Overproduction and characterization of the erythromycin C-12 hydroxylase, EryK

Hydroxylation of C-12 is one of the final steps in the biosynthesis of erythromycin A (ErA). A point of uncertainty in the erythromycin pathway has been whether the C-12 hydroxylase operates on each of two possible substrates, erythromycin B (ErB) and erythromycin D (ErD). Stassi et al. have cloned the gene, designated eryK, which encodes the P-450 monooxygenase responsible for erythromycin C-12 hydroxylation in Saccharopolyspora erythraea [Stassi, D., Donadio, S., Staver, M. J., & Katz, L. (1993) J. Bacteriol. 175, 182-189]. We report the overproduction of EryK in Escherichia coli as insoluble inclusion bodies; the solubilization, refolding, and reconstitution of active holo-EryK; and kinetic confirmation of a 1200-1900-fold preference of the enzyme for ErD over the alternative C-12 hydroxylase substrate ErB. Our results indicate that ErB is a shunt metabolite in the erythromycin biosynthetic pathway.