Maximum virginiamycin production by optimization of cultivation conditions in batch culture with autoregulator addition

A strategy for optimization of non-growth-associated production in batch culture employing an empirical approach was developed through the study of virginiamycin production. The strategy is formulated with two aims: attaining a high cell concentration at the beginning of the production phase without decrease in production activity; and enhancing the production activity during the production phase. As a practical example, the goal of a maximum virginiamycin (M and S) production in the batch culture of Streptomyces virginiae was set. To attain a high cell concentration in the production phase of the batch culture, that is, to extend the growth phase for as long as possible, the optimum composition and concentration of the complex medium, especially the yeast extract (YE) concentration, were first investigated. Dissolved oxygen (DO) concentration control was also a parameter considered in maintaining the production activity during the production phase. In addition, to enhance the production activity, an optimum addition strategy of an autoregulator, virginiae butanolide-C (VB-C), was investigated. Combining these measures, the optimum cultivation conditions were found to be an initial YE concentration in the complex medium of 45 g/L, the shot addition of 300 mug/L of VB-C 11.5 h after the start of the batch culture, and a DO concentration maintained above 2 mg/L. The maximum concentrations of virginiamycin M and S were about ninefold those obtained under nonoptimum cultivation conditions. Nonoptimum cultivation conditions consisted of an initial YE concentration one sixth (7.5 g/L) that of the optimum cultivation conditions, and no VB-C addition. These conditions were used as representative of the standard cultivation of virginiamycin in this study. The strategy developed here will be applicable to the production of other antibiotics, especially to the cultivation of Streptomyces species, in which a hormonelike signal material (an autoregulator) plays an important role in antibiotic production. (c) 1996 John Wiley & Sons, Inc.

Oxidative Pathway from Squalene to Geranylacetone in Arthrobacter sp. Strain Y-11

The reaction pathway from squalene to trans-geranylacetone in Arthrobacter sp. strain Y-11 was studied. The enzyme or enzymes catalyzing squalene degradation were found to be membrane bound. Stoichiometric analysis of a cell-free system revealed that the ratio of squalene to trans-geranylacetone changed from 1:2 to 1:1 as the reaction proceeded, indicating two steps in geranylacetone formation. The initial step was found to be oxygenase catalyzed, from the absolute requirement for molecular oxygen in geranylacetone formation and the incorporation of O into geranylacetone under O(2) atmosphere. By using [H]squalene as the substrate, we detected an intermediate in the pathway and identified it as 5,9,13-trimethyltetradeca-4,8,12-trienoic acid by mass spectrometry, infrared spectrometry, nuclear magnetic resonance spectrometry, and chemical synthesis. We deduced that squalene was first oxidatively cleaved to geranylacetone and the intermediate, and that the intermediate was further metabolized to geranylacetone. We also synthesized some of the presumptive metabolites, such as 4,8,12-trimethyltrideca-4,8,12-trien-2-one, and confirmed that they served as active precursors for geranylacetone formation. Based on these lines of evidence, we present here the pathway from squalene to trans-geranylacetone in Arthrobacter sp. strain Y-11.

Fabrication of size-controlled polyimide nanoparticles

Polyimide particles were fabricated through the two-steps imidization of poly(amic acid) particles prepared by using reprecipitation method. PAA and PI nanoparticles were all spherical, and the changes of particle size, its distribution, and morphology were not observed before and after the imidization. The preparation of PI nanoparticles size-controlled between ca. 20-500 nm was also achieved by changing the experimental conditions, temperature of the poor solvent, the composition of two kind of poor solvent, and PAA-NMP solution concentration.

Neuronal specificity of alpha-synuclein toxicity and effect of Parkin co-expression in primates

Recombinant adeno-associated viral (rAAV) vector-mediated overexpression of alpha-synuclein (alphaSyn) protein has been shown to cause neurodegeneration of the nigrostriatal dopaminergic pathway in rodents and primates. Using serotype-2 rAAV vectors, we recently reported the protective effect of Parkin on alphaSyn-induced nigral dopaminergic neurodegeneration in a rat model. Here we investigated the neuronal specificity of alphaSyn toxicity and the effect of Parkin co-expression in a primate model. We used another serotype (type-1) of AAV vector that was confirmed to deliver genes of interest anterogradely and retrogradely to neurons in rats. The serotype-1 rAAV (rAAV1) carrying alphaSyn cDNA (rAAV1-alphaSyn), and a cocktail of rAAV1-alphaSyn and rAAV1 carrying parkin cDNA (rAAV1-parkin) were unilaterally injected into the striatum of macaque monkeys, resulting in protein expression in striatonigral GABAergic and nigrostriatal dopaminergic neurons. Injection of rAAV1-alphaSyn alone decreased tyrosine hydroxylase immunoreactivity in the striatum compared with the contralateral side injected with a cocktail of rAAV1-alphaSyn and rAAV1-parkin. Immunostaining of striatonigral GABAergic neurons was similar on both sides. Overexpression of Parkin in GABAergic neurons was associated with less accumulation of alphaSyn protein and/or phosphorylation at Ser129 residue. Our results suggest that the toxicity of accumulated alphaSyn is not induced in non-dopaminergic neurons and that the alphaSyn-ablating effect of Parkin is exerted in virtually all neurons in primates.

