LONG RANGE RADICAL INITIATION IN E COLI RIBONUCLEOTIDE REDUCTASE

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。 大肠杆菌核糖核苷酸还原酶催化核苷二磷酸(NDP)转化为脱氧核苷二磷酸。活性蛋白由两个同源二聚体亚基(R1和R2)组成，它们被认为形成了1：1的复合体。R1结合NDP底物，容纳催化所需的必需半胱氨酸和控制底物专一性和周转率的变构效应器的结合部位。R2在残基122(Y？)上含有必需的二铁酪氨酸自由基辅因子。一个尚未解决的主要问题是自由基的引发机制：酪氨酰基(Y？)在R2中产生一个瞬时的硫基自由基(C439？)在核苷酸还原所需的R1中。目前的自由基引发过程模型涉及一条特定的电子转移途径，该途径跨越3.5 nm的距离，源于R1和R2结构的对接模型，但从现有的结构信息来看，该途径的很大一部分并不明显。为了建立自由基引发模型，必须测量Y122和C439之间的距离。

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. E.coli ribonucleotide reductase catalyzes the conversion of nucleoside diphosphates (NDP) to deoxynucleoside diphosphates. The active protein is composed of two homodimeric subunits (R1 and R2) thought to form a 1:1 complex. R1 binds the NDP substrates, houses the essential cysteines required for catalysis and the binding sites for the allosteric effectors that govern substrate specificity and turnover rates. R2 harbors the essential di-iron tyrosyl radical cofactor on residue 122 (Y?). A major unresolved issue is the mechanism of radical initiation: how the tyrosyl radical (Y?) in R2 generates a transient thiyl radical (C439?) in R1 required for nucleotide reduction. The current model for the radical initiation process involves a specific electron transfer pathway, which traverses a distance of 3.5 nm, derived from a docking model of the R1 and R2 structures, but a substantial part of the pathway is not apparent from the available structural information. A measurement of the distance between Y122 and C439 was imperative to establish the radical initiation model.