Ziehe Dominik, Dünschede Beatrix, Schünemann Danja
Molecular Biology of Plant Organelles, Ruhr University Bochum, Universitätsstraße 150, D-44780 Bochum.
Biol Chem. 2017 May 1;398(5-6):653-661. doi: 10.1515/hsz-2016-0292.
Chloroplasts derive from a prokaryotic symbiont that lost most of its genes during evolution. As a result, the great majority of chloroplast proteins are encoded in the nucleus and are posttranslationally imported into the organelle. The chloroplast genome encodes only a few proteins. These include several multispan thylakoid membrane proteins which are synthesized on thylakoid-bound ribosomes and cotranslationally inserted into the membrane. During evolution, ancient prokaryotic targeting machineries were adapted and combined with novel targeting mechanisms to facilitate post- and cotranslational protein transport in chloroplasts. This review focusses on the chloroplast signal recognition particle (cpSRP) protein transport system, which has been intensively studied in higher plants. The cpSRP system derived from the prokaryotic SRP pathway, which mediates the cotranslational protein transport to the bacterial plasma membrane. Chloroplasts contain homologs of several components of the bacterial SRP system. The function of these conserved components in post- and/or cotranslational protein transport and chloroplast-specific modifications of these transport mechanisms are described. Furthermore, recent studies of cpSRP systems in algae and lower plants are summarized and their impact on understanding the evolution of the cpSRP system are discussed.
叶绿体起源于一种原核共生体，该共生体在进化过程中丢失了大部分基因。因此，绝大多数叶绿体蛋白是由细胞核编码，并在翻译后导入该细胞器。叶绿体基因组仅编码少数几种蛋白质。这些蛋白质包括几种多跨类囊体膜蛋白，它们在类囊体结合核糖体上合成，并在翻译过程中插入膜中。在进化过程中，古老的原核靶向机制经过改造，并与新的靶向机制相结合，以促进叶绿体中翻译后和翻译过程中的蛋白质运输。本综述重点关注叶绿体信号识别颗粒（cpSRP）蛋白运输系统，该系统已在高等植物中得到深入研究。cpSRP系统起源于原核生物的SRP途径，该途径介导翻译过程中的蛋白质运输到细菌质膜。叶绿体含有细菌SRP系统几个组分的同源物。描述了这些保守组分在翻译后和/或翻译过程中的蛋白质运输中的功能，以及这些运输机制的叶绿体特异性修饰。此外，总结了近期对藻类和低等植物中cpSRP系统的研究，并讨论了它们对理解cpSRP系统进化的影响。
