Epoxyqueuosine Reductase Structure Suggests a Mechanism for Cobalamin-dependent tRNA Modification.
Epoxyqueuosine Reductase Structure Suggests a Mechanism for Cobalamin-dependent tRNA Modification.
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环氧二糖苷还原酶结构提出了钴胺素依赖性tRNA修饰的机制。
DOI：
10.1074/jbc.m115.685693
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发表时间：
2015-11-13
期刊：
影响因子：
--
通讯作者：
Leys D
中科院分区：
文献类型：
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作者：
Payne KA;Fisher K;Sjuts H;Dunstan MS;Bellina B;Johannissen L;Barran P;Hay S;Rigby SE;Leys D
背景：环氧queue - osine reductase （QueG）催化queue - osine生物合成的最后一步，目前对它知之甚少。结果：我们报道了嗜热链球菌QueG的溶液和结构特征。结论：QueG与还原脱卤酶的相似性主要局限于辅因子结合。意义：我们的研究建立了钴胺代谢与tRNA修饰之间的联系，并提出了钴胺依赖性环氧化物还原的机制。Queuosine (Q)是一种超修饰的RNA碱基，取代了5 ' -GUN-3 ' tRNA分子摆动位置上的鸟嘌呤。Q完全由细菌产生，相应的排队碱基是真核生物抢救的微量营养素。Q生物合成的最后一步是还原环氧化物前体环氧基喹啉，生成Q环戊烯环。环氧基喹啉还原酶QueG与钴胺依赖的还原脱卤酶（RdhA）具有遥远的同源性，然而钴胺素在QueG催化中所起的作用仍然难以捉摸。我们报道了嗜热链球菌QueG的溶液和结构表征，揭示了该酶含有一个由两个[4Fe-4S]簇和一个碱基形式的cob(II)alamin组成的氧化还原链，类似于RdhAs。与共享的氧化还原链结构相反，QueG活性位点与RdhA几乎没有同源性，除了一个保守的Tyr，该Tyr被认为在还原脱卤过程中充当质子供体。环氧基喹啉底物的对接表明QueG活性位点使底物环戊烷部分靠近钴。Tyr和保守的Asp都被认为是环氧化物离去基的质子供体。这表明，与RdhAs催化的不寻常的碳-卤素键化学相反，QueG通过Co-C键形成起作用。我们的研究建立了III类钴胺依赖酶的共同特征，并揭示了这些酶催化的还原化学的意想不到的多样性。
Background: Little is known about epoxyqueuosine reductase (QueG), which catalyzes the final step in the biosynthesis of queuosine. Results: We report solution and structural characterization of Streptococcus thermophilus QueG. Conclusion: The QueG similarity to reductive dehalogenases is largely limited to cofactor binding. Significance: Our study establishes the link between cobalamin-metabolism and tRNA modification and suggests a mechanism for cobalamin-dependent epoxide reduction. Queuosine (Q) is a hypermodified RNA base that replaces guanine in the wobble positions of 5′-GUN-3′ tRNA molecules. Q is exclusively made by bacteria, and the corresponding queuine base is a micronutrient salvaged by eukaryotic species. The final step in Q biosynthesis is the reduction of the epoxide precursor, epoxyqueuosine, to yield the Q cyclopentene ring. The epoxyqueuosine reductase responsible, QueG, shares distant homology with the cobalamin-dependent reductive dehalogenase (RdhA), however the role played by cobalamin in QueG catalysis has remained elusive. We report the solution and structural characterization of Streptococcus thermophilus QueG, revealing the enzyme harbors a redox chain consisting of two [4Fe-4S] clusters and a cob(II)alamin in the base-off form, similar to RdhAs. In contrast to the shared redox chain architecture, the QueG active site shares little homology with RdhA, with the notable exception of a conserved Tyr that is proposed to function as a proton donor during reductive dehalogenation. Docking of an epoxyqueuosine substrate suggests the QueG active site places the substrate cyclopentane moiety in close proximity of the cobalt. Both the Tyr and a conserved Asp are implicated as proton donors to the epoxide leaving group. This suggests that, in contrast to the unusual carbon-halogen bond chemistry catalyzed by RdhAs, QueG acts via Co-C bond formation. Our study establishes the common features of Class III cobalamin-dependent enzymes, and reveals an unexpected diversity in the reductive chemistry catalyzed by these enzymes.