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

17 beta -hydroxysteroid dehydrogenase from the filamentous fungus Cochliobo lus lunatus (17 beta -HSDcl) has recently been characterized. Since its fun ction is still unclear, we performed substrate specificity studies to obtai n some indications about its physiological function. Different steroids wer e studied as putative substrates of recombinant 17 beta -HSDcl, androgens a nd estrogens, brassinosteroids, and the fungal steroid herbarulid. Among th ese androgens and estrogens were most efficiently converted. The Following substrates in decreasing order were best reduced: 4-estrene-3,17-dione, 5 a lpha -androstane-3,17-dione, 4-androstene-3,17-dione and estrone. Two typic al inhibitors were tested: carbenoxolone - a representative inhibitor of th e 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 i ndicating its possible involvement in secondary metabolism. (C) 2001 Elsevi er Science Ireland Ltd. All rights reserved.