Diversity in Reduction with Short-Chain Dehydrogenases: Tetrahydroxynaphthalene Reductase, Trihydroxynaphthalene Reductase, and Glucose Dehydrogenase

NAD(P)H-dependent oxidoreductases from the short-chain dehydrogenases/reductases (SDRs) family possess high functional diversity. Three SDRs, namely, tetrahydroxy- and trihydroxynaphthalene reductases (T4HNR, T3HNR) involved in the dihydroxynaphthalene-melanin biosynthesis of the phytopathogenic fungus Magnaporthe grisea, and glucose dehydrogenase (GDH) from Bacillus subtilis, were characterized regarding their substrate range and functional behavior. T4HNR and T3HNR share activities towards the stereoselective reduction of 2-tetralone derivatives and 2,3-dihydro-1,4-naphthoquinones and show distinct but different stereochemical outcome in the case of epoxy-1,4-napthoquinones as substrates. GDH shares the activity towards 2,3-dihydro-1,4-naphthoquinones, however, with low stereocontrol. Moreover, GDH reduces 2-hydroxy-2,3-dihydro-1,4-naphthoquinone into trans-4-hydroxyscytalone with a high diastereomeric excess (96%), whereas T4HNR gave the cis diastereomer (diastereomeric excess>99%). Thus, SDRs provide a much higher functional and stereochemical diversity than previously thought, already exemplified by many transformations of three members of this enzyme family.