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Catalytic Site Atlas Version 2.2.12
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CSA entry for 1i19
Original Entry
Title:
Oxidoreductase
Compound:
Cholesterol oxidase
Mutant:
No
UniProt/Swiss-Prot:
Q7SID9-Q7SID9
EC Class:
1.1.3.6
Other CSA Entries:
Overview of all sites for 1i19
Homologues of 1i19
Entries for UniProt/Swiss-Prot: Q7SID9
Entries for EC: 1.1.3.6
Other Databases:
PDB entry: 1i19
PDBsum entry: 1i19
UniProt/Swiss-Prot: Q7SID9
IntEnz entry: 1.1.3.6
Literature Report:
Introduction:
Cholesterol oxidase catalyses the oxidation and isomerisation of cholesterol to form cholest-4-en-3-one using FAD as a cofactor. The two forms of the enzyme found in Brevibacterium BCO1 and BCO2 do not show any structural or sequence homology, despite carrying out the same reaction. As a result their mechanisms are believed to be different. Study of the enzymes that degrade cholesterol is clearly of great relevance to medicine due to the role of the steroid in cardiovascular disease.
Mechanism:
The enzyme is able to carry out three interrelated reactions. First, in the oxidative half reaction, hydride transfer from the C3 of the steroid to N5 of FAD, with deprotonation of the 3C OH by Glu 475 oxidises cholesterol to form cholest-3-one. The proton is transferred to Glu 311, to allow Glu 475 to abstract a proton from the 4C and add it to the 6C to isomerise the cholest-3-one to cholest-4-en-3-one. Meanwhile, in the reductive half reaction, the reduced FAD, stabilised by contacts with Arg 477, transfers a hydride to a dioxygen molecule, which is protonated by Glu 311, forming H2O2.
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Found by:
Literature reference 

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
GLUA 311 259Sidechain
Acid/baseSubstrate
Acid/baseResidue
Accepts a proton from Glu 475 in order to allow Glu 475 to function as a base in both the oxidation and isomerisation of cholesterol. Then transfers this proton to the oxygen molecule to allow it to be reduced to H2O2.
Evidence from paper Evidence concerns Evidence type
PubMed ID 11397813 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 11397813 Current protein Conservation of residue

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
GLUA 475 423Sidechain
Acid/baseSubstrate
Acts as acid base both in the oxidative half reaction where it deprotonates the 3C OH group, and in the isomerisation step where it transfers a proton between the 4C and the 6C of the steroid ring system.
Evidence from paper Evidence concerns Evidence type
PubMed ID 11397813 Current protein Structural similarity to homologue of known mechanism
PubMed ID 11397813 Current protein Conservation of residue
PubMed ID 11397813 Current protein Residue is positioned appropriately (ligand position known)

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
ARGA 477 425Sidechain
ElectrostaticCofactor
Stabilises the negative charge that develops on the flavin ring system during its reduction.
Evidence from paper Evidence concerns Evidence type
PubMed ID 11397813 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 11397813 Current protein Conservation of residue

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
FADA 700 0
Substrate
Acts as electrophile to accept hydride transfer from the substrate thus catalysing its oxidation. Then acts as nucleophile to transfer hydride ion to oxygen, reducing it to water in the process. Thus acts as an electron donor/acceptor.
Evidence from paper Evidence concerns Evidence type
PubMed ID 11397813 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 11397813 Current protein Ligand is essential for catalysis
References:
1
Oxygen access to the active site of cholesterol oxidase through a narrow channel is gated by an Arg-Glu pair.
R. Coulombe and K. Q. Yue and S. Ghisla and A. Vrielink
J Biol Chem 276, (32) 30435-41, (2001).
11397813
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