Steroid modification by filamentous fungus Drechslera sp.: Focus on 7-hydroxylase and 17β-hydroxysteroid dehydrogenase activities

Fungal strain Drechslera sp. Ph F-34 was shown to modify 3-oxo- and 3-hydroxy steroids of androstane series to form the corresponding allylic 7-alcohols and 17β-reduced derivatives thus evidencing the presence of 7α-, 7β-hydroxylase and 17β-hydroxysteroid dehydrogenase (17β-HSD) activities. The growing mycelium predominantly hydroxylated androsta-1,4-diene-3,17-dione (ADD) at the 7β-position, while much lower 7α-hydroxylation was observed. Along with 7β-hydroxy-ADD and its corresponding 7α-isomer, their respective 17β-alcohols were produced. In this study, transformation of ADD, androst-4-en-17β-ol-3-one (testosterone, TS) and 3β-hydroxyandrost-5-en-17-one (dehydroepiandrosterone, DHEA) by resting mycelium of Drechslera sp. have been estimated in different conditions with regard to the inducibility and functionality of the 17β-HSD and 7-hydroxylase enzyme systems. Steroids of androstane, pregnane and cholane series were evaluated as inducers. The inhibitory analysis was provided using cycloheximide (CHX). Steroids were assayed using TLC and HPLC methods, and the structures were confirmed by mass-spectrometry, 1H and 13C NMR spectroscopy data. 17β-HSD of the mycelium constitutively reduced 17-carbonyl group of ADD and DHEA to form the corresponding 17β-alcohols, namely, androsta-1,4-diene-17β-ol-3-one (1-dehydro-TS), and androst-5-ene-3β,17β-diol. Production of the 7α- and 7β-hydroxylated derivatives depended on the induction conditions. The inducer effect relied on the steroid structure and decreased in the order: DHEA > pregnenolone > lithocholic acid. β-Sitosterol did not induce hydroxylase activity in Drechslera sp. CHX fully inhibited the synthesis of 7-hydroxylase in Drechslera mycelium thus providing selective 17-keto reduction. Results contribute to the diversity of steroid modifying enzymes in fungi and can be used at the development of novel biocatalysts for production of valuable steroid 7(α/β)- and 17β-alcohols.