Open AccessChlamydial ribonucleotide reductase: Tyrosyl radical function in catalysis replaced by the Fe III -Fe IV cluster
Author(s) -
Nina Voevodskaya,
A-J Narvaez,
V. D. Domkin,
Eduard Torrents,
Lars Thelander,
Astrid Gräslund
Publication year - 2006
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.0600603103
Subject(s) - ribonucleotide reductase , chemistry , catalysis , catalytic cycle , active site , electron paramagnetic resonance , tyrosine , stereochemistry , turnover number , phenylalanine , ribonucleotide , photochemistry , nucleotide , biochemistry , amino acid , nuclear magnetic resonance , physics , protein subunit , gene
Ribonucleotide reductase (RNR) from Chlamydia trachomatis is a class I RNR composed of proteins R1 and R2. In protein R2, the tyrosine residue harboring the radical that is necessary for catalysis in other class I RNRs is replaced by a phenylalanine. Active C. trachomatis RNR instead uses the Fe(III)-Fe(IV) state of the iron cluster in R2 as an initiator of catalysis. The paramagnetic Fe(III)-Fe(IV) state, identified by (57)Fe substitution, becomes electron spin resonance detectable in samples that are frozen during conditions of ongoing catalysis. Its amount depends on the conditions for catalysis, such as incubation temperature and the R1/R2 ratio. The results link induction of the Fe(III)-Fe(IV) state with enzyme activity of chlamydial RNR. Based on these observations, a reaction scheme is proposed for the iron site. This scheme includes (i) an activation cycle involving reduction and an oxygen reaction in R2 and (ii) a catalysis cycle involving substrate binding and turnover in R1.