Vértessy Béata G, Tóth Judit
Institute of Enzymology, Hungarian Academy of Sciences, Budapest, Hungary.
Acc Chem Res. 2009 Jan 20;42(1):97-106. doi: 10.1021/ar800114w.
The thymine-uracil exchange constitutes one of the major chemical differences between DNA and RNA. Although these two bases form the same Watson-Crick base pairs with adenine and are equivalent for both information storage and transmission, uracil incorporation in DNA is usually a mistake that needs to be excised. There are two ways for uracil to appear in DNA: thymine replacement and cytosine deamination. Most DNA polymerases readily incorporate dUMP as well as dTMP depending solely on the availability of the d(U/T)TP building block nucleotides. Cytosine deamination results in mutagenic U:G mismatches that must be excised. The repair system, however, also excises U from U:A "normal" pairs. It is therefore crucial to limit thymine-replacing uracils.dUTP is constantly produced in the pyrimidine biosynthesis network. To prevent uracil incorporation into DNA, representatives of the dUTP nucleotidohydrolase (dUTPase) enzyme family eliminate excess dUTP. This Account describes recent studies that have provided important detailed insights into the structure and function of these essential enzymes.dUTPases typically possess exquisite specificity and display an intriguing homotrimer active site architecture. Conserved residues from all three monomers contribute to each of the three active sites within the dUTPase. Although even dUTPases from evolutionarily distant species possess similar structural and functional traits, in a few cases, a monomer dUTPase mimics the trimer structure through an unusual folding pattern. Catalysis proceeds by way of an SN2 mechanism; a water molecule initiates in-line nucleophilic attack. The dUTPase binding pocket is highly specific for uracil. Phosphate chain coordination involves Mg2+ and is analogous to that of DNA polymerases. Because of conformational changes in the enzyme during catalysis, most crystal structures have not resolved the residues in the C-terminus. However, recent high-resolution structures are beginning to provide in-depth structural information about this region of the protein.The dUTPase family of enzymes also shows promise as novel targets for anticancer and antimicrobial therapies. dUTPase is upregulated in human tumor cells. In addition, dUTPase inhibitors could also fight infectious diseases such as malaria and tuberculosis. In these respective pathogens, Plasmodium falciparum and Mycobacterium tuberculosis, the biosynthesis of dTMP relies exclusively on dUTPase activity.
胸腺嘧啶-尿嘧啶的交换是DNA与RNA之间主要的化学差异之一。尽管这两种碱基与腺嘌呤形成相同的沃森-克里克碱基对，并且在信息存储和传递方面等效，但尿嘧啶掺入DNA通常是一个需要切除的错误。尿嘧啶出现在DNA中有两种方式：胸腺嘧啶替代和胞嘧啶脱氨。大多数DNA聚合酶很容易掺入dUMP以及dTMP，这仅取决于d(U/T)TP构建核苷酸的可用性。胞嘧啶脱氨会导致诱变的U:G错配，必须将其切除。然而，修复系统也会从U:A“正常”碱基对中切除U。因此，限制胸腺嘧啶替代的尿嘧啶至关重要。dUTP在嘧啶生物合成网络中不断产生。为了防止尿嘧啶掺入DNA，dUTP核苷酸水解酶（dUTPase）酶家族的成员会消除过量的dUTP。本综述介绍了最近的研究，这些研究为这些必需酶的结构和功能提供了重要的详细见解。dUTPase通常具有极高的特异性，并呈现出一种有趣的同三聚体活性位点结构。来自所有三个单体的保守残基对dUTPase内的三个活性位点都有贡献。尽管即使是来自进化距离较远物种的dUTPase也具有相似的结构和功能特征，但在少数情况下，单体dUTPase通过一种不寻常的折叠模式模仿三聚体结构。催化通过SN2机制进行；一个水分子引发亲核攻击。dUTPase结合口袋对尿嘧啶具有高度特异性。磷酸链配位涉及Mg²⁺，类似于DNA聚合酶。由于催化过程中酶的构象变化，大多数晶体结构尚未解析C端的残基。然而，最近的高分辨率结构开始提供有关该蛋白质区域的深入结构信息。dUTPase酶家族也有望成为抗癌和抗菌治疗的新靶点。dUTPase在人类肿瘤细胞中上调。此外，dUTPase抑制剂还可以对抗疟疾和结核病等传染病。在这些病原体中，恶性疟原虫和结核分枝杆菌，dTMP的生物合成完全依赖于dUTPase活性。
