Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
Dept. Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ 08854, USA.
Nucleic Acids Res. 2020 Jun 19;48(11):6136-6148. doi: 10.1093/nar/gkaa297.
In eukaryotes, the DXO/Rai1 enzymes can eliminate most of the incomplete and non-canonical NAD caps through their decapping, deNADding and pyrophosphohydrolase activities. Here, we report that these enzymes can also remove FAD and dephospho-CoA (dpCoA) non-canonical caps from RNA, and we have named these activities deFADding and deCoAping. The crystal structures of mammalian DXO with 3'-FADP or CoA and fission yeast Rai1 with 3'-FADP provide elegant insight to these activities. FAD and CoA are accommodated in the DXO/Rai1 active site by adopting folded conformations. The flavin of FAD and the pantetheine group of CoA contact the same region at the bottom of the active site tunnel, which undergoes conformational changes to accommodate the different cap moieties. We have developed FAD-capQ to detect and quantify FAD-capped RNAs and determined that FAD caps are present on short RNAs (with less than ∼200 nucleotides) in human cells and that these RNAs are stabilized in the absence of DXO.
在真核生物中，DXO/Rai1 酶可以通过脱帽、去 NAD 和焦磷酸水解酶活性来消除大多数不完整和非规范的 NAD 帽。在这里，我们报告这些酶也可以从 RNA 上去除 FAD 和去磷酸辅酶 A（dpCoA）非规范帽，并将这些活性命名为脱 FAD 和去 CoA。具有 3'-FADP 或 CoA 的哺乳动物 DXO 和具有 3'-FADP 的裂殖酵母 Rai1 的晶体结构为这些活性提供了优雅的见解。FAD 和 CoA 通过采用折叠构象被容纳在 DXO/Rai1 的活性部位中。FAD 的黄素和 CoA 的泛酸基团与活性部位隧道底部的同一区域接触，该区域发生构象变化以容纳不同的帽部分。我们开发了 FAD-capQ 来检测和定量 FAD 帽 RNA，并确定 FAD 帽存在于人类细胞中的短 RNA（少于约 200 个核苷酸）上，并且在没有 DXO 的情况下这些 RNA 得到稳定。
