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J Biol Chem. 2008 May 30;283(22):15209-16. Epub 2008 Mar 24.
Structural and biophysical characterization of human myo-inositol oxygenase.

Thorsell AG, Persson C, Voevodskaya N, Busam RD, Hammarstrom M, Graslund S, Graslund A, Hallberg BM.

Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, SE-171 77 Stockholm, Sweden.

Altered inositol metabolism is implicated in a number of diabetic complications. The first committed step in mammalian inositol catabolism is performed by myo-inositol oxygenase (MIOX), which catalyzes a unique four-electron dioxygen-dependent ring cleavage of myo-inositol to D-glucuronate. Here, we present the crystal structure of human MIOX in complex with myo-inosose-1 bound in a terminal mode to the MIOX diiron cluster site. Furthermore, from biochemical and biophysical results from N-terminal deletion mutagenesis we show that the N terminus is important, through coordination of a set of loops covering the active site, in shielding the active site during catalysis. EPR spectroscopy of the unliganded enzyme displays a two-component spectrum that we can relate to an open and a closed active site conformation. Furthermore, based on site-directed mutagenesis in combination with biochemical and biophysical data, we propose a novel role for Lys(127) in governing access to the diiron cluster.

PMID: 18364358 [PubMed - indexed for MEDLINE]