title: Structure of the high-valent FeIIIFeIV state in ribonucleotide reductase (RNR) of Chlamydia trachomatis--combined EPR, 57Fe-, 1H-ENDOR and X-ray studies.
abstract: A recently discovered subgroup of class I ribonucleotide reductase (RNR) found in the infectious bacterium Chlamydia trachomatis (C. trachomatis) was shown to exhibit a high-valent Fe(III)Fe(IV) center instead of the tyrosyl radical observed normally in all class I RNRs. The X-ray structure showed that C. trachomatis WT RNR has a phenylalanine at the position of the active tyrosine in Escherichia coli RNR. In this paper the X-ray structure of variant F127Y is presented, where the tyrosine is restored. Using (1)H- and (57)Fe-ENDOR spectroscopy it is shown, that in WT and variants F127Y and Y129F of C. trachomatis RNR, the Fe(III)Fe(IV) center is virtually identical with the short-lived intermediate X observed during the iron oxygen reconstitution reaction in class I RNR from E. coli. The experimental data are consistent with a recent theoretical model for X, proposing two bridging oxo ligands and one terminal water ligand. A surprising extension of the lifetime of the Fe(III)Fe(IV) state in C. trachomatis from a few seconds to several hours at room temperature was observed under catalytic conditions in the presence of substrate. These findings suggest a possible new role for the Fe(III)Fe(IV) state also in other class I RNR, during the catalytic radical transfer reaction, by which the substrate turnover is started.
authors.affiliation: Department of Biochemistry and Biophysics, Stockholm University, S-10691 Stockholm, Sweden.
authors.forename: Nina
authors.initials: N
authors.lastname: Voevodskaya
authors.forename: Marcus
authors.initials: M
authors.lastname: Galander
authors.forename: Martin
authors.initials: M
authors.lastname: Högbom
authors.forename: Pal
authors.initials: P
authors.lastname: Stenmark
authors.forename: Grant
authors.initials: G
authors.lastname: McClarty
authors.forename: Astrid
authors.initials: A
authors.lastname: Gräslund
authors.forename: Friedhelm
authors.initials: F
authors.lastname: Lendzian
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D002692:Chlamydia trachomatis / Q000201:enzymology* / Q000235:genetics; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D017354:Point Mutation; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000235:genetics; D013379:Substrate Specificity / Q000235:genetics