Biology Department Seminar

Cholesterol oxidase is a bifunctional flavoenzyme that catalyzes the oxidation and isomerization of D5-6-ene-3(beta)ketosteroids. The enzyme constitutes an important virulent factor in patients suffering from tuberculosis and coccobacillus infections and thus constitutes a potential new target for antibacterial drug design. Such work would benefit from a detailed understanding of the structural events that occur along the catalytic pathway of the enzyme. Sub-Angstrom resolution structures of the enzyme from Streptomyces sp. using crystals grown at different pH reveal changes to the structure as a function of electrostatic changes. These electrostatic changes can be correlated with spectral features and kinetic data. Further structural studies of a double mutant of the enzyme in the presence of a bound ligand identify a proposed Michaelis complex. A distortion of the isoalloxazine moiety of the cofactor suggests that tuning of the FAD redox potential is caused by Michaelis complex formation during catalysis. These structural studies have expanded our understanding of the interplay between the enzyme, cofactor and substrate.