Escherichia coli kduD encodes an oxidoreductase that converts both sugar and steroid substrates

A previously unidentified oxidoreductase from Escherichia coli catalyzes the regioselective reduction of eukaryotic steroid hormone 11-deoxycorticosterone (11-DOC) to the valuable bioactive product 4-pregnen-20,21-diol-3-one. In nature, a reduction of C-20 carbonyl of C21 steroids is catalyzed by diverse NAD(P)H-dependent oxidoreductases. Enzymes that possess 20-ketosteroid reductase activity, however, have never before been described in E. coli. Our present study aimed to identify and characterize the E. coli enzyme which possesses 20-ketosteroid reductase activity against eukaryotic steroid hormone 11-DOC. We partially purified the enzyme from E. coli DH5α using protein chromatography techniques. Mass spectrometry revealed the presence of three NADH-specific oxidoreductases in the sample. The genes encoding these oxidoreductases were cloned and overexpressed in E. coli UT5600 (DE3). Only the overexpression of 2-dehydro-3-deoxy-D-gluconate 5-dehydrogenase (KduD) encoded by kduD gene enabled the whole-cell biotransformation of 11-DOC. A 6xHis-tagged version of KduD was purified to homogeneity and found to reduce several eukaryotic steroid hormones and catalyze the conversion of novel sugar substrates. KduD from E. coli is therefore a promiscuous enzyme that has a predicted role in sugar conversion in vivo but can be used for the production of valuable bioactive 20-hydroxysteroids.