PDF(Pubmed)
Abstract：
Selenocysteine (Sec) is encoded by the UGA codon that normally functions as a stop signal and is specifically incorporated into selenoproteins via a unique recoding mechanism. The translational recoding of UGA as Sec is directed by an unusual RNA structure, the SECIS element. Although archaea and eukaryotes adopt similar Sec encoding machinery, the SECIS elements have no similarities to each other with regard to sequence and structure. We analyzed >400 Asgard archaeal genomes to examine the occurrence of both Sec encoding system and selenoproteins in this archaeal superphylum, the closest prokaryotic relatives of eukaryotes. A comprehensive map of Sec utilization trait has been generated, providing the most detailed understanding of the use of this nonstandard amino acid in Asgard archaea so far. By characterizing the selenoproteomes of all organisms, several selenoprotein-rich phyla and species were identified. Most Asgard archaeal selenoprotein genes possess eukaryotic SECIS-like structures with varying degrees of diversity. Moreover, euryarchaeal SECIS elements might originate from Asgard archaeal SECIS elements via lateral gene transfer, indicating a complex and dynamic scenario of the evolution of SECIS element within archaea. Finally, a roadmap for the transition of eukaryotic SECIS elements from archaea was proposed, and selenophosphate synthetase may serve as a potential intermediate for the generation of ancestral eukaryotic SECIS element. Our results offer new insights into a deeper understanding of the evolution of Sec insertion machinery.
摘要：
硒代半胱氨酸（Sec）由UGA密码子编码，通常用作终止信号，并通过独特的重新编码机制特异性掺入硒蛋白中。UGA作为Sec的翻译重新编码是由一个不寻常的RNA结构指导的，Sec插入序列(SECIS)元素。尽管古细菌和真核生物采用了类似的Sec编码机制，SECIS元素在序列和结构方面没有相似之处。我们分析了400多个Asgard古细菌基因组，以检查该古细菌超门中Sec编码系统和硒蛋白的发生，真核生物的近亲。已经生成了Sec利用性状的全面图谱，提供了迄今为止在Asgard古细菌中使用这种非标准氨基酸的最详细的了解。通过表征所有生物体的硒蛋白质组，鉴定了几种富含硒蛋白的门和物种。大多数Asgard古细菌硒蛋白基因具有真核SECIS样结构，具有不同程度的多样性。此外，原始SECIS元件可能通过侧向基因转移起源于Asgard原始SECIS元件，表明古细菌中SECIS元素演化的复杂而动态的情景。最后,提出了从古细菌中转移真核SECIS元素的路线图，和硒磷酸合成酶可以作为产生祖先真核SECIS元件的潜在中间体。我们的结果为更深入地了解Sec插入机械的发展提供了新的见解。
