Identification of a plausible biosynthetic enzyme for the IM-2-type autoregulator in Streptomyces antibioticus.
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.
Shikura
N
N
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Nihira
T
T
Yamada
Y
Y
D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000096:biosynthesis* / Q000737:chemistry; D002474:Cell-Free System; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D010088:Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D013291:Streptococcus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*
C052544:virginiamycin butanolide A; C107543:IM 2 autoregulator; D010088:Oxidoreductases; D015107:4-Butyrolactone