Structure and Specificity of Restriction-Modification (R-M) Systems

限制修饰（R-M）系统包括细菌和古细菌中的先天免疫系统。他们的 50年前由Arber、Nathans和Smith发现（1978年诺贝尔生理学和医学奖） 开启了现代生物技术的大门如果没有R-M酶， DNA革命和没有基因技术，正如我们今天所知道的。R-M系统从简单的II型 酶到需要ATP的更复杂的酶家族（I型和III型）或编码两者的酶 在相同多肽内的核酸内切酶和甲基化活性（IIL型）。我们学到了很多 在过去的二十年里，关于简单的II型酶的结构和机制（如 BamHI和FokI），提供了对极端蛋白质-DNA选择性的基础的基本见解， 有助于产生新的嵌合核酸酶。然而，关于另一个问题， 更复杂的R-M酶家族。EcoP 15 I是III型R-M系列的原型，其功能为 假解旋酶或分子开关，在遥远的DNA位点之间进行通信。DNA被切割 当两个EcoP 15 I复合物碰撞时。虽然Ecop 15 I在40多年前就被发现了， 结构信息。我们已经解析了完整Ecop 15 I复合物的晶体结构。我们将 进行额外的结构和功能研究，旨在了解其易位机制 和DNA切割。MmeI是Type IIL R-M系列的原型，为以下操作提供了天然平台： 设计新的DNA结合特异性。在这方面已经取得了一些成功。我们 将使用MmeI样酶的结构信息来识别特异性决定簇，然后可以 合理突变以产生新的核酸酶。我们还希望了解这些酶是如何控制它们的 核酸酶活性，作为一种防止自我限制的手段，同时允许限制病毒 DNA.总的来说，我们将揭示这些复杂的R-M系统通信的新结构原则 以及特异性决定子如何被塑造成新的 内切酶

Restriction-modification (R-M) systems comprise the innate immune system in bacteria and archaea. Their discovery ~50 years ago by Arber, Nathans, and Smith (1978 Nobel Prize in Physiology & Medicine) opened the doors of modern biotechnology. Without R-M enzymes there would haven been no recombinant DNA revolution and no gene technology, as we know it today. R-M systems range from simple Type II enzymes to more complex families of enzymes that require ATP (Type I and III) or that encode both endonuclease and methylation activities within the same polypeptide (Type IIL). Much has been learned over the past two decades about the structure and mechanism of the simple Type II enzymes (such as BamHI and FokI), providing fundamental insights into the basis of extreme protein-DNA selectivity and lending to the creation of novel chimeric nucleases. However, much remains to be learned about the other more complex families of R-M enzymes. EcoP15I is a prototype of the Type III R-M family that functions as a pseudo-helicase or a molecular switch to communicate between distant DNA sites. The DNA is cleaved when two EcoP15I complexes collide. Although Ecop15I was discovered >40 years ago there had been no structural information. We have resolved the crystal structure of the complete Ecop15I complex. We will carry out additional structural and functional studies aimed at understanding its mechanism of translocation and DNA cleavage. MmeI is a prototype of the Type IIL R-M family that provides a natural platform for engineering new DNA-binding specificities. Some success has already been achieved in this direction. We will use structural information on MmeI-like enzymes to identify specificity determinants, which can then be rationally mutated to generate new nucleases. We also look to understand how these enzymes control their nuclease activity, as a means to prevent self-restriction while at the same time allowing for restriction of viral DNA. Overall, we will uncover new structural principles by which these complex R-M systems communicate and cleave DNA over long distances and how specificity determinants can be molded to create new enzymes.