Schünemann Danja
Lehrstuhl für Allgemeine und Molekulare Botanik, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Biol Chem. 2007 Sep;388(9):907-15. doi: 10.1515/BC.2007.111.
The thylakoid membrane of chloroplasts contains the major photosynthetic complexes, which consist of several either nuclear or chloroplast encoded subunits. The biogenesis of these thylakoid membrane complexes requires coordinated transport and subsequent assembly of the subunits into functional complexes. Nuclear-encoded thylakoid proteins are first imported into the chloroplast and then directed to the thylakoid using different sorting mechanisms. The cpSec pathway and the cpTat pathway are mainly involved in the transport of lumenal proteins, whereas the spontaneous pathway and the cpSRP pathway are used for the insertion of integral membrane proteins into the thylakoid membrane. While cpSec-, cpTat- and cpSRP-mediated targeting can be classified as 'assisted' mechanisms involving numerous components, 'unassisted' spontaneous insertion does not require additional targeting factors. However, even the assisted pathways differ fundamentally with respect to stromal targeting factors, the composition of the translocase and energy requirements.
叶绿体的类囊体膜包含主要的光合复合体，这些复合体由几个核编码或叶绿体编码的亚基组成。这些类囊体膜复合体的生物发生需要亚基的协调运输以及随后组装成功能复合体。核编码的类囊体蛋白首先被导入叶绿体，然后通过不同的分选机制被导向类囊体。叶绿体Sec途径和叶绿体Tat途径主要参与腔蛋白的运输，而自发途径和叶绿体信号识别颗粒（cpSRP）途径则用于将整合膜蛋白插入类囊体膜。虽然叶绿体Sec、叶绿体Tat和叶绿体信号识别颗粒介导的靶向可归类为涉及众多组分的“辅助”机制，但“非辅助”的自发插入不需要额外的靶向因子。然而，即使是辅助途径在基质靶向因子、转位酶的组成和能量需求方面也存在根本差异。
