Purification, Properties, and Characterization of Recombinant Streptomyces sp. Strain C5 DoxA, a Cytochrome P-450 Catalyzing Multiple Steps in Doxorubicin Biosynthesis

DoxA is a cytochrome P-450 monooxygenase involved in the late stages of daunorubicin and doxorubicin biosynthesis that has a broad substrate specificity for anthracycline glycone substrates. Recombinant DoxA was purified to homogeneity from Streptomyces lividans transformed with a plasmid containing the Streptomyces sp. strain C5 doxA gene under the control of the strong SnpR-activated snpA promoter. The purified enzyme was a monomeric, soluble protein with an apparent M(r) of 47,000. Purified DoxA catalyzed the 13-hydroxylation of 13-deoxydaunorubicin, the 13-oxidation of 13-dihydrocarminomycin and 13-dihydrodaunorubicin, and the 14-hydroxylation of daunorubicin. The pH optimum for heme activation was pH 7.5, and the temperature optimum was 30°C. The k(cat)/K(m) values for the oxidation of anthracycline substrates by purified DoxA, incubated with appropriate electron-donating components, were as follows: for 13-deoxydaunorubicin, 22,000 M(−1) · s(−1); for 13-dihydrodaunorubicin, 14,000 M(−1) · s(−1); for 13-dihydrocarminomycin, 280 M(−1) · s(−1); and for daunorubicin, 130 M(−1) · s(−1). Our results indicate that the conversion of daunorubicin to doxorubicin by this enzyme is not a favored reaction and that the main anthracycline flux through the late steps of the daunorubicin biosynthetic pathway catalyzed by DoxA is likely directed through the 4-O-methyl series of anthracyclines.