Catalytic halogen bonds in enzymatic bond breaking and making in DNA

有了这个奖项，化学部门的生命过程化学项目资助了科罗拉多州立大学的教授Pui S. Ho和Anthony K. rapp<s:1>，以确定卤素如何在设计催化蛋白（酶）中取代镁，从而破坏和形成DNA中的键。镁是酶通常用来帮助切割或连接细胞DNA的金属。何博士的研究小组已经证明，在老鼠体内发现的一种酶中的催化镁可以被一种非天然的氯化或碘化氨基酸取代。这个项目将确定一种叫做卤素键的相互作用是如何允许元素周期表两端的元素催化相同的dna修饰反应的。这门科学探索使用卤素键作为设计工具来设计用于生物技术应用的合成酶的想法。该项目将为研究生和本科生提供结构和计算化学方面的培训，包括那些来自代表性不足群体的学生。最后，一个拓展项目将帮助初高中学生了解科学家如何使用“x射线视觉”在DNA和蛋白质中三维地看到原子。沿DNA主干键的形成和断裂是广泛的基因组过程中的关键反应。内切酶和连接酶通常使用镁离子或类似的金属阳离子作为催化剂来特异性地切割和重新连接DNA片段。Ho和rappase小组已经证明，小鼠内切酶G （mEndoG）中必需的催化二价镁离子可以被氯化或碘化酪氨酸在功能上取代。由此产生的卤化结构再现了野生型mEndoG特异性切割含有5-羟甲基胞嘧啶碱基的四链DNA Holliday连接的活性。这种裂解反应是由氢键（h键）增强卤素键（x键）（简称HBeXB）催化的。此外，该卤化酶还催化了一种独特的不依赖于atp的DNA连接反应，这种反应也见于野生型mEndoG。该研究项目将描述这种无金属、x键催化酶（或cx酶）作为位点特异性核酸内切酶和atp独立连接酶的结构和机制特性。从广泛的科学角度来看，这项工作提出了一种有趣的可能性，即人们可能能够利用x键作为一种新方法来促进酶活性位点的特定催化化学。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With this award, the Chemistry of Life Processes Program of the Chemistry Division is funding Professors Pui S. Ho and Anthony K. Rappé at Colorado State University to determine how halogens can replace magnesium in the design of catalytic proteins (enzymes) that break and make the bonds in DNA. Magnesium is the metal typically used by enzymes to help cut or join DNA in cells. Dr. Ho’s group has shown that the catalytic magnesium in an enzyme found in mice can be replaced by an unnatural chlorinated or iodinated amino acid. This project will determine how an interaction called halogen-bonding allows elements on opposite ends of the periodic table to catalyze the same DNA-modifying reactions. This science probes the idea of using halogen-bonding as a design tool to engineer synthetic enzymes for biotechnology applications. This project will provide training in structural and computational chemistry to graduate and undergraduate students, including those from underrepresented groups. Finally, an outreach project will help middle school and high school students learn how scientists use “X-ray vision” see the atoms in three dimensions in DNA and proteins.The making and breaking of the bonds along the DNA backbone are critical reactions in a broad range of genomic processes. Endonucleases and ligases typically use magnesium ion or similar metal cations as catalysts to specifically cut and rejoin DNA fragments. The Ho and Rappé groups have shown that the essential catalytic divalent magnesium ion in mouse endonuclease G (mEndoG) can be functionally replaced by a chlorinated or iodinated tyrosine. The resulting halogenated construct recapitulates the activity of the wild type mEndoG to specifically cleave four-stranded DNA Holliday junctions that contain a 5-hydroxymethylcytosine base. This cleavage reaction is catalyzed by a hydrogen bond (H-bond) enhanced halogen bond (X-bond), or HBeXB, for short. In addition, the halogenated enzyme was found to catalyze a unique ATP-independent DNA joining reaction that is also seen in the wild type mEndoG. This research project will characterize the structural and mechanistic properties that allow this metal-free, X-bond catalyzed enzyme (or cX-Zyme) to act as a site-specific endonuclease and an ATP-independent ligase. From a broad scientific perspective, this work raises the interesting possibility that one may be able to exploit X-bonding quite generally as a novel method to promote specific catalytic chemistry in enzyme active sites.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.