Flavivirus RNA cap methyltransferase: structure, function, and inhibition.
Flavivirus RNA cap methyltransferase: structure, function, and inhibition.
复制标题
DOI：
10.1007/s11515-010-0660-y
复制
发表时间：
2010-08-01
期刊：
影响因子：
--
通讯作者：
中科院分区：
文献类型：
--
作者：
许多黄病毒是重要的人类病原体。黄病毒的正链RNA基因组包含一个5′端帽1结构（m7GpppAmG）。黄病毒编码一种甲基转移酶（MTase），位于NS5 RNA依赖的RNA聚合酶（RdRp）的N端部分。在此我们综述在我们对黄病毒加帽机制的理解以及对药物开发的影响方面的最新进展。NS5甲基转移酶在病毒帽形成过程中催化鸟嘌呤N7和核糖2′ - OH的甲基化。来自登革热、黄热病和西尼罗河病毒（WNV）的代表性黄病毒甲基转移酶依次产生GpppA→m7GpppA→m7GpppAm。尽管存在两种不同的甲基化活性，但黄病毒甲基转移酶的晶体结构显示出一个用于S - 腺苷 - L - 甲硫氨酸（SAM）（甲基供体）的单一结合位点。这一发现表明在连续反应过程中，底物GpppA - RNA必须重新定位以从SAM接受N7和2′ - O甲基。进一步的研究表明，帽上鸟嘌呤N7的甲基化和第一个转录核苷酸上核糖2′ - OH的甲基化需要不同的RNA元件。具有不同甲基化缺陷的突变酶在体外可以相互反式互补，表明该酶的独立分子在体外可以独立催化两种帽甲基化。在感染性病毒的情况下，两种甲基化的缺陷，或者单独N7甲基化的缺陷，对西尼罗河病毒是致命的。然而，仅在2′ - O甲基化有缺陷的病毒是减毒的，并且可以保护小鼠免受后续野生型西尼罗河病毒的攻击。这些结果表明N7甲基化活性对西尼罗河病毒的生命周期是必不可少的，因此，甲基转移酶代表了黄病毒治疗的一个新的且有前景的靶点。
Many flaviviruses are significant human pathogens. The plus-strand RNA genome of a flavivirus contains a 5′ terminal cap 1 structure (m7GpppAmG). The flavivirus encodes one methyltransferase (MTase), located at the N-terminal portion of the NS5 RNA-dependent RNA polymerase (RdRp). Here we review recent advances in our understanding of flaviviral capping machinery and the implications for drug development. The NS5 MTase catalyzes both guanine N7 and ribose 2′-OH methylations during viral cap formation. Representative flavivirus MTases, from dengue, yellow fever, and West Nile virus (WNV), sequentially generate GpppA → m7GpppA → m7GpppAm. Despite the existence of two distinct methylation activities, the crystal structures of flavivirus MTases showed a single binding site for S-adenosyl-L-methionine (SAM), the methyl donor. This finding indicates that the substrate GpppA-RNA must be repositioned to accept the N7 and 2′-O methyl groups from SAM during the sequential reactions. Further studies demonstrated that distinct RNA elements are required for the methylations of guanine N7 on the cap and of ribose 2′-OH on the first transcribed nucleotide. Mutant enzymes with different methylation defects can trans complement one another in vitro, demonstrating that separate molecules of the enzyme can independently catalyze the two cap methylations in vitro. In the context of the infectious virus, defects in both methylations, or a defect in the N7 methylation alone, are lethal to WNV. However, viruses defective solely in 2′-O methylation are attenuated and can protect mice from later wild-type WNV challenge. The results demonstrate that the N7 methylation activity is essential for the WNV life cycle and, thus, methyltransferase represents a novel and promising target for flavivirus therapy.