title: Re(bpy)(CO)3CN as a probe of conformational flexibility in a photochemical ribonucleotide reductase.
abstract: Photochemical ribonucleotide reductases (photoRNRs) have been developed to study the proton-coupled electron transfer (PCET) mechanism of radical transport in Escherichia coli class I ribonucleotide reductase (RNR). The transport of the effective radical occurs along several conserved aromatic residues across two subunits: beta2((*)Y122 --> W48 --> Y356) --> alpha2(Y731 --> Y730 --> C439). The current model for RNR activity suggests that radical transport is strongly controlled by conformational gating. The C-terminal tail peptide (Y-betaC19) of beta2 is the binding determinant of beta2 to alpha2 and contains the redox active Y356 residue. A photoRNR has been generated synthetically by appending a Re(bpy)(CO)(3)CN ([Re]) photo-oxidant next to Y356 of the 20-mer peptide. Emission from the [Re] center dramatically increases upon peptide binding, serving as a probe for conformational dynamics and the protonation state of Y356. The diffusion coefficient of [Re]-Y-betaC19 has been measured (k(d1) = 6.1 x 10(-7) cm(-1) s(-1)), along with the dissociation rate constant for the [Re]-Y-betaC19-alpha2 complex (7000 s(-1) > k(off) > 400 s(-1)). Results from detailed time-resolved emission and absorption spectroscopy reveal biexponential kinetics, suggesting a large degree of conformational flexibility in the [Re]-Y-betaC19-alpha2 complex that engenders partitioning of the N-terminus of the peptide into both bound and solvent-exposed fractions.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology,77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA.
authors.forename: Steven Y
authors.initials: SY
authors.lastname: Reece
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Lutterman
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Seyedsayamdost
authors.forename: JoAnne
authors.initials: J
authors.lastname: Stubbe
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Nocera
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism; D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism; D003486:Cyanides / Q000737:chemistry* / Q000378:metabolism; D004579:Electron Transport; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D005609:Free Radicals / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D015335:Molecular Probes / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010777:Photochemistry; D011487:Protein Conformation; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D012211:Rhenium / Q000737:chemistry* / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000378:metabolism; D055672:Static Electricity
chemical_list: D003486:Cyanides; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; D005609:Free Radicals; D008024:Ligands; D015335:Molecular Probes; D015082:2,2'-Dipyridyl; D012211:Rhenium; D002248:Carbon Monoxide; D012264:Ribonucleotide Reductases