A complex role for the gamma-butyrolactone SCB1 in regulating antibiotic production in Streptomyces coelicolor A3(2)

Many streptomycetes produce extracellular gamma-butyrolactones. In several cases, these have been shown to act as signals for the onset of antibiotic production. Synthesis of these molecules appears to require a member of the AfsA family of proteins (AfsA is required for A-factor synthesis of the gamma-butyrolactone A-factor and consequently for streptomycin production in Streptomyces griseus). An afsA homologue, scbA, was identified in Streptomyces coelicolor A3(2) and was found to lie adjacent to a divergently transcribed gene, scbR, which encodes a gamma-butyrolactone binding protein. Gel retardation assays and DNase I footprinting studies revealed DNA binding sites for ScbR at - 4 to - 33 nt with respect to the scbA transcriptional start site, and at - 42 to - 68 nt with respect to the scbR transcriptional start site. Addition of the gamma-butyrolactone SCB1 of S. coelicolor resulted in loss of the DNA-binding ability of ScbR. A scbA mutant produced no gamma-butyrolactones, yet overproduced two antibiotics, actinorhodin (Act) and undecylprodigiosin (Red), whereas a deletion mutant of scbR also failed to make gamma-butyrolactones and showed delayed Red production. These phenotypes differ markedly from those expected by analogy with the S. griseus A-factor system. Furthermore, transcription of scbR increased, and that of scbA was abolished, in an scbR mutant, indicating that ScbR represses its own expression while activating that of scbA. In the scbA mutant, expression of both genes was greatly reduced. Addition of SCB1 to the scbA mutant induced transcription of scbR, but did not restore scbA expression, indicating that the deficiency in scbA transcription in the scbA mutant is not solely due to the inability to produce SCB1, and that ScbA is a positive autoregulator in addition to being required for gamma-butyrolactone production. Overall, these results indicate a complex mechanism for gamma-butyrolactone-mediated regulation of antibiotic biosynthesis in S. coelicolor.

Gene replacement analysis of the butyrolactone autoregulator receptor (FarA) reveals that FarA acts as a Novel regulator in secondary metabolism of Streptomyces lavendulae FRI-5

IM-2 [(2R,3R,1'R)-2-1'-hydroxybutyl-3-hydroxymethyl gamma-butanolide] is a gamma-butyrolactone autoregulator which, in Streptomyces lavendulae FRI-5, switches off the production of D-cycloserine but switches on the production of a blue pigment and several nucleoside antibiotics. To clarify the in vivo function of an IM-2-specific receptor (FarA) in the IM-2 signaling cascade of S. lavendulae FRI-5, a farA deletion mutant was constructed by means of homologous recombination. On several solid media, no significant difference in morphology was observed between the wild-type strain and the farA mutant (strain K104), which demonstrated that the IM-2-FarA system does not participate in the morphological control of S. lavendulae FRI-5. In liquid media, the farA mutant overproduced nucleoside antibiotics and produced blue pigment earlier than did the wild-type strain, suggesting that the FarA protein acts primarily as a negative regulator on the biosynthesis of these compounds in the absence of IM-2. However, contrary to the IM-2-dependent suppression of D-cycloserine production in the wild-type strain, overproduction of D-cycloserine was observed in the farA mutant, indicating for the first time that the presence of both IM-2 and intact FarA are necessary for the suppression of D-cycloserine biosynthesis.

Identification of the varR gene as a transcriptional regulator of virginiamycin S resistance in Streptomyces virginiae

A gene designated varR (for virginiae antibiotic resistance regulator) was identified in Streptomyces virginiae 89 bp downstream of a varS gene encoding a virginiamycin S (VS)-specific transporter. The deduced varR product showed high homology to repressors of the TetR family with a conserved helix-turn-helix DNA binding motif. Purified recombinant VarR protein was present as a dimer in vitro and showed clear DNA binding activity toward the varS promoter region. This binding was abolished by the presence of VS, suggesting that VarR regulates transcription of varS in a VS-dependent manner. Northern blot analysis revealed that varR was cotranscribed with upstream varS as a 2.4-kb transcript and that VS acted as an inducer of bicistronic transcription. Deletion analysis of the varS promoter region clarified two adjacent VarR binding sites in the varS promoter.

