A novel 17 beta-hydroxysteroid dehydrogenase in the fungus Cochliobolus lunatus: new insights into the evolution of steroid-hormone signalling

17 beta-Hydroxysteroid dehydrogenase (17 beta-HSD) from the filamentous fun gus Cochliobolus lunatus (17 beta-HSDcl) catalyses the reduction of steroid s and of several o- and p-quinones. After purification of the enzyme, its p artial amino acid sequence was determined. A PCR fragment amplified with pr imers derived from peptide sequences was generated for screening the Coch. lunatus cDNA library. Three independent full-length cDNA clones were isolat ed and sequenced, revealing an 810-bp open reading frame encoding a 270-ami no-acid protein. After expression in Escherichia coli and purification to h omogeneity, the enzyme was found to be active towards androstenedione and m enadione, and was able to form dimers of M-r 60 000. The amino acid sequenc e of the novel 17 beta-HSD demonstrated high homology with fungal carbonyl reductases, such as versicolorin reductase from Emericella nidulans (Asperg illus nidulans; VerA) and Asp. parasiticus (Ver1), polyhydroxynaphthalene r eductase from Magnaporthe grisea, the product of the Brn1 gene from Coch. h eterostrophus and a reductase from Colletotrichum lagenarium, which are all members of the short-chain dehydrogenase/reductase superfamily. 17 beta-HS Dcl is the first discovered fungal 17 beta-hydroxysteroid dehydrogenase bel onging to this family. The primary structure of this enzyme may therefore h elp to elucidate the evolutionary history of steroid dehydrogenases.