Cholesterol oxidase: biochemistry and structural features

• Published in: The FEBS journal Vol. 276; no. 23; pp. 6826 - 6843
• Main Authors: Vrielink, Alice, Ghisla, Sandro
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-12-2009; Blackwell Publishing Ltd
• Subjects: Amino Acid Sequence; Animals; Binding Sites; Biochemistry; Catalysis; Catalytic Domain; Cholesterol; cholesterol oxidase; Cholesterol Oxidase - chemistry; Cholesterol Oxidase - metabolism; enzyme kinetics; enzyme mechanism; flavoenzyme; Humans; Kinetics; Models, Molecular; Molecular Sequence Data; Molecular structure; Oxidation-Reduction; oxygen channel; protein structure; Protein Structure, Tertiary; redox catalysis; Sequence Alignment; Structure-Activity Relationship; Substrate Specificity
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/j.1742-4658.2009.07377.x

Cholesterol oxidases are bifunctional flavoenzymes that catalyze the oxidation of steroid substrates which have a hydroxyl group at the 3β position of the steroid ring system. The enzyme is found, in a wide range of bacterial species, in two forms: one with the FAD cofactor bound noncovalently to the enzyme; and one with the cofactor linked covalently to the protein. Here we discuss, compare and contrast the salient biochemical properties of the two forms of the enzyme. Specifically, the structural features are discussed that affect the redox potentials of the flavin cofactor, the chemical mechanism of substrate dehydrogenation by active-center amino acid residues, the kinetic parameters of both types of enzymes and the reactivity of reduced enzymes with molecular dioxygen. The presence of a molecular tunnel that is proposed to serve in the access of dioxygen to the active site and mechanisms of its control by a 'gate' formed by amino acid residues are highlighted.