Vothknecht Ute C, Soll Jürgen
Department of Biology I, Botanisches Institut der LMU München, Menzinger Street 67, München D-80638, Germany.
Gene. 2005 Jul 18;354:99-109. doi: 10.1016/j.gene.2005.04.021.
Chloroplasts are specific plant organelles of prokaryotic origin. They are separated from the surrounding cell by a double membrane, which represents an effective barrier for the transport of metabolites and proteins. Specific transporters in the inner envelope membrane have been described, which facilitate the exchange of metabolites. In contrast, the outer envelope has been viewed for a long time as a molecular sieve that offers a mere size constriction to the passage of molecules. This view has been challenged lately, and a number of specific and regulated pore proteins of the outer envelope (OEPs) have been identified. These pores seem to have originated by adaptation of outer membrane proteins of the cyanobacterial ancestor of the chloroplast. In a similar fashion, the transport of proteins across the two envelope membranes is achieved by two hetero-oligomeric protein complexes called Toc (translocon in the outer envelope of chloroplasts) and Tic (translocon in the inner envelope of chloroplasts). The phylogenetic provenance of the translocon components is less clear, but at least the channel protein of the Toc translocon is of cyanobacterial origin. Characteristic of cyanobacteria and chloroplasts is furthermore a specialized internal membrane system, the thylakoids, on which the components of the photosynthetic machinery are located. Despite the importance of this membrane, very little is known about its phylogenetic origin or the manner of its synthesis. Vipp1 appears to be a ubiquitous component of thylakoid formation, while in chloroplasts of land plants, additionally a vesicle transport system of eukaryotic origin might be involved in this process.
叶绿体是起源于原核生物的特定植物细胞器。它们通过双层膜与周围的细胞分隔开，这层膜对代谢物和蛋白质的运输构成了有效的屏障。内膜上已经发现了特定的转运蛋白，它们促进代谢物的交换。相比之下，外膜长期以来一直被视为一种分子筛，对分子的通过仅提供大小限制。最近这种观点受到了挑战，并且已经鉴定出一些外膜的特定且受调控的孔蛋白（OEPs）。这些孔似乎是由叶绿体蓝藻祖先的外膜蛋白适应进化而来的。同样，蛋白质穿过两层包膜的运输是由两种异源寡聚蛋白复合物完成的，分别称为Toc（叶绿体外膜转运体）和Tic（叶绿体内膜转运体）。转运体成分的系统发育起源尚不清楚，但至少Toc转运体的通道蛋白起源于蓝藻。蓝藻和叶绿体的另一个特征是一种特殊的内膜系统——类囊体，光合机构的组成部分位于其上。尽管这种膜很重要，但关于其系统发育起源或合成方式却知之甚少。Vipp1似乎是类囊体形成的普遍成分，而在陆地植物的叶绿体中，此外一个真核起源的囊泡运输系统可能也参与了这个过程。
