Screening of two complementary collections of Saccharomyces cerevisiae to identify enzymes involved in stereo-selective reductions of specific carbonyl compounds: an alternative to protein purification

Two collections of Saccharomyces cerevisiae strains, having open reading frames (ORFs) either overexpressed or deleted, were screened to identify cytosolic NADPH-dependent reductases involved in stereo-selective reductions of specific carbonyl compounds. As model compounds diacetyl (diketone) and ethyl acetoacetate (3-oxo ester) were used. The reductases encoded by YBR149w, YDR368w, YMR226c and YOR120w were found to reduce diacetyl and YOL151w, YHR104w, YGL157w, YOR120w and YDR368w reduced ethyl acetoacetate. We cloned YBR149w, YDR368w and YMR226c using a vector with the strong constitutive GPD promotor and investigated the encoded reductases with respect to reduction of diacetyl. YBR149w, YDR368w and YMR226c were shown to encode (S)-specific diacetyl reductases capable of further reducing racemic acetoin to butanediol. Furthermore, we demonstrated that the purified (S)-diacetyl reductase (EC 1.2.1.56) most likely is the d-arabinose dehydrogenase encoded by YBR149w (Ara1p).