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Identification of a plausible biosynthetic enzyme for the IM-2-type autoregulator in Streptomyces antibioticus
Authors:Noriyasu Shikura  Takuya Nihira  Yasuhiro Yamada
Institution:Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
Abstract:Virginiae butanolides (VBs) and IM-2 are members of Streptomyces hormones called ‘butyrolactone autoregulators’ which regulate the antibiotic production in Streptomyces species at nanomolar concentrations. Cell-free extract of a VB-A overproducer, Streptomyces antibioticus NF-18, is capable of catalyzing the final step of the autoregulator biosynthesis, namely, the NADPH-dependent reduction of 6-dehydroVB-A. However, physico-chemical analyses of the purified enzymatic products revealed that, in addition to the VB-type isomer (2R,3R,6S)-enantiomer], IM-2-type isomers (2R,3R,6R)- and (2S,3S,6S)-enantiomers] were also produced from (±)-6-dehydroVB-A, suggesting the existence of several 6-dehydroVB-A reductases with respective stereoselectivities. The reductase activity of the crude extracts was separated into two activity peaks, peak I (major) and peak II (minor), by DEAE-5PW HPLC. Chiral HPLC analyses demonstrated that peak I enzyme and peak II enzyme catalyzed the production of (2R,3R,6S), (2R,3R,6R) and (2S,3S,6S) isomers at ratios of 46:1:3.2 and 4.9:1:1.5, respectively, indicating clearly that S. antibioticus NF-18 possesses at least two 6-dehydroVB-A reductases: one much favored toward VB-A biosynthesis, the other with relaxed stereoselectivity capable of synthesizing both VB-type and IM-2-type autoregulators.
Keywords:Butyrolactone autoregulator  Biosynthetic enzyme  IM-2  6-Dehydrovirginiae butanolide A  Corresponding author  Fax: +81-6-6879-7432
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