3hsu | pdb_00003hsu
Functional roles of the 6-s-cysteinyl, 8 alpha-N1-histidyl FAD in Glucooligosaccharide Oxidase from Acremonium strictum
Structural highlights
FunctionGOOX_SARSR Catalyzes the selective oxidation of C1 hydroxyl moieties on mono- and disaccharides with concomitant reduction of molecular oxygen to hydrogen peroxide. This results in the formation of the corresponding lactones, which typically undergo spontaneous hydrolysis. Glucooligosaccharide oxidase is able to oxidize the monosaccharide D-glucose as well as the disaccharides maltose, cellobiose, and lactose. In addition, it shows high selectivity for cello- and maltooligosaccharides, indicating that glucooligosaccharide oxidase prefers oligosaccharides with a beta-D-glucosyl unit on the reducing end and additional sugar units linked by alpha- or beta-1,4 glucosidic bonds.[1] [2] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe crystal structure of glucooligosaccharide oxidase from Acremonium strictum was demonstrated to contain a bicovalent flavinylation, with the 6- and 8alpha-positions of the flavin isoalloxazine ring cross-linked to Cys(130) and His(70), respectively. The H70A and C130A single mutants still retain the covalent FAD, indicating that flavinylation at these two residues is independent. Both mutants exhibit a decreased midpoint potential of approximately +69 and +61 mV, respectively, compared with +126 mV for the wild type, and possess lower activities with k(cat) values reduced to approximately 2 and 5%, and the flavin reduction rate reduced to 0.6 and 14%. This indicates that both covalent linkages increase the flavin redox potential and alter the redox properties to promote catalytic efficiency. In addition, the isolated H70A/C130A double mutant does not contain FAD, and addition of exogenous FAD was not able to restore any detectable activity. This demonstrates that the covalent attachment is essential for the binding of the oxidized cofactor. Furthermore, the crystal structure of the C130A mutant displays conformational changes in several cofactor and substrate-interacting residues and hence provides direct evidence for novel functions of flavinylation in assistance of cofactor and substrate binding. Finally, the wild-type enzyme is more heat and guanidine HCl-resistant than the mutants. Therefore, the bicovalent flavin linkage not only tunes the redox potential and contributes to cofactor and substrate binding but also increases structural stability. Functional roles of the 6-S-cysteinyl, 8alpha-N1-histidyl FAD in glucooligosaccharide oxidase from Acremonium strictum.,Huang CH, Winkler A, Chen CL, Lai WL, Tsai YC, Macheroux P, Liaw SH J Biol Chem. 2008 Nov 7;283(45):30990-6. Epub 2008 Sep 3. PMID:18768475[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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