Gene Cloning and Characterization of Two NADH-Dependent 3-Quinuclidinone Reductases from Microbacterium luteolum JCM 9174
ABSTRACTWe used the resting-cell reaction to screen approximately 200 microorganisms for biocatalysts which reduce 3-quinuclidinone to optically pure (R)-(−)-3-quinuclidinol.Microbacterium luteolumJCM 9174 was selected as the most suitable organism. The genes encoding the protein products that reduced 3-quinuclidinone were isolated fromM. luteolumJCM 9174. ThebacCgene, which consists of 768 nucleotides corresponding to 255 amino acid residues and is a constituent of the bacilysin synthetic gene cluster, was amplified by PCR based on homology to known genes. Theqnrgene consisted of 759 nucleotides corresponding to 252 amino acid residues. Both enzymes belong to the short-chain alcohol dehydrogenase/reductase (SDR) family. The genes were expressed inEscherichia colias proteins which were His tagged at the N terminus, and the recombinant enzymes were purified and characterized. Both enzymes showed narrow substrate specificity and high stereoselectivity for the reduction of 3-quinuclidinone to (R)-(−)-3-quinuclidinol.