Bédard Jocelyn, Jarvis Paul
Department of Biology, University of Leicester, University Road, Leicester LE1 7RH, UK.
J Exp Bot. 2005 Sep;56(419):2287-320. doi: 10.1093/jxb/eri243. Epub 2005 Aug 8.
Plastids are a diverse group of plant organelles that perform essential functions including important steps in many biosynthetic pathways. Chloroplasts are the best characterized type of plastid, and constitute the site of oxygenic photosynthesis in plants, a process essential to all higher life forms. It is well established that the majority (>90%) of chloroplast proteins are nucleus-encoded and must be post-translationally imported into these envelope-bound compartments. Most nucleus-encoded chloroplast proteins are translated in precursor form on cytosolic ribosomes, targeted to the chloroplast surface, and then imported across the double-membrane envelope by translocons in the outer and inner envelope membranes of the chloroplast, termed TOC and TIC, respectively. Recently, significant progress has been made in our understanding of how proteins are targeted to the chloroplast surface and translocated across the chloroplast envelope into the stroma. Evidence suggesting the existence of multiple import pathways at the outer envelope membrane for different classes of precursor proteins has been presented. These pathways appear to utilize similar TOC complexes equipped with different combinations of homologous GTPase receptors, providing preprotein recognition specificity.
质体是植物细胞器的一个多样化群体，执行着包括许多生物合成途径中的重要步骤在内的基本功能。叶绿体是特征最为明确的质体类型，是植物中进行放氧光合作用的场所，而这一过程对所有高等生命形式都至关重要。众所周知，叶绿体中大多数（>90%）蛋白质是由细胞核编码的，必须在翻译后导入到这些被包膜包围的区室中。大多数由细胞核编码的叶绿体蛋白质以前体形式在细胞质核糖体上翻译，被靶向运送到叶绿体表面，然后通过叶绿体外膜和内膜中的转运体分别称为TOC和TIC，跨双膜包膜导入。最近，我们在理解蛋白质如何被靶向运送到叶绿体表面并穿过叶绿体包膜进入基质方面取得了重大进展。已经有证据表明，对于不同类别的前体蛋白，在外膜存在多种导入途径。这些途径似乎利用配备有不同同源GTPase受体组合的相似TOC复合物，从而提供前体蛋白识别特异性。