Identification by gene deletion analysis of a regulator, VmsR, that controls virginiamycin biosynthesis in Streptomyces virginiae

Virginiae butanolide (VB)-BarA of Streptomyces virginiae is one of the newly discovered pairs of a butyrolactone autoregulator and a corresponding receptor protein of Streptomyces species and regulates the production of the antibiotic virginiamycin (VM) in S. virginiae. The gene vmsR was found to be situated 4.7 kbp upstream of the barA gene, which encodes the VB-specific receptor. The vmsR product was predicted to be a regulator of VM biosynthesis based on its high homology to some Streptomyces pathway-specific transcriptional regulators for the biosynthetic gene clusters of polyketide antibiotics, such as Streptomyces peucetius DnrI (47.5% identity, 84. 3% similarity), which controls daunorubicin biosynthesis. A vmsR deletion mutant was created by homologous recombination. Neither virginiamycin M(1) nor virginiamycin S was produced in the vmsR mutant, while amounts of VB and BarA similar to those produced in the wild-type strain were detected. Reverse transcription-PCR analyses confirmed that the vmsR deletion had no deleterious effects on the transcription of the vmsR-surrounding genes, indicating that VmsR is a positive regulator of VM biosynthesis in S. virginiae.

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.

Purification and structural determination of SCB1, a gamma-butyrolactone that elicits antibiotic production in Streptomyces coelicolor A3(2)

Early stationary phase culture supernatants of Streptomyces coelicolor A3(2) contained at least four small diffusible signaling molecules that could elicit precocious antibiotic synthesis in the producing strain. The compounds were not detected in exponentially growing cultures. One of these compounds, SCB1, was purified to homogeneity and shown to be a gamma-butyrolactone of structure (2R, 3R,1'R)-2-(1'-hydroxy-6-methylheptyl)-3-hydroxymethylbutanolide . Bioassays of chemically synthesized SCB1, and of its purified stereoisomers, suggest that SCB1 acts in a highly specific manner to elicit the production of both actinorhodin and undecylprodigiosin, the two pigmented antibiotics made by S. coelicolor.

Identification of an AfsA homologue (BarX) from Streptomyces virginiae as a pleiotropic regulator controlling autoregulator biosynthesis, virginiamycin biosynthesis and virginiamycin M1 resistance

Virginiae butanolide (VB)-BarA of Streptomyces virginiae is one of the newly discovered pairs of a gamma-butyrolactone autoregulator and the corresponding receptor protein of the Streptomyces species, and has been shown to regulate the production of antibiotic virginiamycin (VM) in S. virginiae. A divergently transcribed barX gene is situated 259 bp upstream of the barA gene, and the BarX protein has been shown to be highly homologous (39.8% identity, 74. 6% similarity) to S. griseus AfsA. Although AfsA is thought to be a biosynthetic enzyme for A-factor, another member of the family of gamma-butyrolactone autoregulators, the in vivo function of S. virginiae BarX was investigated in this study by phenotypic and transcriptional comparison between wild-type S. virginiae and a barX deletion mutant. With the same growth rate as wild-type S. virginiae on both solid and liquid media, the barX mutant showed no apparent changes in its morphological behaviour, indicating that barX does not participate in morphological control in S. virginiae. However, the barX mutant became more sensitive to virginiamycin M1 than did the wild-type strain (minimum inhibitory concentration, 50 microgram ml-1 compared with > 200 microgram ml-1) and exhibited reduced VB and VM production. The VM production was not restored by exogenous addition of VB, suggesting that BarX per se is not a biosynthetic enzyme of VBs but a pleiotropic regulatory protein controlling VB biosynthesis. DNA sequencing of a 5.6 kbp downstream region of barX revealed the presence of five open reading frames (ORFs): barZ, encoding a BarB-like regulatory protein; orf2, encoding a Streptomyces coelicolor RedD-like pathway specific regulator; varM, encoding a homologue of ATP-dependent transporters for macrolide antibiotics; orf4, encoding a homologue of beta-ketoacyl ACP/CoA reductase; and orf5, encoding a homologue of dNDP-glucose dehydratase. Reverse transcription polymerase chain reaction (RT-PCR) analyses of the downstream five genes together with those of the three upstream genes (barA, barB, encoding a regulatory protein; and varS, encoding a virginiamycin S specific transporter) revealed that, in the barX mutant, the transcriptions of barZ, orf2, varM and orf5 were completely repressed and those of barB and varS were derepressed. Because free BarA (BarA in the absence of VB) in wild-type S. virginiae represses the transcription of bicistronic barB-varS operon through binding to a specific DNA sequence (BarA-responsive element, BARE) overlapping the barB transcriptional start site, the derepression of barB-varS transcription in the barX mutant suggested that the in vivo function of BarA was impaired by the lack of BarX protein. Gel-shift assays revealed that BarA easily lost its DNA-binding activity in the absence of BarX but that the defect was restored by the presence of recombinant BarX as a fusion with maltose-binding protein (MBP-BarX), whereas MBP-BarX itself showed no DNA-binding activity, indicating that BarX is likely to be a co-repressor of BarA, enforcing the DNA-binding activity of BarA through protein-protein interactions.

