Back to Search
Start Over
The role of double covalent flavin binding in chito-oligosaccharide oxidase from Fusarium graminearum
- Source :
- Biochemical Journal, 413(1), 175-183. PORTLAND PRESS LTD
- Publication Year :
- 2008
- Publisher :
- Portland Press Ltd., 2008.
-
Abstract
- ChitO (chito-oligosaccharide oxidase) from Fusarium graminearum catalyses the regioselective oxidation of N-acetylated oligosaccharides. The enzyme harbours an FAD cofactor that is covalently attached to His(94) and Cys(154). The functional role of this unusual bi-covalent flavin-protein linkage was studied by site-directed mutagenesis. The double mutant (H94A/C154A) was not expressed, which suggests that a covalent flavin-protein bond is needed for protein stability. The single mutants H94A and C154A were expressed as FAD-containing enzymes in which one of the covalent FAD-protein bonds was disrupted relative to the wild-type enzyme. Both mutants were poorly active, as the k(cat) decreased (8.3- and 3-fold respectively) and the K-m increased drastically (34- and 75-fold respectively) when using GlcNac as the substrate. Pre-steady-state analysis revealed that the rate of reduction in the mutant enzymes is decreased by 3 orders of magnitude when compared with wild-type ChitO (k(red) = 750 s(-1)) and thereby limits the turnover rate. Spectroelectrochemical titrations revealed that wild-type ChitO exhibits a relatively high redox potential (+ 131 mV) and the C154A mutant displays a lower potential (+ 70 mV), while the H94A mutant displays a relatively high potential of approximately + 164 mV. The results show that a high redox potential is not the only prerequisite to ensure efficient catalysis and that removal of either of the covalent bonds may perturb the geometry of the Michaelis complex. Besides tuning the redox properties, the bi-covalent binding of the FAD cofactor in ChitO is essential for a catalytically competent conformation of the active site.
- Subjects :
- Models, Molecular
ENZYME
Vanillyl-alcohol oxidase
Stereochemistry
TRIMETHYLAMINE DEHYDROGENASE
Molecular Sequence Data
Hexose oxidase
Chitin
Flavin group
Biochemistry
Cofactor
redox potential
Fusarium
oligosaccharides
HEXOSE OXIDASE
Oxidoreductase
Flavins
Gene Expression Regulation, Fungal
GLUCOOLIGOSACCHARIDE OXIDASE
OXIDOREDUCTASE
Amino Acid Sequence
ATTACHED FAD
Molecular Biology
pre-steady-state kinetics
chemistry.chemical_classification
Oxidase test
MOLECULAR-CLONING
PURIFICATION
biology
Chemistry
oxidase
CHONDRUS-CRISPUS
Active site
Cell Biology
Kinetics
bi-covalent FAD
VANILLYL-ALCOHOL OXIDASE
Covalent bond
Mutagenesis, Site-Directed
biology.protein
Carbohydrate Dehydrogenases
Oxidation-Reduction
Subjects
Details
- ISSN :
- 14708728 and 02646021
- Volume :
- 413
- Database :
- OpenAIRE
- Journal :
- Biochemical Journal
- Accession number :
- edsair.doi.dedup.....89421012e8814d41dbf0281c6efb045c