Details

Autor(en) / Beteiligte

• Li, Xianghui
• Fu, Rong
• Lee, Sheeyong
• Krebs, Carsten
• Davidson, Victor L.
• Liu, Aimin

Titel

A Catalytic Di-Heme bis-Fe(IV) Intermediate, Alternative to an Fe(IV)=O Porphyrin Radical

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2008-06, Vol.105 (25), p.8597-8600

Ort / Verlag

United States: National Academy of Sciences

Erscheinungsjahr

2008

Link zum Volltext

Quelle

MEDLINE

Beschreibungen/Notizen

• High-valent iron species are powerful oxidizing agents in chemical and biological catalysis. The best characterized form of an Fe(V) equivalent described in biological systems is the combination of a b-type heme with Fe(IV)=O and a porphyrin or amino acid cation radical (termed Compound I). This work describes an alternative natural mechanism to store two oxidizing equivalents above the ferric state for biological oxidation reactions. MauG is an enzyme that utilizes two covalently bound c-type hemes to catalyze the biosynthesis of the protein-derived cofactor tryptophan tryptophylquinone. Its natural substrate is a monohydroxylated tryptophan residue present in a 119-kDa precursor protein. An EPR-silent di-heme reaction intermediate of MauG was trapped. Mössbauer spectroscopy revealed the presence of two distinct Fe(IV) species. One is consistent with an Fe(IV)=O (ferryl) species (δ = 0.06 mm/s, $\Delta E_{{\rm Q}}=1.70\ {\rm mm/s}$). The other is assigned to an Fe(IV) heme species with two axial ligands from protein (δ = 0.17 mm/s, $\Delta E_{{\rm Q}}=2.54\ {\rm mm/s}$), which has never before been described in nature. This bis-Fe(IV) intermediate is remarkably stable but readily reacts with its native substrate. These findings broaden our views of how proteins can stabilize a highly reactive oxidizing species and the scope of enzyme-catalyzed posttranslational modifications.