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Directed Evolution of a Non‐Heme‐Iron‐Dependent Extradiol Catechol Dioxygenase: Identification of Mutants with Intradiol Oxidative Cleavage Activity
Author(s) -
Schlosrich Janne,
Eley Kirstin L.,
Crowley Patrick J.,
Bugg Timothy D. H.
Publication year - 2006
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.200600296
Subject(s) - catechol , chemistry , heme , dioxygenase , stereochemistry , mutant , cofactor , biochemistry , enzyme , gene
The non‐heme‐iron(II)‐dependent extradiol catechol dioxygenases catalyse the oxidative cleavage of substituted catechols found on bacterial aromatic degradation pathways. The reaction mechanism of the extradiol dioxygenases is believed to proceed through the same proximal hydroperoxide intermediate as the iron(III)‐dependent intradiol catechol dioxygenases. Directed evolution was carried out on members of the class III extradiol catechol dioxygenases, by using 1) error‐prone polymerase chain reaction, 2) a primer‐based cross‐over method; the mutant dioxygenases were then screened for their ability to process a range of substituted catechols. Several mutant enzymes were found to show higher activity towards certain substituted catechols, including 4‐chlorocatechol, and higher affinity for the iron(II) cofactor. Two mutants isolated from error‐prone PCR of Escherichia coli MhpB (mutants R215W and K273R) were found to produce a mixture of extradiol and intradiol cleavage products, as detected by GC‐MS and 1 H NMR spectroscopy. The residue corresponding to K273 in protocatechuate 4,5‐dioxygenase (LigAB), Val244, is located approximately 12 Å from the iron(II) centre, but close to the putative dioxygen channel; R215 is found on a sequence loop not present in LigB.