Glutathione as an essential factor for chaperon-mediated activation of lactonizing lipase (LipL) from Pseudomonas sp. 109

Pseudomonas sp. 109 produces a unique lipase (LipL) which efficiently catalyzes intramolecular transesterification of omega-hydroxyesters to form macrocyclic lactones. The production of the enzymatically active LipL requires a specific molecular chaperon (LimL protein) together with a low-M(r) lipase-activation-factor (LAF) of unknown structure. From 50 g of Pseudomonas cells, 2.15 mg of LAF was purified as a sulfobenzofurazanyl derivative after methanol extraction, derivatization, and C(18) reverse-phase HPLC. One-dimensional and two-dimensional 600 MHz (1)H-NMR and fast atom bombardment mass spectrometry (FAB-MS) revealed that LAF is glutathione. Because several SH compounds (L-cysteine and mercaptoethanol) were similarly effective to native LAF in the activation of LipL, and because only LipL contains two cysteinyl residues forming an intramolecular disulfide bond, it is concluded that the reduction of and reformation of the intramolecular disulfide bond of LipL is essential to liberate free and fully active LipL.

A null mutant of the Streptomyces virginiae barA gene encoding a butyrolactone autoregulator receptor and its phenotypic and transcriptional analysis

The Streptomyces virginiae barA gene encodes a specific receptor protein for virginiae butanolide (VB), one of the gamma-butyrolactone autoregulators of Streptomyces species. By homologous recombination, a barA null strain was constructed to clarify the in vivo function of BarA protein in S. virginiae. The deltabarA mutant showed no difference in terms of growth, but lost VB production and produced virginiamycin 7 h earlier than the wild-type strain. These results indicated that, phenotypically, BarA protein acts negatively in virginiamycin biosynthesis and positively in VB biosynthesis. Furthermore, Northern (RNA) blot analysis of the DeltabarA mutant revealed that transcription of the BarA target gene (barB) was derepressed, confirming that BarA acts as a transcriptional repressor in S. virginiae.

Purification and characterization of a novel extracellular lipase catalyzing hydrolysis of oleyl benzoate from Acinetobacter nov. sp. strain KM109

A new lipase (OBase) which efficiently hydrolyzes oleyl benzoate (OB) was found in the culture supernatant of Acinetobacter nov. sp. strain KM109, a new isolate growing in a minimum medium containing OB as the sole carbon source. OBase was purified to homogeneity with 213-fold purification and 0.8% yield. The molecular weight was estimated to be 62,000 +/- 1,000 by SDS-PAGE under denatured-reduced conditions and to be 50,000 +/- 1,000 by gel-filtration HPLC under native conditions; these findings indicate that OBase is a monomeric enzyme. The optimum temperature and pH of OBase were about 45 degrees C and pH 8. Temperature and pH stabilities were at or lower than 35 degrees C and in a range of pH 6-8, respectively. Purified OBase preferentially hydrolyzed p-nitrophenyl benzoate (pNPB) over p-nitrophenyl acetate (pNPA) or p-nitrophenyl caproate (pNPC) [pNPB/pNPA = 20 and pNPB/pNPC = 5.4], indicating that OBase has a high affinity for benzoyl esters. Partial amino-acid sequences of OBase fragments obtained after lysyl endopeptidase treatment showed no similarity with known proteins.

A low-Mr lipase activation factor cooperating with lipase modulator protein LimL in Pseudomonas sp. strain 109

Pseudomonas sp. strain 109 produces a unique lipase (LipL) which efficiently catalyses intramolecular transesterification of omega-hydroxyesters to form macrocyclic lactones. In vivo production of enzymically active LipL requires lipase modulator protein (LimL), which functions as a molecular chaperone for the correct folding of LipL. However, previous work has shown that LipL forms a tight complex with LimL in vitro and the resulting LipL-LimL complex is only partially active, suggesting an additional mechanism that facilitates the dissociation of the complex to form enzymically active LipL. In the present work, a low-Mr compound (lipase activation factor, LAF) was found in Pseudomonas sp. strain 109 that when added to the LipL-LimL complex resulted in the activation of LipL. Ca2+ ions also enhanced lipase activity, but the instantaneous activation by Ca2+ was different from the gradual and time-dependent activation by LAF, indicating the novel nature of this compound. LAF passed through an ultrafiltration membrane with an Mr cut-off of 3000 and showed an apparent Mr of 330+/-30 on Superdex Peptide gel-filtration chromatography. Treatment of the LipL-LimL complex with LAF liberated free active LipL, indicating that LAF was necessary to dissociate the LipL-LimL complex.

