title: Pulsed ELDOR spectroscopy measures the distance between the two tyrosyl dadicals in the R2 subunit of the E. coli ribonucleotide reductase.
abstract: Escherichia coli ribonucleotide reductase (RNR) catalyzes the conversion of nucleoside diphosphates (NDPs) to deoxynucleoside diphosphates (dNDPs). This RNR is composed of two homodimeric subunits: R1 and R2. R1 binds the NDPs in the active site, and R2 harbors the essential di-iron tyrosyl radical (Y*) cofactor. In this paper, we used PELDOR, a method that detects weak electron-electron dipolar coupling, to make the first direct measurement of the distance between the two Y*'s on each monomer of R2. In the crystal structure of R2, the Y*'s are reduced to tyrosines, and consequently R2 is inactive. In R2, where the Y*'s assume a well-defined geometry with respect to the protein backbone, the PELDOR method allows measurement of a distance of 33.1 +/- 0.2 A that compares favorably to the distance (32.4 A) between the center of mass of the spin density distribution of each Y* on each R2 monomer from the structure. The experiments provide the first direct experimental evidence for two Y*'s in a single R2 in solution.
authors.affiliation: Institute of Physical and Theoretical Chemistry, J. Goethe University of Frankfurt, D-60439 Frankfurt, Germany.
authors.forename: Marina
authors.initials: M
authors.lastname: Bennati
authors.forename: Axel
authors.initials: A
authors.lastname: Weber
authors.forename: Jelena
authors.initials: J
authors.lastname: Antonic
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Perlstein
authors.forename: John
authors.initials: J
authors.lastname: Robblee
authors.forename: JoAnne
authors.initials: J
authors.lastname: Stubbe
mesh_terms: D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004926:Escherichia coli / Q000201:enzymology*; D005609:Free Radicals / Q000737:chemistry; D012264:Ribonucleotide Reductases / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D014443:Tyrosine; D012264:Ribonucleotide Reductases