Robinson C, Thompson S J, Woolhead C
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, United Kingdom.
Traffic. 2001 Apr;2(4):245-51. doi: 10.1034/j.1600-0854.2001.1r010.x.
The assembly of the chloroplast thylakoid membrane requires the import of numerous proteins from the cytosol and their targeting into or across the thylakoid membrane. It is now clear that multiple pathways are involved in the thylakoid-targeting stages, depending on the type of protein substrate. Two very different pathways are used by thylakoid lumen proteins; one is the Sec pathway which has been well-characterised in bacteria, and which involves the threading of the substrate through a narrow channel. In contrast, the more recently characterised twin-arginine translocation (Tat) system is able to translocate fully folded proteins across this membrane. Recent advances on bacterial Tat systems shed further light on the structure and function of this system. Membrane proteins, on the other hand, use two further pathways. One is the signal recognition particle-dependent pathway, involving a complex interplay between many different factors, whereas other proteins insert without the assistance of any known apparatus. This article reviews advances in the study of these pathways and considers the rationale behind the surprising complexity.
叶绿体类囊体膜的组装需要从细胞质中导入大量蛋白质，并将它们靶向导入类囊体膜或穿过类囊体膜。现在很清楚，根据蛋白质底物的类型，类囊体靶向阶段涉及多种途径。类囊体腔蛋白使用两种截然不同的途径；一种是Sec途径，它在细菌中已得到充分表征，涉及底物穿过狭窄通道的穿膜过程。相比之下，最近表征的双精氨酸转运（Tat）系统能够将完全折叠的蛋白质转运穿过此膜。细菌Tat系统的最新进展进一步揭示了该系统的结构和功能。另一方面，膜蛋白使用另外两种途径。一种是依赖信号识别颗粒的途径，涉及许多不同因子之间的复杂相互作用，而其他蛋白质则在没有任何已知装置协助的情况下插入。本文综述了这些途径研究的进展，并思考了这种惊人复杂性背后的基本原理。
