A coupled dinuclear iron cluster that is perturbed by substrate binding in myo-inositol oxygenase.
myo-Inositol oxygenase (MIOX) uses iron as its cofactor and dioxygen as its cosubstrate to effect the unique, ring-cleaving, four-electron oxidation of its cyclohexan-(1,2,3,4,5,6-hexa)-ol substrate to d-glucuronate. The nature of the iron cofactor and its interaction with the substrate, myo-inositol (MI), have been probed by electron paramagnetic resonance (EPR) and Mössbauer spectroscopies. The data demonstrate the formation of an antiferromagnetically coupled, high-spin diiron(III/III) cluster upon treatment of solutions of Fe(II) and MIOX with excess O(2) or H(2)O(2) and the formation of an antiferromagnetically coupled, valence-localized, high-spin diiron(II/III) cluster upon treatment with either limiting O(2) or excess O(2) in the presence of a mild reductant (e.g., ascorbate). Marked changes to the spectra of both redox forms upon addition of MI and analogy to changes induced by binding of phosphate to the diiron(II/III) cluster of the protein phosphatase, uteroferrin, suggest that MI coordinates directly to the diiron cluster, most likely in a bridging mode. The addition of MIOX to the growing family of non-heme diiron oxygenases expands the catalytic range of the family beyond the two-electron oxidation (hydroxylation and dehydrogenation) reactions catalyzed by its more extensively studied members such as methane monooxygenase and stearoyl acyl carrier protein Delta(9)-desaturase.
Xing
Gang
G
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Hoffart
Lee M
LM
Diao
Yinghui
Y
Prabhu
K Sandeep
KS
Arner
Ryan J
RJ
Reddy
C Channa
CC
Krebs
Carsten
C
Bollinger
J Martin
JM
D000818:Animals; D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry; D007294:Inositol / Q000737:chemistry*; D050562:Inositol Oxygenase / Q000737:chemistry*; D007668:Kidney / Q000201:enzymology; D051379:Mice; D010100:Oxygen / Q000737:chemistry*; D011485:Protein Binding; D015204:Spectroscopy, Mossbauer
D005290:Ferric Compounds; D005296:Ferrous Compounds; D007294:Inositol; D050562:Inositol Oxygenase; D010100:Oxygen