Characterization of binding sequences for butyrolactone autoregulator receptors in streptomycetes

BarA of Streptomyces virginiae is a specific receptor protein for a member of butyrolactone autoregulators which binds to an upstream region of target genes to control transcription, leading to the production of the antibiotic virginiamycin M(1) and S. BarA-binding DNA sequences (BarA-responsive elements [BAREs]), to which BarA binds for transcriptional control, were restricted to 26 to 29-nucleotide (nt) sequences on barA and barB upstream regions by the surface plasmon resonance technique, gel shift assay, and DNase I footprint analysis. Two BAREs (BARE-1 and BARE-2) on the barB upstream region were located 57 to 29 bp (BARE-1) and 268 to 241 bp (BARE-2) upstream from the barB translational start codon. The BARE located on the barA upstream region (BARE-3) was found 101 to 76 bp upstream of the barA start codon. High-resolution S1 nuclease mapping analysis revealed that BARE-1 covered the barB transcription start site and BARE-3 covered an autoregulator-dependent transcription start site of the barA gene. Deletion and mutation analysis of BARE-2 demonstrated that at least a 19-nt sequence was required for sufficient BarA binding, and A or T residues at the edge as well as internal conserved nucleotides were indispensable. The identified binding sequences for autoregulator receptor proteins were found to be highly conserved among Streptomyces species.

In vitro analysis of the butyrolactone autoregulator receptor protein (FarA) of Streptomyces lavendulae FRI-5 reveals that FarA acts as a DNA-binding transcriptional regulator that controls its own synthesis

FarA of Streptomyces lavendulae FRI-5 is a specific receptor protein for IM-2, a butyrolactone autoregulator that controls the production of a blue pigment and the nucleoside antibiotics showdomycin and minimycin. Gel shift assays demonstrated that FarA binds to the farA upstream region and that this binding is abolished in the presence of IM-2. The FarA binding sequence was localized by DNase I footprinting to a 28-bp sequence located approximately 70 bp upstream of the farA translational start site. High-resolution S1 nuclease mapping of farA transcripts revealed a putative transcription start site, located at an A residue positioned 64 bp upstream from the farA translation start codon and 4 bp downstream from an Escherichia coli sigma(70)-like -10 recognition region. The FarA-binding sequence overlaps this -10 region and contains the farA transcription initiation site, suggesting that FarA acts as a repressor that, in the absence of IM-2, represses transcription of farA.

Increase production of lactonizing lipase (LipL) from Pseudomonas sp. strain 109 by lipids and detergents

LipL of Pseudomonas sp. strain 109 is a unique lipase capable of catalyzing macrocyclic lactone synthesis using omega-hydroxyfatty acid esters as substrates. Several fatty acid esters were tested as inducers of LipL production. The addition of either soybean oil or a non-ionic detergent (Noigen HC) resulted in a 44 to 45-fold increase in extracellular LipL, and the presence of both resulted in a further 56-fold increase. Among the triglycerides tested, triolein was the most effective, with a 50-fold increase in LipL production. A Northern blot hybridization analysis found that the lipL transcript increased in the presence of soybean oil or Noigen HC, indicating that the production of LipL is regulated at the transcriptional level.

Identification and in vivo functional analysis of a virginiamycin S resistance gene (varS) from Streptomyces virginiae

BarA of Streptomyces virginiae is a specific receptor protein for virginiae butanolide (VB), one of the gamma-butyrolactone autoregulators of the Streptomyces species, and acts as a transcriptional regulator controlling both virginiamycin production and VB biosynthesis. The downstream gene barB, the transcription of which is under the tight control of the VB-BarA system, was found to be transcribed as a polycistronic mRNA with its downstream region, and DNA sequencing revealed a 1,554-bp open reading frame (ORF) beginning at 161 bp downstream of the barB termination codon. The ORF product showed high homology (68 to 73%) to drug efflux proteins having 14 transmembrane segments and was named varS (for S. virginiae antibiotic resistance). Heterologous expression of varS with S. lividans as a host resulted in virginiamycin S-specific resistance, suggesting that varS encoded a virginiamycin S-specific transport protein. Northern blot analysis indicated that the bicistronic transcript of barB-varS appeared 1 to 2 h before the onset of virginiamycin M1 and S production, at which time VB was produced, while exogenously added virginiamycin S apparently induced the monocistronic varS transcript.

