Crystallization and preliminary X-ray diffraction analysis of a recombinant bacterial heme oxygenase (Hmu O) from Corynebacterium diphtheriae

Hmu O is a 24-kDa soluble bacterial heme degradation enzyme found in the pa thogen Corynebacterium diphtheriae, the causative agent of diphtheria. Simi lar to the mammalian heme oxygenase, it binds hemin stoichiometrically and catalyzes the oxygen-dependent conversion of hemin to biliverdin, carbon mo noxide, and free iron. Iron is an essential nutrient for bacteria and espec ially important for pathogenesis. Here we report the first crystallization and preliminary crystallographic study of the heme-Hmu O complex formed fro m hemin and a recombinant Hmu O, which was expressed in Escherichia coli fr om a synthetic gene based on the putative hmu O gene sequence. Crystals of the heme Hmu O complex were obtained by the sitting drop vapor diffusion me thod using a precipitant solution containing 18% (w/v) PEG 8000 and 0.2 M c alcium acetate in 0.1 M sodium cacodylate (pH 6.5). Using synchrotron radia tion, the heme-Hmu O crystal diffracted to 2.8 Angstrom resolution. It belo ngs to the monoclinic space group C2, with unit cell parameters a = 123.18 Angstrom, b = 44.51 Angstrom, c = 92.10 Angstrom, and beta = 123.3 degrees. Assuming one molecule of the heme-Hmu O complex per asymmetric unit, the c alculated value of V-m is 2.89 Angstrom(3)/Da. (C) 1999 Academic Press.