The role of Ala231 and Trp227 in the substrate specificities of fungal 17β-hydroxysteroid dehydrogenase and trihydroxynaphthalene reductase: Steroids versus smaller substrates

► Trihydroxynaphthalene reductase converts substrates with two rings, like DDBO. ► 17β-Hydroxysteroid dehydrogenase converts four-ring substrates, like steroids. ► 17β-HSDcl Ala231Trp mutant better reduces PQ and shows low conversion of steroids. ► 3HNR Trp227Ala mutant better converts steroids and PQ, and less DDBO. ► Ala231 in 17β-HSDcl and Trp227 in 3HNR affect binding of larger/smaller substrates.