CHARACTERIZATION OF NUCLEOTIDE DEPENDANT OLIOGOMERIC STATES OF RNR1P USING SAXS

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 核糖核苷酸还原酶(RNR)催化合成DNA复制所需的脱氧核糖核酸池中的限速步骤。RNR对细胞的快速增殖至关重要，是抗HSV和抗癌药物的成功靶点。变构调节是RNR活性调节的重要方式之一，目前主要有两种模型来描述RNR的变构行为。Reichard和Thelander提出的模型(RT模型)认为，底物在催化位点(c-位点)的结合受特定位点(S-位点)结合的dNTP控制，而全局酶的活性取决于三磷酸腺苷或dATP与活性位点的结合(Eriksson，Uhlin等人)。1997年)。RT模型的主要缺点之一是它不能解释RNR在亚基异构化背景下的活性。库珀曼最近描述的一个全面的变构模型不仅吸收了RT模型的基本原理，而且定性地描述了核苷酸依赖的寡聚如何调节酶的活性。除了S位点和a位点外，综合模型还描述了Rnr1中的第三个变构位点，称为六聚体位点(h位点)。在生理浓度下，三磷酸腺苷与h-位的结合推动六聚体的形成。在这个模型中，由于四聚体的形成不活跃，dATP被认为是一种通用的抑制剂。在这项建议中，我们希望用小角X射线散射来表征RNR复合体Rnr1亚单位的核苷酸依赖的寡聚化状态。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Ribonucleotide reductase (RNR) catalyzes the rate-limiting step in production of the pool of deoxyribonucleotides necessary for DNA replication. Crucial for rapidly proliferating cells, RNR is a successful target for anti-HSV and anticancer drugs. Allosteric regulation consitutes one of the important modes of regualtion of RNR activity.Currently, there are two major models that describe the allosteric behavior of RNR. The model proposed by Reichard and Thelander (RT model) accounts that the substrate binding at the catalytic site (c-site) is governed by a given dNTP bound to the specificity site (s-site), while global enzyme activity is dependent on either ATP or dATP binding to the activity site(Eriksson, Uhlin et al. 1997). One of the major drawbacks of the RT model is its inability of explaining RNR's activity in the context of subunit olgiomerization. A recently described comprehensive allosteric model by Cooperman not only takes in the basic tenets of the RT model but also qualitatively describes how enzyme activity is regulated by nucleotide dependant oligomerization. In addition to the s- and a-sites, the comprehensive model describes a third allosteric site in Rnr1 known as the hexameric site (h-site). At physiologically significant concentrations, binding of ATP to h-site drives hexamer formation. In this model, dATP is regarded as a universal inhibitor because of inactive tetramer formation. In this proposal we hope to characterize the nucleotide dependant oligomerization state of Rnr1 subunit of the RNR complex using small angle X-ray scattering.