Evolution of Elongation Factor G and the Origins of Mitochondrial and Chloroplast Forms
Evolution of Elongation Factor G and the Origins of Mitochondrial and Chloroplast Forms
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DOI：
10.1093/molbev/msq316
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发表时间：
2011-03-01
影响因子：
10.7
通讯作者：
Baldauf, Sandra L.
中科院分区：
文献类型：
--
作者：
Atkinson, Gemma C.;Baldauf, Sandra L.
蛋白质合成延长因子G（EF-G）是一种重要的蛋白质，在蛋白质合成的延长和核糖体再循环阶段起着重要作用。虽然EF-G进化被预测为保守的，但最近的报告表明并非如此。我们的特点EF-G在其分子遗传学，基因组背景下，和模式的氨基酸取代。我们发现，大多数细菌携带一个单一的“规范”EF-G，这是遗传保守的，并在一个str操纵子编码。然而，我们也发现了一些EF-G旁系同源物。这些包括一对EF-G，它们大多在一起发现，并在一个折衷的细菌亚群中发现，特别是δ-变形菌，螺旋体和浮游菌（“spd”细菌）。这些spdEFG也引起了线粒体因子mtEFG 1和mtEFG 2，它们可能在真核生物最后的共同祖先之前到达真核生物。同时，叶绿体显然使用α-变形菌衍生的EF-G，而不是预期的蓝藻形式。spd/mtEFG的长期维持可能与其易位和核糖体再循环的亚功能化有关。与此一致，序列保守性和位点特异性进化速率变化的模式表明，进化更快的spd/mtEFG 2已经失去了易位功能，但令人惊讶的是，该蛋白质也显示出与回收活性相关的位点几乎没有保守性。另一方面，spd/mtEFG 1，虽然更缓慢地演变，显示出实质性重塑的迹象。这在GT3结构域中特别广泛，包括开关I中高度保守的三个氨基酸插入。我们认为，亚功能化的spd/mtEFG是不是一个简单的情况下，专业化的原始活动的子集。相反，复制允许从双重功能强加的选择性约束中释放一个paranum，从而使其变得更加高度专业化。因此，亚功能化提供的微调潜力可以解释EF-G旁系同源物的维持。
Protein synthesis elongation factor G (EF-G) is an essential protein with central roles in both the elongation and ribosome recycling phases of protein synthesis. Although EF-G evolution is predicted to be conservative, recent reports suggest otherwise. We have characterized EF-G in terms of its molecular phylogeny, genomic context, and patterns of amino acid substitution. We find that most bacteria carry a single "canonical" EF-G, which is phylogenetically conservative and encoded in an str operon. However, we also find a number of EF-G paralogs. These include a pair of EF-Gs that are mostly found together and in an eclectic subset of bacteria, specifically delta-proteobacteria, spirochaetes, and planctomycetes (the "spd" bacteria). These spdEFGs have also given rise to the mitochondrial factors mtEFG1 and mtEFG2, which probably arrived in eukaryotes before the eukaryotic last common ancestor. Meanwhile, chloroplasts apparently use an alpha-proteobacterial-derived EF-G rather than the expected cyanobacterial form. The long-term comaintenance of the spd/mtEFGs may be related to their subfunctionalization for translocation and ribosome recycling. Consistent with this, patterns of sequence conservation and site-specific evolutionary rate shifts suggest that the faster evolving spd/mtEFG2 has lost translocation function, but surprisingly, the protein also shows little conservation of sites related to recycling activity. On the other hand, spd/mtEFG1, although more slowly evolving, shows signs of substantial remodeling. This is particularly extensive in the GTPase domain, including a highly conserved three amino acid insertion in switch I. We suggest that subfunctionalization of the spd/mtEFGs is not a simple case of specialization for subsets of original activities. Rather, the duplication allows the release of one paralog from the selective constraints imposed by dual functionality, thus allowing it to become more highly specialized. Thus, the potential for fine tuning afforded by subfunctionalization may explain the maintenance of EF-G paralogs.