期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2011
卷号：108
期号：52
页码：21046-21051
DOI：10.1073/pnas.1112715108
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Essential for DNA biosynthesis and repair, ribonucleotide reductases (RNRs) convert ribonucleotides to deoxyribonucleotides via radical-based chemistry. Although long known that allosteric regulation of RNR activity is vital for cell health, the molecular basis of this regulation has been enigmatic, largely due to a lack of structural information about how the catalytic subunit (2) and the radical-generation subunit ({beta}2) interact. Here we present the first structure of a complex between 2 and {beta}2 subunits for the prototypic RNR from Escherichia coli. Using four techniques (small-angle X-ray scattering, X-ray crystallography, electron microscopy, and analytical ultracentrifugation), we describe an unprecedented 4{beta}4 ring-like structure in the presence of the negative activity effector dATP and provide structural support for an active 2{beta}2 configuration. We demonstrate that, under physiological conditions, E. coli RNR exists as a mixture of transient 2{beta}2 and 4{beta}4 species whose distributions are modulated by allosteric effectors. We further show that this interconversion between 2{beta}2 and 4{beta}4 entails dramatic subunit rearrangements, providing a stunning molecular explanation for the allosteric regulation of RNR activity in E. coli.
