The stability and processing of cellular RNA transcripts are efficiently controlled via non-templated addition of single or multiple nucleotides, which is catalyzed by various nucleotidyltransferases including poly(A) polymerases (PAPs). Germline development defective 2 (GLD-2) is among the first reported cytoplasmic non-canonical PAPs that promotes the translation of germline-specific mRNAs by extending their short poly(A) tails in metazoan, such as Caenorhabditis elegans and Xenopus. On the other hand, the function of mammalian GLD-2 seems more diverse, which includes monoadenylation of certain microRNAs. To understand the structural basis that underlies the difference between mammalian and non-mammalian GLD-2 proteins, we determine crystal structures of two rodent GLD-2s. Different from C. elegans GLD-2, mammalian GLD-2 is an intrinsically robust PAP with an extensively positively charged surface. Rodent and C. elegans GLD-2s have a topological difference in the β-sheet region of the central domain. Whereas C. elegans GLD-2 prefers adenosine-rich RNA substrates, mammalian GLD-2 can work on RNA oligos with various sequences. Coincident with its activity on microRNAs, mammalian GLD-2 structurally resembles the mRNA and miRNA processor terminal uridylyltransferase 7 (TUT7). Our study reveals how GLD-2 structurally evolves to a more versatile nucleotidyltransferase, and provides important clues in understanding its biological function in mammals.

中文翻译：

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哺乳动物GLD-2蛋白的结构揭示了其在mRNA和microRNA加工中功能多样性的分子基础。

可以通过非模板添加单个或多个核苷酸来有效控制细胞RNA转录物的稳定性和加工过程，该过程可通过多种核苷酸转移酶（包括poly（A）聚合酶（PAP））来催化。生殖细胞发育缺陷2（GLD-2）是最早报道的胞质非规范PAP之一，其通过延伸后生动物的短poly（A）尾巴（例如秀丽隐杆线虫和非洲爪蟾）来促进种系特异性mRNA的翻译。。另一方面，哺乳动物GLD-2的功能似乎更加多样化，其中包括某些microRNA的单腺苷酸化。要了解构成哺乳动物和非哺乳动物GLD-2蛋白之间差异的基础，我们确定了两种啮齿动物GLD-2的晶体结构。与C不同。线虫GLD-2，哺乳动物GLD-2是一种内在坚固的PAP，表面带大量正电荷。鼠类和Ç。线虫GLD-2在中央结构域的β-折叠区域中具有拓扑差异。而Ç。线虫GLD-2更喜欢富含腺苷的RNA底物，哺乳动物GLD-2可以对具有各种序列的RNA寡核苷酸起作用。与其在microRNA上的活性相吻合，哺乳动物GLD-2在结构上类似于mRNA和miRNA处理器末端的uridylyltransferase 7（TUT7）。我们的研究揭示了GLD-2如何在结构上进化为更通用的核苷酸转移酶，并为了解其在哺乳动物中的生物学功能提供了重要线索。