Identification and characterization of 6-dehydroVB-A reductase from Streptomyces antibioticus

Streptomyces antibioticus NF-18 is a hyperproducing strain of a Streptomyces hormone, virginiae butanolide A (VB-A), that induces virginiamycin production of S. virginiae at nanomolar concentrations. To characterize the biosynthetic pathway of VB-A, we identified and characterized for the first time the 6-dehydro VB-A reductase that is responsible for the final reduction step in the biosynthesis. Assay protocols and stabilization conditions were established. The 6-dehydro VB-A reductase was found to require NADPH, not NADH, as a coenzyme. The K(m) values of the enzyme for NADPH and (+/-)-6-dehydro VB-A were determined to be 50 +/- 2 microM and 100 +/- 5 microM, respectively. Ultracentrifugation experiments revealed that 6-dehydro VB-A reductase was present almost exclusively in the 100,000 x g supernatant fraction, indicating that the enzyme is a cytoplasmic-soluble protein. The M(r) of the native 6-dehydro VB-A reductase was estimated to be 82,000 +/- 3000 by molecular sieve HPLC. The optimal pH was found to be 6.7 +/- 0.2.

Modulator-mediated synthesis of active lipase of Pseudomonas sp. 109 by Escherichia coli cell-free coupled transcription/translation system

Catalytically active lipase was synthesized using Escherichia coli S30 extract from the signal-deleted lipL gene (lipL) in the presence of its N-terminal hydrophobic fragment-truncated modulator (rLimL) that was purified from the overexpressing E. coli cells. The specific activity of the lipase thus synthesized was 125 times higher than that of the purified one from Pseudomonas sp. 109. No lipase activity was detected in the absence of rLimL, even though the lipase protein itself was synthesized. Active lipase was also produced in vitro by coexpression of rlipL and the modulator gene (rlimL), although a much smaller amount of the lipase was formed. In the absence of rLimL, aggregates of the lipase were formed during its folding process. The addition of rLimL proportionally raised both lipase solubility and enzyme activity. An unstable but high activity peak of the lipase was found during its folding process.

Corynebacterium terpenotabidum sp. nov., a bacterium capable of degrading squalene

The taxonomic status of Arthrobacter sp. Y-11T, which was described as a squalene-degrading bacterium, was investigated by chemotaxonomic and genetic methods. The strain possesses wall chemotype IV, MK-9(H2) as the predominant menaquinone, mycolic acids, and straight-chain, saturated and monounsaturated fatty acids, with considerable amounts of tuberculostearic acid. The DNA G+C content is 67.5 mol%. 16S rRNA gene sequence analysis and quantitative DNA-DNA hybridization experiments provided strong evidence that strain Y-11T represents a new species within the genus Corynebacterium, for which the name Corynebacterium terpenotabidum sp. nov. is proposed. The type strain of C. terpenotabidum is strain Y-11T (= IFO 14764T).

Purification and characterization of tert-butyl ester-hydrolyzing lipase from Burkholderia sp. YY62

An intracellular novel lipase which can hydrolyze t-butyl octanoate (TBO) was purified to homogeneity from crude cell-free extracts of Burkholderia (formerly Pseudomonas) sp. YY62 with 9% overall yield. Seventy-four-fold purification was achieved by ammonium-sulfate precipitation, three consecutive open-column chromatographies (DEAE anion-exchange, Sepharose CL-6B gel-filtration, and the second DEAE anion-exchange columns), and two HPLCs (TSK G2000SWXL gel-filtration and phenyl 5PW hydrophobic interaction columns). Enzymes hydrolyzing p-nitrophenyl acetate were separated into two peaks (peak I and II) on the hydrophobic HPLC, and only peak II was found to have TBO-hydrolyzing activity. The peak preparation showed a single band of 40 kDa on SDS-PAGE and a molecular mass of 39 kDa on gel-filtration under non-denatured conditions, indicating the monomeric nature of the TBO-hydrolyzing lipase. The lipase showed maximum activity at pH 7.0 and 28 degrees C. The N-terminal 15 amino acid residues were determined as Met-Asp-Phe-Tyr-Asp-Ala-Asn-Glu-Thr-Arg-His-Pro-Glu-Gln-Arg, which showed no homology to known proteins, suggesting that the purified enzyme may belong to a novel class of hydrolase.

