Structural basis for tRNA methylthiolation by the radical SAM enzyme MiaB.
Structural basis for tRNA methylthiolation by the radical SAM enzyme MiaB.
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tRNA通过自由基SAM酶MiaB甲基硫醇化的结构基础。
DOI：
10.1038/s41586-021-03904-6
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发表时间：
2021-09
期刊：
影响因子：
64.8
通讯作者：
中科院分区：
文献类型：
--
作者：
许多转录后修饰的转移RNA(TRNA)在翻译中起着至关重要的作用。2-甲硫基-N6-异戊烯基腺苷(Ms2i6A)修饰发生在反密码子36位含腺嘌呤的tRNA的37(A37)位，用于促进有效的A：U密码子-反密码子碱基配对，并防止近同源物的意外碱基配对，从而提高翻译保真度。MIAB是一种自由基S-腺苷甲硫氨酸甲硫基转移酶(MTTase)，ms2I6A修饰是通过MIAB将ms2I6A连接到异戊烯基腺苷(I6A)上。作为一种自由基SAM蛋白，MIAB含有一个[Fe4S4]RS簇，用于SAM的还原裂解，形成5‘-脱氧腺苷5’-自由基(5‘-da·)，负责去除底物的C2氢。MIAB还包含一个辅助的[Fe4S4]Aux簇，它参与了i6A37向C2的硫转移。这种转移是如何发生的，在很大程度上是未知的。在此，我们介绍了均匀拟杆菌MIAB(BuMiaB)的几种结构。这些结构符合两步机制，其中一个SAM分子首先被用来甲基化辅助簇的桥联μ-硫离子。在第二步中，第二个SAM分子被裂解成5‘-da·，它提取底物的C2氢，但在C2从Sp2重新杂交到Sp3之后。这项工作促进了我们对酶如何使惰性C-H键与硫作用的理解。作用于tRNA的甲硫基转移酶的首次X射线晶体结构
Numerous post-transcriptional modifications of transfer RNAs (tRNAs) play vital roles in translation. The 2-methylthio-N6-isopentenyladenosine (ms2i6A) modification occurs at position 37 (A37) in tRNAs that contain adenine in position 36 of the anticodon, and serves to promote efficient A:U codon-anticodon base-pairing and to prevent unintended base-pairing by near cognates, thus enhancing translational fidelity. The ms2i6A modification is installed onto isopentenyladenosine (i6A) by MiaB, a radical S-adenosylmethionine (SAM) methylthiotransferase (MTTase). As a radical SAM protein, MiaB contains one [Fe4S4]RS cluster used in the reductive cleavage of SAM to form a 5’-deoxyadenosyl 5’-radical (5’-dA•), which is responsible for removing the C2 hydrogen of the substrate. MiaB also contains an auxiliary [Fe4S4]aux cluster, which has been implicated in sulfur transfer to C2 of i6A37. How this transfer takes place is largely unknown. Herein, we present several structures of MiaB from Bacteroides uniformis (BuMiaB). These structures are consistent with a two-step mechanism, in which one molecule of SAM is first used to methylate a bridging μ-sulfido ion of the auxiliary cluster. In the second step, a second SAM molecule is cleaved to a 5’-dA•, which abstracts the C2 hydrogen of the substrate, but after C2 has undergone rehybridization from sp2 to sp3. This work advances our understanding of how enzymes functionalize inert C–H bonds with sulfur. First X-ray crystal structures of a methylthiotransferase that acts on tRNA
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影响因子：
14.9
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