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

Tubeleviciute A, Teese MG, Jose J

Abstract

A previously unidentified oxidoreductase from Escherichiacoli 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 KduD (2‑dehydro‑3‑deoxy‑D‑gluconate5‑dehydrogenase) 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 invivo, but can be used for the production of valuable bioactive 20‑hydroxysteroids.