Functional Evolution in Orthologous Cell-encoded RNA-dependent RNA Polymerases.
Functional Evolution in Orthologous Cell-encoded RNA-dependent RNA Polymerases.
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DOI：
10.1074/jbc.m115.685933
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发表时间：
2016-04-22
期刊：
影响因子：
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通讯作者：
Lescar J
中科院分区：
文献类型：
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作者：
Qian X;Hamid FM;El Sahili A;Darwis DA;Wong YH;Bhushan S;Makeyev EV;Lescar J
许多真核生物编码不止一种 RNA 依赖性 RNA 聚合酶 (RdRP)，这些酶可能是基因复制的结果。此类 RdRP 旁系同源物通常参与不同的 RNA 沉默途径，并在体外显示出特征性的酶活性。然而，单个旁系同源群体的成员在物种形成过程中能在多大程度上经历功能变化仍然是一个悬而未决的问题。我们发现，QDE-1 的直系同源物（粗糙脉孢菌抑制途径的 RdRP 成分）在氨基酸序列水平的进化中迅速分化。对来自粗糙脉孢菌 (QDE-1Ncr) 和相关真菌土生梭孢霉 (QDE-1Tte) 和嗜热毁丝霉 (QDE-1Mth) 的纯化 QDE-1 聚合酶的分析表明，所有三种酶都可以合成 RNA，但其作用的精确模式差异很大。与支持持续 RNA 合成的 QDE-1Ncr 对应物不同，QDE-1Tte 和 QDE-1Mth 通过不依赖引物的启动主要产生短 RNA 拷贝。令人惊讶的是，QDE-1Tte 的 3.19 Å 分辨率晶体结构揭示了与 QDE-1Ncr 类似的准对称二聚体。进一步的电子显微镜分析证实，QDE-1Tte 在溶液中以二聚体形式存在，并在与模板相互作用后保留这种状态。我们得出的结论是，直系同源 RdRP 的分歧可以导致功能创新，同时保留整体蛋白质折叠和四级结构。
Many eukaryotic organisms encode more than one RNA-dependent RNA polymerase (RdRP) that probably emerged as a result of gene duplication. Such RdRP paralogs often participate in distinct RNA silencing pathways and show characteristic repertoires of enzymatic activities in vitro. However, to what extent members of individual paralogous groups can undergo functional changes during speciation remains an open question. We show that orthologs of QDE-1, an RdRP component of the quelling pathway in Neurospora crassa, have rapidly diverged in evolution at the amino acid sequence level. Analyses of purified QDE-1 polymerases from N. crassa (QDE-1Ncr) and related fungi, Thielavia terrestris (QDE-1Tte) and Myceliophthora thermophila (QDE-1Mth), show that all three enzymes can synthesize RNA, but the precise modes of their action differ considerably. Unlike their QDE-1Ncr counterpart favoring processive RNA synthesis, QDE-1Tte and QDE-1Mth produce predominantly short RNA copies via primer-independent initiation. Surprisingly, a 3.19 Å resolution crystal structure of QDE-1Tte reveals a quasisymmetric dimer similar to QDE-1Ncr. Further electron microscopy analyses confirm that QDE-1Tte occurs as a dimer in solution and retains this status upon interaction with a template. We conclude that divergence of orthologous RdRPs can result in functional innovation while retaining overall protein fold and quaternary structure.