O2- and α-Ketoglutarate-Dependent Tyrosyl Radical Formation in TauD, an α-Keto Acid-Dependent Non-Heme Iron Dioxygenase
| Autor: | Robert P. Hausinger, Lawrence Que, Kevin D. Koehntop, Aimin Liu, Rajendra Bose Muthukumaran, Matthew J. Ryle, Raymond Y. N. Ho, John McCracken |
|---|---|
| Rok vydání: | 2003 |
| Předmět: |
Taurine
Oxygenase Time Factors Free Radicals Iron Spectrum Analysis Raman Photochemistry Biochemistry Medicinal chemistry Mixed Function Oxygenases law.invention chemistry.chemical_compound Reaction rate constant Sulfite Dioxygenase law Serine Ferrous Compounds Enzyme Inhibitors Isoleucine Electron paramagnetic resonance Oxidative decarboxylation Electron Spin Resonance Spectroscopy Chromophore Recombinant Proteins Oxygen Amino Acid Substitution chemistry Spectrophotometry Mutagenesis Site-Directed Oxygenases Ketoglutaric Acids Tyrosine |
| Zdroj: | Biochemistry. 42:1854-1862 |
| ISSN: | 1520-4995 0006-2960 |
| DOI: | 10.1021/bi026832m |
| Popis: | Taurine/alpha-ketoglutarate dioxygenase (TauD), a non-heme mononuclear Fe(II) oxygenase, liberates sulfite from taurine in a reaction that requires the oxidative decarboxylation of alpha-ketoglutarate (alphaKG). The lilac-colored alphaKG-Fe(II)TauD complex (lambda(max) = 530 nm; epsilon(530) = 140 M(-)(1) x cm(-)(1)) reacts with O(2) in the absence of added taurine to generate a transient yellow species (lambda(max) = 408 nm, minimum of 1,600 M(-)(1) x cm(-)(1)), with apparent first-order rate constants for formation and decay of approximately 0.25 s(-)(1) and approximately 0.5 min(-)(1), that transforms to yield a greenish brown chromophore (lambda(max) = 550 nm, 700 M(-)(1) x cm(-)(1)). The latter feature exhibits resonance Raman vibrations consistent with an Fe(III) catecholate species presumed to arise from enzymatic self-hydroxylation of a tyrosine residue. Significantly, (18)O labeling studies reveal that the added oxygen atom derives from solvent rather than from O(2). The transient yellow species, identified as a tyrosyl radical on the basis of EPR studies, is formed after alphaKG decomposition. Substitution of two active site tyrosine residues (Tyr73 and Tyr256) by site-directed mutagenesis identified Tyr73 as the likely site of formation of both the tyrosyl radical and the catechol-associated chromophore. The involvement of the tyrosyl radical in catalysis is excluded on the basis of the observed activity of the enzyme variants. We suggest that the Fe(IV) oxo species generally proposed (but not yet observed) as an intermediate for this family of enzymes reacts with Tyr73 when substrate is absent to generate Fe(III) hydroxide (capable of exchanging with solvent) and the tyrosyl radical, with the latter species participating in a multistep TauD self-hydroxylation reaction. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|