Engineering enzymes for improved catalytic efficiency: a computational study of site mutagenesis in epothilone-B hydroxylase

Epothilone F, 21-hydroxyl-epothilone B, is an intermediate in the synthesis of BMS-310705, an antitumor compound that has been evaluated in Phase I clinical trials. A bioconversion process utilizing the Gram-positive bacterium Amycolatopsis orientalis was used to prepare epothilone F from epothilone B. In order to improve the yield of epothilone F, a mutagenesis program was performed with the goal of engineering the epothilone-B hydroxylase (EBH) enzyme to improve the yield of epothilone F through oxidative biotransformation. The mutations in EBH increased the yield of epothilone F from 21% in the recombinant expression system to higher than 80% utilizing the best EBH mutants. The studies described here show how a homology model of EBH was used to obtain an understanding of the possible mechanism that led to improved yield of epothilone F in the mutated enzymes. A novel aspect of this study is that it provides some insight into how mutations distant from the binding site can affect enzyme activity.