Oxidative inactivation of ring-cleavage extradiol dioxygenases : mechanism and ferredoxin-mediated reactivation

Yves Jouanneau (1)

1 LCBM - UMR 5249 - Laboratoire de Chimie et Biologie des Métaux

Extradiol dioxygenases are ubiquitous enzymes that catalyze ring cleavage of a wide variety of aromatic compounds. Most of these enzymes contain a ferrous ion at the active site, which is bound to the polypeptide chain through a conserved triad of two histidines and one glutamic acid. During the catalytic cycle, a catecholic substrate first binds at the active site, followed by dioxygen and the ternary complex formed yields a bound superoxide that attacks the substrate, leading eventually to ring cleavage. The active site iron remains ferrous during catalysis, except when poor substrates such as chloro- or methylcatechols are processed. In such cases, the enzyme becomes inactivated through oxidation and eventually loss of its active site iron atom. In Pseudomonas putida mt-2, catechol 2,3-dioxygenase, which is involved in toluene degradation, is inactivated by 4-methylcatechol. The enzyme is however rescued by a specific reactivation system involving a [2Fe-2S] ferredoxin encoded by xylT. The role of this ferredoxin is to reduce the ferric ion of the inactive enzyme thereby regenerating the active catalyst. Recent findings indicate that the electrons needed for the XylT-mediated reactivation are provided by XylZ, a NADH-oxidoreductase that is part of the toluate dioxygenase complex. XylT analogues present in other bacteria have been shown to have a similar role in the reactivation of catechol dioxygenases involved in the degradation of various aromatic hydrocarbons including cresols, chlorobenzene and naphthalene. The occurrence and significance of ferredoxin-mediated extradiol dioxygenae repair systems in bacteria is discussed.

Mots clés: dioxygenase; aromatic ring cleavage; suicide inactivation; ferredoxin

Domaines: Biochimie [q-bio.BM]

Yves Jouanneau. Oxidative inactivation of ring-cleavage extradiol dioxygenases : mechanism and ferredoxin-mediated reactivation. K. N. Timmis. Microbiology of hydrocarbons, oils, lipids, and derived compounds, Springer, in press, 2009. ⟨hal-00379799⟩