Crystallization and preliminary X-ray crystallographic studies on the class II cholesterol oxidase from Burkholderia cepacia containing bound flavin

Burkholderia cepacia cholesterol oxidase (ChoS) is a 58.7 kDa molecular-weight flavoenzyme which has been categorized as a 3β-hydroxysteroid oxidase converting the 3β-hydroxyl group of a range of hydroxysteroids to the corresponding ketone. Analysis of enzymes with this activity has shown that two classes of cholesterol oxidase can be defined. Enzymes belonging to class I contain non-covalently bound FAD, whereas the class II enzymes contain FAD covalently bound to an active-site histidine. Despite catalysing the same chemical reaction, the class I and class II enzymes show no sequence similarity and have a different molecular architecture. Crystals of a recombinant class II enzyme from B. cepacia have been grown by the hanging-drop vapour-diffusion method using polyethylene glycol as a precipitating agent. The crystals belong to space group P3₁21, with unit-cell parameters a = b = 119.6, c = 101.1 Å, and have one subunit in the asymmetric unit. These crystals diffract to at least 2.0 Å resolution at the Daresbury SRS and are suitable for a full structure determination. Ultimately, analysis of the structure of B. cepacia ChoS may allow the characteristics and structural features which contribute to its suitability as a diagnostic reagent for the detection of cholesterol and unresolved mechanistic features of the class II enzymes to be understood.