STRUCTURE OF THE ACTIVATED OLIGOMER OF THE ALLOSTERIC ENDONUCLEASE SGRAI

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 我们发现SgrAI是一种序列特异性双链核酸内切酶，它能形成DNA结合形式的寡聚体，激活该酶的DNA切割活性，并改变其序列特异性。寡聚作用可以将激活的酶从宿主基因组DNA中隔离出来，也可以迅速激活酶以保护宿主免受噬菌体的入侵。高分辨X射线晶体结构显示了未齐聚形式(DNA结合的酶二聚体)的结构，以及寡聚体的潜在构建块(两个DNA结合的酶二聚体相互关联)的结构。“头对头”相关的DNA结合酶二聚体利用结构域交换来部分稳定这种联系，这是相当不寻常和意想不到的。我们希望用SAXS表征通过与DNA结合而稳定的更大的低聚物，这种结合比晶体结构中使用的DNA更长。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We have discovered that SgrAI, a sequence specific double stranded endonuclease, forms oligomers of the DNA bound form, which activate the enzyme's DNA cleavage activity, and also alter its sequence specificity. The oligomerization may serve to sequester activated enzymes away from the host genomic DNA, and may also serve to rapidly activate the enzyme to protect the host from invading phage. High resolution x-ray crystal structures show the structure of the unoligomerized form (a DNA bound enzyme dimer), and of a potential building block of the oligomer (two DNA bound enzyme dimers associated "head-to-head"). The "head-to-head" associated DNA bound enzyme dimers utilized domain swapping to stabilize, in part, the association, which is quite unusual and unexpected. We hope to characterize, using SAXS, the larger oligomer that is stabilized by binding to DNA that is longer than that used in the crystal structures.