title: Structural interconversions modulate activity of Escherichia coli ribonucleotide reductase.
abstract: 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 (α(2)) and the radical-generation subunit (β(2)) interact. Here we present the first structure of a complex between α(2) and β(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 α(4)β(4) ring-like structure in the presence of the negative activity effector dATP and provide structural support for an active α(2)β(2) configuration. We demonstrate that, under physiological conditions, E. coli RNR exists as a mixture of transient α(2)β(2) and α(4)β(4) species whose distributions are modulated by allosteric effectors. We further show that this interconversion between α(2)β(2) and α(4)β(4) entails dramatic subunit rearrangements, providing a stunning molecular explanation for the allosteric regulation of RNR activity in E. coli.
authors.affiliation: Department of Chemistry, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Nozomi
authors.initials: N
authors.lastname: Ando
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Brignole
authors.forename: Christina M
authors.initials: CM
authors.lastname: Zimanyi
authors.forename: Michael A
authors.initials: MA
authors.lastname: Funk
authors.forename: Kenichi
authors.initials: K
authors.lastname: Yokoyama
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Asturias
authors.forename: Joanne
authors.initials: J
authors.lastname: Stubbe
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Drennan
mesh_terms: D000494:Allosteric Regulation / Q000502:physiology; D003460:Crystallization; D018360:Crystallography, X-Ray; D004247:DNA / Q000096:biosynthesis; D004926:Escherichia coli / Q000201:enzymology*; D008854:Microscopy, Electron; D008958:Models, Molecular; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry*; D012264:Ribonucleotide Reductases / Q000737:chemistry*; D014461:Ultracentrifugation
chemical_list: D021122:Protein Subunits; D004247:DNA; D012264:Ribonucleotide Reductases