Purification and characterization of virginiamycin M1 reductase from Streptomyces virginiae

Virginiamycin M1 (VM1), produced by Streptomyces virginiae, is a polyunsaturated macrocyclic lactone antibiotic belonging to the virginiamycin A group. S. virginiae possesses an activity which stereospecifically reduces a 16-carbonyl group of VM1, resulting in antibiotically inactive 16R-dihydroVM1. The corresponding VM1 reductase was purified to homogeneity from crude extracts of S. virginiae in five steps, with 5,650-fold purification and 23% overall yield. The N-terminal amino acid sequence was determined to be MAIKLVIA. The purified enzyme showed an apparent Mr of 73,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an Mr of 280,000 by native molecular sieve high-performance liquid chromatography, indicating the tetrameric nature of the native enzyme. NADPH served as a coenzyme for the reduction, with a Km value of 0.13 mM, but NADH did not support the reaction, even at a concentration of 5 mM, indicating the NADPH-specific nature of the enzyme. The Km for VM1 was determined to be 1.5 mM in the presence of 2 mM NADPH. In the reverse reaction, only 16R-dihydroVM1, not the 16S-epimer, served as a substrate, with a less than 0.1% overall reaction rate compared to that of the forward reaction, confirming that the VM1 reductase participates solely in VM1 inactivation in vivo.

Gene replacement analysis of the Streptomyces virginiae barA gene encoding the butyrolactone autoregulator receptor reveals that BarA acts as a repressor in virginiamycin biosynthesis

Virginiae butanolides (VBs), which are among the butyrolactone autoregulators of Streptomyces species, act as a primary signal in Streptomyces virginiae to trigger virginiamycin biosynthesis and possess a specific binding protein, BarA. To clarify the in vivo function of BarA in the VB-mediated signal pathway that leads to virginiamycin biosynthesis, two barA mutant strains (strains NH1 and NH2) were created by homologous recombination. In strain NH1, an internal 99-bp EcoT14I fragment of barA was deleted, resulting in an in-frame deletion of 33 amino acid residues, including the second helix of the probable helix-turn-helix DNA-binding motif. With the same growth rate as wild-type S. virginiae on both solid and liquid media, strain NH1 showed no apparent changes in its morphological behavior, indicating that the VB-BarA pathway does not participate in morphological control in S. virginiae. In contrast, virginiamycin production started 6 h earlier in strain NH1 than in the wild-type strain, demonstrating for the first time that BarA is actively engaged in the control of virginiamycin production and implying that BarA acts as a repressor in virginiamycin biosynthesis. In strain NH2, an internal EcoNI-SmaI fragment of barA was replaced with a divergently oriented neomycin resistance gene cassette, resulting in the C-terminally truncated BarA retaining the intact helix-turn-helix motif. In strain NH2 and in a plasmid-integrated strain containing both intact and mutated barA genes, virginiamycin production was abolished irrespective of the presence of VB, suggesting that the mutated BarA retaining the intact DNA-binding motif was dominant over the wild-type BarA. These results further support the hypothesis that BarA works as a repressor in virginiamycin production and suggests that the helix-turn-helix motif is essential to its function. In strain NH1, VB production was also abolished, thus indicating that BarA is a pleiotropic regulatory protein controlling not only virginiamycin production but also autoregulator biosynthesis.

Butyrolactone autoregulator receptor protein (BarA) as a transcriptional regulator in Streptomyces virginiae

BarA of Streptomyces virginiae is a specific receptor protein for virginiae butanolides (VBs), a member of the butyrolactone autoregulators of Streptomyces species. Sequencing around the barA gene revealed two novel open reading frames: one upstream, barX, encoding a homolog of AfsA of Streptomyces griseus and another downstream, barB. Northern (RNA) blot analysis for S. virginiae demonstrated that the addition of VB during cultivation switched on the expression of barB. An in vivo expression system in Streptomyces lividans with the use of the xylE reporter gene indicated that BarA in conjunction with VB controlled the barB promoter. Furthermore, the DNA binding ability of BarA was demonstrated in vitro for the first time by means of surface plasmon resonance and a gel-shift assay. Complex formation with VB in vitro resulted in the dissociation of BarA from DNA, thus suggesting that the VB receptor, BarA, is a transcriptional regulator and that the VB signal is transduced to the next step in the signal transduction pathway by modification of the DNA binding ability of BarA.

Cloning and characterization of the gene (farA) encoding the receptor for an extracellular regulatory factor (IM-2) from Streptomyces sp. strain FRI-5

IM-2 is a butyrolactone autoregulator that controls production of blue pigment and nucleoside antibiotics in Streptomyces sp. strain FRI-5. An IM-2-specific receptor gene, farA, was cloned from strain FRI-5, and nucleotide sequencing revealed that the farA gene consists of 666 bp encoding a 221-amino-acid protein of 24.3 kDa with an NH2-terminal amino acid sequence identical to that of purified native receptor. Another gene, farX, encoding a homolog of AfsA of Streptomyces griseus, was present upstream of farA. The monocistronic nature of the farA transcript was shown by Northern blot hybridization, and the transcript level increased upon addition of IM-2. Recombinant FarA expressed in and purified from E. coli showed clear ligand specificity toward IM-2, with a dissociation constant (Kd) for [3H]IM-2-C5 of 18.2 nM. FarA showed high overall homology to BarA (virginiae butanolide receptor from S. virginiae) and ArpA (A-factor receptor from S. griseus). Sequence alignment of the three receptor proteins revealed that the NH2-terminal region containing a helix-turn-helix DNA binding motif was highly conserved. The DNA binding motif is common in procaryotic repressors of the TetR family, suggesting that all the Streptomyces autoregulator receptors may act as transcriptional repressors.

