The localization of Tic20 proteins in Arabidopsis thaliana is not restricted to the inner envelope membrane of chloroplasts
The localization of Tic20 proteins in Arabidopsis thaliana is not restricted to the inner envelope membrane of chloroplasts
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DOI：
10.1007/s11103-011-9818-5
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发表时间：
2011-11-01
影响因子：
5.1
通讯作者：
Schleiff, Enrico
中科院分区：
文献类型：
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作者：
Machettira, Anu B.;Gross, Lucia E.;Schleiff, Enrico
Tic 20是叶绿体内被膜前体蛋白易位子（TIC）的一个中心膜包埋组分。在拟南芥中，存在四种不同的Tic 20亚型。它们被注释为atTic 20-I、-II、-IV和-V，在胚植物门中形成两个不同的系统发育亚科。与atTic 20-I是叶绿体发育的唯一必需亚型相一致，我们表明该蛋白质专门针对叶绿体内被膜。对于atTic 20-II观察到相同的结果。相比之下，atTic 20-V定位于类囊体，atTic 20-IV双重定位于叶绿体和线粒体。这些结果与先前建立的表达谱一起解释了最近描述的Tic 20敲除植物的表型，并指向家族内这些蛋白质的功能多样化。对于所有的Tic 20蛋白，提出了一个4-螺旋拓扑结构，而不考虑靶向膜，这在一定程度上可以通过应用基于GFP的自组装拓扑结构方法在体内证实。通过同样的方法，我们发现，内被膜定位的Tic 20蛋白暴露其C-末端的叶绿体基质。考虑到所讨论的基质易位中间体，这种定位将与正内部规则一致。
Tic20 is a central, membrane-embedded component of the precursor protein translocon of the inner envelope of chloroplasts (TIC). In Arabidopsis thaliana, four different isoforms of Tic20 exist. They are annotated as atTic20-I, -II, -IV and -V and form two distinct phylogenetic subfamilies in embryophyta. Consistent with atTic20-I being the only essential isoform for chloroplast development, we show that the protein is exclusively targeted to the chloroplasts inner envelope. The same result is observed for atTic20-II. In contrast, atTic20-V is localized in thylakoids and atTic20-IV dually localizes to chloroplasts and mitochondria. These results together with the previously established expression profiles explain the recently described phenotypes of Tic20 knockout plants and point towards a functional diversification of these proteins within the family. For all Tic20 proteins a 4-helix topology is proposed irrespective of the targeted membrane, which in part could be confirmed in vivo by application of a self-assembling GFP-based topology approach. By the same approach we show that the inner envelope localized Tic20 proteins expose their C-termini to the chloroplast stroma. This localization would be consistent with the positive inside rule considering a stromal translocation intermediate as discussed.