4U2S

Cholesterol oxidase in the reduced state complexed with isopropanol

Summary for 4U2S

• Entry DOI: 10.2210/pdb4u2s/pdb
• Descriptor: Cholesterol oxidase, SULFATE ION, DIHYDROFLAVINE-ADENINE DINUCLEOTIDE, ... (4 entities in total)
• Functional Keywords: cholesterol oxidase, flavoenzymes, redox chemistry, oxidoreductase, isomerase
• Biological source: Streptomyces sp.
• Cellular location: Secreted: P12676
• Total number of polymer chains: 1
• Total formula weight: 56970.36

Authors

Golden, E.A.,Vrielink, A. (deposition date: 2014-07-18, release date: 2014-12-10, Last modification date: 2023-12-27)

Primary citation

Golden, E.,Karton, A.,Vrielink, A.
High-resolution structures of cholesterol oxidase in the reduced state provide insights into redox stabilization.
Acta Crystallogr.,Sect.D, 70:3155-3166, 2014

PubMed Abstract: Cholesterol oxidase (CO) is a flavoenzyme that catalyzes the oxidation and isomerization of cholesterol to cholest-4-en-3-one. The reductive half reaction occurs via a hydride transfer from the substrate to the FAD cofactor. The structures of CO reduced with dithionite under aerobic conditions and in the presence of the substrate 2-propanol under both aerobic and anaerobic conditions are presented. The 1.32 Å resolution structure of the dithionite-reduced enzyme reveals a sulfite molecule covalently bound to the FAD cofactor. The isoalloxazine ring system displays a bent structure relative to that of the oxidized enzyme, and alternate conformations of a triad of aromatic residues near to the cofactor are evident. A 1.12 Å resolution anaerobically trapped reduced enzyme structure in the presence of 2-propanol does not show a similar bending of the flavin ring system, but does show alternate conformations of the aromatic triad. Additionally, a significant difference electron-density peak is observed within a covalent-bond distance of N5 of the flavin moiety, suggesting that a hydride-transfer event has occurred as a result of substrate oxidation trapping the flavin in the electron-rich reduced state. The hydride transfer generates a tetrahedral geometry about the flavin N5 atom. High-level density-functional theory calculations were performed to correlate the crystallographic findings with the energetics of this unusual arrangement of the flavin moiety. These calculations suggest that strong hydrogen-bond interactions between Gly120 and the flavin N5 centre may play an important role in these structural features.

PubMed: 25478834
DOI: 10.1107/S139900471402286X

Experimental method

X-RAY DIFFRACTION (1.12 Å)