Searching for the physiological function of 17β-hydroxysteroid dehydrogenase from the fungus Cochliobulus lunatus:: studies of substrate specificity and expression analysis

17 beta -hydroxysteroid dehydrogenase from the filamentous fungus Cochliobolus lunatus (17 beta -HSDcl) has recently been characterized. Since its function is still unclear, we performed substrate specificity studies to obtain some indications about its physiological function. Different steroids were studied as putative substrates of recombinant 17 beta -HSDcl, androgens and estrogens, brassinosteroids, and the fungal steroid herbarulid. Among these androgens and estrogens were most efficiently converted. The Following substrates in decreasing order were best reduced: 4-estrene-3,17-dione, 5 alpha -androstane-3,17-dione, 4-androstene-3,17-dione and estrone. Two typical inhibitors were tested: carbenoxolone - a representative inhibitor of the SDR family and quercetin - a diagnostic inhibitor of carbonyl reductases. Among these two quercetin was more efficient. Expression studies revealed that 17 beta -HSDcl is mainly expressed in the stationary phase of growth indicating its possible involvement in secondary metabolism. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.