane of chloroplasts (Toc) mediates the recognition and import of nuclear-encoded preproteins into chloroplasts. Two receptor components, Toc159 and Toc34, and the channel Toc75 form the Toc complex. In this study, we have analyzed the molecular architecture and organization of the Toc complex by blue native PAGE (BN-PAGE), which is a high-resolution method for separating membrane protein complexes under non-denaturing conditions. Pea chloroplasts isolated in the presence of a protease inhibitor cocktail were directly solubilized in detergent solution and analyzed by BN-PAGE and size exclusion chromatography. Subsequent immunoblot analyses indicated that the complex composed of Toc75, Toc159 and Toc34 has a molecular mass of 800-1,000 kDa. Limited proteolysis revealed a core of the Toc complex, which was resistant to proteases and detergent treatments. The stoichiometry of the three Toc proteins was calculated as approximately 1 : 3 : 3 between Toc159 : Toc75 : Toc34. We have also analyzed the Toc complex of etioplasts and root plastids. These plastids were found to have essentially the same sized Toc complex as that of the chloroplast.
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