Cline K, Henry R
Horticultural Sciences Department, University of Florida, Gainesville 32611, USA.
Annu Rev Cell Dev Biol. 1996;12:1-26. doi: 10.1146/annurev.cellbio.12.1.1.
Most chloroplast proteins are nuclear encoded, synthesized as larger precursor proteins in the cytosol, posttranslationally imported into the organelle, and routed to one of six different compartments. Import across the outer and inner envelope membranes into the stroma is the major means for entry of proteins destined for the stroma, the thylakoid membrane, and the thylakoid lumen. Recent investigations have identified several unique protein components of the envelope translocation machinery. These include two GTP-binding proteins that appear to participate in the early events of import and probably regulate precursor recognition and advancement into the translocon. Localization of imported precursor proteins to the thylakoid membrane and thylakoid lumen is accomplished by four distinct mechanisms; two are homologous to bacterial and endoplasmic reticulum protein transport systems, one appears unique, and the last may be a spontaneous mechanism. Thus chloroplast protein targeting is a unique and surprisingly complex process. The presence of GTP-binding proteins in the envelope translocation machinery indicates a different precursor recognition process than is present in mitochondria. Mechanisms for thylakoid protein localization are in part derived from the prokaryotic endosymbiont, but are more unusual and diverse than expected.
大多数叶绿体蛋白是由核基因编码的，在细胞质中作为较大的前体蛋白合成，经翻译后导入该细胞器，并被输送到六个不同的区室之一。穿过外膜和内膜进入基质是蛋白质进入基质、类囊体膜和类囊体腔的主要途径。最近的研究已经确定了包膜转运机制的几个独特的蛋白质成分。其中包括两种GTP结合蛋白，它们似乎参与了导入的早期事件，可能调节前体的识别和进入转运体的过程。导入的前体蛋白定位于类囊体膜和类囊体腔是通过四种不同的机制完成的；其中两种与细菌和内质网蛋白运输系统同源，一种似乎是独特的，最后一种可能是自发机制。因此，叶绿体蛋白靶向是一个独特且惊人复杂的过程。包膜转运机制中GTP结合蛋白的存在表明其前体识别过程与线粒体中的不同。类囊体蛋白定位机制部分源自原核内共生体，但比预期的更为独特和多样。
