Crystallization and preliminary X-ray diffraction analysis of a dihaem cytochromecperoxidase fromParacoccus denitrificans

Cytochrome c peroxidase was isolated from Paracoccus denitrificans and purified to homogeneity in three steps prior to crystallization. Two different diffraction-quality crystal forms were obtained by the hanging-drop vapour-diffusion method using a number of screening conditions. The best (needle-shaped) crystal form is suitable for structural studies and was grown from solutions containing 20% PEG 8000, 0.1 M Tris pH 8.5 and 0.2 M MgCl(2). Crystals grew to a maximum length of approximately 0.7 mm and belong to the primitive monoclinic space group P2(1), with unit-cell parameters a = 78.3, b = 51.0, c = 167.2 A, beta = 97.9 degrees. After a dehydration step and extensive optimization of the cryocooling conditions, a complete data set was collected to 2.2 A from a native crystal of the fully oxidized form of the enzyme using synchrotron radiation.