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Catalytic Site Atlas

CSA LITERATURE entry for 1naa

E.C. namecellobiose dehydrogenase (acceptor)
SpeciesPhanerochaete chrysosporium ()
E.C. Number (IntEnz) 1.1.99.18
CSA Homologues of 1naa1kdg,
CSA Entries With UniProtID Q01738
CSA Entries With EC Number 1.1.99.18
PDBe Entry 1naa
PDBSum Entry 1naa
MACiE Entry 1naa

Literature Report

IntroductionThe oxidoreductase cellobiose dehydrogenase (CDH) from the white-rot fungus Phanerochaete chrysosporium degrades both lignin and cellulose. It catalyses the oxidation of cellobiose (a reaction product in cellulose hydrolysis) to cellobiono-1,5-lactone. This is used to provide a carbon source for the micro-organism. CDH is the only known extracellular flavocytochrome, a small and heterogeneous group of redox-active proteins that carry both haem and flavin prosthetic groups. Applications of CDH include degradation of various environmental pollutants.
MechansimThe generally agreed on mechanism for this reaction is that of the hydride transfer:
1. His 689 acts as a general base by deprotonating the C1 hydroxyl group of the cellobiose substrate, causing hydride transfer from C1 of the substrate to FAD. 2. Asn 732, by hydrogen bonding to O1 of the substrate, facilitates proton transfer to His 689. 3. Tyr 609 hydrogen bonds to a water molecule, increasing the water's affinity for protons, and causing it to deprotonate His 689. 4. This now leaves a reduced FAD (FADH2), the second proton most likely coming from a water molecule.
The mechanism for the oxidation of FADH2 is speculated to be as follows:
1. An internal electron transfer takes place, passing one electron from the flavin centre to the haem, reducing the haem group, and forming a flavin semiquinone. 2. The reduced haem is oxidised by either Fe3+ (to form Fe2+) or superoxide O2- radical (to form hydrogen peroxide.) 3. The semiquinone reacts with O2 to form the O2- radical, and returns to its initial oxidised state.
Ferrous iron can then be oxidised by hydrogen peroxide to re-form Fe3+, and also OH- and an OH radical.
Reaction

Catalytic Sites for 1naa

Annotated By Reference To The Literature - Site 3 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AsnA732750macie:sideChainHydrogen bonds to O1 of the substrate, facilitating proton transfer to His 689.
TyrA609627macie:sideChainHydrogen bonds to a water molecule, causing that water molecule to deprotonate the protonated His 689 residue.
HisA689707macie:sideChainActs as a general base by deprotonating the C1 hydroxyl group, causing hydride transfer to FAD.

Annotated By Reference To The Literature - Site 4 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AsnB732750macie:sideChainHydrogen bonds to O1 of the substrate, facilitating proton transfer to His 689.
TyrB609627macie:sideChainHydrogen bonds to a water molecule, causing that water molecule to deprotonate the protonated His 689 residue.
HisB689707macie:sideChainActs as a general base by deprotonating the C1 hydroxyl group, causing hydride transfer to FAD.

Literature References

Notes:This is not a definite mechanism, it is merely the most agreed upon.
Hallberg BM
Mechanism of the reductive half-reaction in cellobiose dehydrogenase.
J Biol Chem 2003 278 7160-7166
PubMed: 12493734
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