Structural and biophysical characterization of human myo-inositol oxygenase.
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.
Thorsell
Ann-Gerd
AG
Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
Persson
Camilla
C
Voevodskaya
Nina
N
Busam
Robert D
RD
Hammarström
Martin
M
Gräslund
Susanne
S
Gräslund
Astrid
A
Hallberg
B Martin
BM
D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D018360:Crystallography, X-Ray; D048909:Diabetes Complications / Q000201:enzymology / Q000235:genetics; D006801:Humans; D007294:Inositol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D050562:Inositol Oxygenase; D016296:Mutagenesis; D010105:Oxygenases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D017384:Sequence Deletion
C002183:inosose; D007294:Inositol; D010105:Oxygenases; D050562:Inositol Oxygenase; C485890:MIOX protein, human