Chiu Chi-Chou, Li Hsou-Min
Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.
Plant J. 2008 Dec;56(5):793-801. doi: 10.1111/j.1365-313X.2008.03638.x. Epub 2008 Jul 23.
Chloroplast inner-membrane proteins Tic40 and Tic110 are first imported from the cytosol into the chloroplast stroma, and subsequently reinserted from the stroma into the inner membrane. However, the mechanism of reinsertion remains unclear. Here we show that Tic40 itself is involved in this reinsertion process. When precursors of either Tic40 or a Tic110 C-terminal truncate, tpTic110-Tic110N, were imported into chloroplasts isolated from a tic40-null mutant, soluble Tic40 and Tic110N intermediates accumulated in the stroma of tic40-mutant chloroplasts, due to a slower rate of reinsertion. We further show that a larger quantity of soluble Tic21 intermediates also accumulated in the stroma of tic40-mutant chloroplasts. In contrast, inner-membrane insertion of the triose-phosphate/phosphate translocator was not affected by the tic40 mutation. Our data suggest that multiple pathways exist for the insertion of chloroplast inner-membrane proteins.
叶绿体内膜蛋白Tic40和Tic110首先从细胞质溶胶导入叶绿体基质，随后从基质重新插入内膜。然而，重新插入的机制仍不清楚。在这里，我们表明Tic40自身参与了这一重新插入过程。当Tic40或Tic110 C端截短体tpTic110-Tic110N的前体导入从tic40缺失突变体分离的叶绿体时，由于重新插入速率较慢，可溶性Tic40和Tic110N中间体在tic40突变体叶绿体的基质中积累。我们进一步表明，大量可溶性Tic21中间体也在tic40突变体叶绿体的基质中积累。相比之下，磷酸丙糖/磷酸转运体的内膜插入不受tic40突变的影响。我们的数据表明，叶绿体内膜蛋白的插入存在多种途径。
