Reece, Steven Y.Lutterman, Daniel A.Seyedsayamdost, MohammadStubbe, JoAnneNocera, Daniel2017-07-182009Reece, Steven Y., Daniel A. Lutterman, Mohammad R. Seyedsayamdost, JoAnne Stubbe, and Daniel G. Nocera. 2009. “Re(bpy)(CO)3CN as a Probe of Conformational Flexibility in a Photochemical Ribonucleotide Reductase.” Biochemistry 48 (25) (June 30): 5832–5838. doi:10.1021/bi9005804.0006-2960http://nrs.harvard.edu/urn-3:HUL.InstRepos:33464243Photochemical ribonucleotide reductases (photoRNRs) have been developed to study the proton-coupled electron transfer (PCET) mechanism of radical transport in class I E. coli ribonucleotide reductase (RNR). The transport of the effective radical occurs along several conserved aromatic residues across two subunits: β2(•Y122→W48→Y356)→ α2(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- βC19) of β2 is the binding determinant of β2 to α2 and contains the redox active Y356 residue. A photoRNR has been generated synthetically by appending a Re(bpy)(CO)3CN ([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 Y356 protonation state. The diffusion coefficient of [Re]-Y-βC19 has been measured (kd1 = 6.1 × 10−7 cm−1 s–1), along with the dissociation rate constant for the [Re]-Y-βC19:α2 complex (7000 s−1 > koff > 400 s−1). Results from detailed time-resolved emission and absorption spectroscopies reveal biexponential kinetics, suggesting a large degree of conformational flexibility in the α2:[Re]-Y-βC19 complex that partitions the N-terminus of the peptide into both bound and solvent-exposed fractions.en-USJournal Article2017-05-1120092017-07-1810.1021/bi9005804