Gross Jeferson, Bhattacharya Debashish
University of Iowa, Department of Biology and the Roy J. Carver Center for Comparative Genomics, 446 Biology Building, Iowa City, IA 52242, USA.
Trends Plant Sci. 2009 Jan;14(1):13-20. doi: 10.1016/j.tplants.2008.10.003. Epub 2008 Nov 29.
The origin of the plastid from a cyanobacterial endosymbiont necessitated the establishment of specialized molecular machines (translocons) to facilitate the import of nuclear-encoded proteins into the organelle. To improve our understanding of the evolution of the translocons at the outer and inner envelope membrane of chloroplasts (Toc and Tic, respectively), we critically reassess the prevalent notion that their subunits have a function exclusive to protein import. We propose that many translocon components are multifunctional, conserving ancestral pre-endosymbiotic properties that predate their recruitment into the primitive translocon (putatively composed of subunits Toc34, Toc75 and Tic110 and associated chaperones). Multifunctionality seems to be a hallmark of the Tic complex, in which protein import is integrated with a broad array of plastid processes.
质体起源于蓝藻内共生体，这就需要建立专门的分子机器（转运体），以促进核编码蛋白导入该细胞器。为了更好地理解叶绿体内外膜转运体（分别为Toc和Tic）的进化，我们审慎地重新评估了一种普遍观点，即它们的亚基具有仅用于蛋白导入的功能。我们提出，许多转运体组分具有多种功能，保留了内共生之前的祖先特性，这些特性早于它们被招募到原始转运体中（推测由Toc34、Toc75和Tic110亚基以及相关伴侣蛋白组成）。多功能性似乎是Tic复合体的一个标志，其中蛋白导入与一系列广泛的质体过程相结合。
