2rdb
X-ray Crystal Structure of Toluene/o-Xylene Monooxygenase Hydroxylase I100W Mutant
|
OverviewOverview
At its carboxylate-bridged diiron active site, the hydroxylase component, of toluene/o-xylene monooxygenase activates dioxygen for subsequent arene, hydroxylation. In an I100W variant of this enzyme, we characterized the, formation and decay of two species formed by addition of dioxygen to the, reduced, diiron(II) state by rapid-freeze quench (RFQ) EPR, Mossbauer, and, ENDOR spectroscopy. The dependence of the formation and decay rates of, this mixed-valent transient on pH and the presence of phenol, propylene, or acetylene was investigated by double-mixing stopped-flow optical, spectroscopy. Modification of the alpha-subunit of the hydroxylase after, reaction of the reduced protein with dioxygen-saturated buffer was, investigated by tryptic digestion coupled mass spectrometry. From these, investigations, we conclude that (i) a diiron(III,IV)-W* transient, kinetically linked to a preceding diiron(III) intermediate, arises from, the one-electron oxidation of W100, (ii) the tryptophan radical is, deprotonated, (iii) rapid exchange of either a terminal water or hydroxide, ion with water occurs at the ferric ion in the diiron(III,IV) cluster, and, (iv) the diiron(III,IV) core and W* decay to the diiron(III) product by a, common mechanism. No transient radical was observed by stopped-flow, optical spectroscopy for reactions of the reduced hydroxylase variants, I100Y, L208F, and F205W with dioxygen. The absence of such species, and, the deprotonated state of the tryptophanyl radical in the, diiron(III,IV)-W* transient, allow for a conservative estimate of the, reduction potential of the diiron(III) intermediate as lying between 1.1, and 1.3 V. We also describe the X-ray crystal structure of the I100W, variant of ToMOH.
About this StructureAbout this Structure
2RDB is a Protein complex structure of sequences from Pseudomonas stutzeri with , , and as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Dioxygen Activation at Non-Heme Diiron Centers: Oxidation of a Proximal Residue in the I100W Variant of Toluene/o-Xylene Monooxygenase Hydroxylase., Murray LJ, Garcia-Serres R, McCormick MS, Davydov R, Naik SG, Kim SH, Hoffman BM, Huynh BH, Lippard SJ, Biochemistry. 2007 Dec 25;46(51):14795-809. Epub 2007 Nov 29. PMID:18044971
Page seeded by OCA on Wed Jan 23 11:35:32 2008