Gene organization in the ada-rplL region of Streptomyces virginiae

The gene organization of a 7.4-kb region of the Streptomyces virginiae (Sv) chromosome was determined. The predicted open reading frames (ORFs) and their predicted products, in sequence order, were (i) ada, encoding adenosine deaminase [EC 3.5.4.4], (ii) aat, encoding a protein homologous to aspartate aminotransferase [EC 2.6.1.1], (iii) secE, encoding a protein involved in protein secretion, (iv) vbrA, encoding a NusG-like protein involved in antitermination of transcription as described by Okamoto et al. [J. Biol. Chem. 267 (1992) 1093-1098], and (v) rplKAJL, encoding the large subunits of the ribosomal proteins L11, L1, L10 and L12. Six of the ORFs (secE-rplL) were oriented in the same direction, but the other two (ada and aat) had the opposite orientation. The gene organization of the secE-rplL region in Sv was identical to that in Escherichia coli.

Stereospecific reduction of virginiamycin M1 as the virginiamycin resistance pathway in Streptomyces virginiae

In a cell extract of Streptomyces virginiae, virginiamycin M1 was inactivated in the presence of NADPH, while virginiamycin S remained intact. The inactivated product of virginiamycin M1 was isolated, and structure analysis revealed that the inactivation involves reduction of a C-16 carbonyl group leading to the formation of 16-dihydrovirginiamycin M1. Acetonide and benzylidene acetal derivatives were synthesized from the two hydroxyl groups on C-14 and C-16, and the C-16 stereochemistry was determined by 13C nuclear magnetic resonance spectroscopy. Two methyl groups of the acetonide derivative gave 13C signals of 20.1 and 30.1 ppm, indicating that the relative stereochemistry of the C-14 and C-16 hydroxy groups is syn. Furthermore, irradiation of the benzylidene methine proton gave clear nuclear Overhauser effect enhancement of the C-14 or C-16 methine protons, indicating that H-14 and H-16 were in an axial configuration. From the (14S) absolute configuration of natural virginiamycin M1 and the syn relative configuration for the C-14 and C-16 hydroxyl groups of the inactivated product, the C-16 absolute configuration of the inactivated product was thus identified as R.

Cloning and characterization of the A-factor receptor gene from Streptomyces griseus

A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) and its specific receptor protein control streptomycin production, streptomycin resistance, and aerial mycelium formation in Streptomyces griseus. The A-factor receptor protein (ArpA) was purified from a cell lysate of S. griseus IFO 13350. The NH2-terminal amino acid sequences of ArpA and lysyl endopeptidase-generated fragments were determined for the purpose of preparing oligonucleotide primers for cloning arpA by the PCR method. The arpA gene cloned in this way directed the synthesis of a protein having A-factor-specific binding activity when expressed in Escherichia coli under the control of the T7 promoter. The arpA gene was thus concluded to encode a 276-amino-acid protein with a calculated molecular mass of 29.1 kDa, as determined by nucleotide sequencing. The A-factor-binding activity was observed with a homodimer of ArpA. The NH2-terminal portion of ArpA contained an alpha-helix-turn-alpha-helix DNA-binding motif that showed great similarity to those of many DNA-binding proteins, which suggests that it exerts its regulatory function for the various phenotypes by directly binding to a certain key gene(s). Although a mutant strain deficient in both the ArpA protein and A-factor production overproduces streptomycin and forms aerial mycelium and spores earlier than the wild-type strain because of repressor-like behavior of ArpA, introduction of arpA into this mutant abolished simultaneously its streptomycin production and aerial mycelium formation. All of these data are consistent with the idea that ArpA acts as a repressor-type regulator for secondary metabolite formation and morphogenesis during the early growth phase and A-factor at a certain critical intracellular concentration releases the derepression, thus leading to the onset of secondary metabolism and aerial mycelium formation. The presence of ArpA-like proteins among Streptomyces spp., as revealed by PCR, together with the presence of A-factor-like compounds, suggests that a hormonal control similar to the A-factor system exists in many species of this genus.

Virginiae butanolide binding protein from Streptomyces virginiae. Evidence that VbrA is not the virginiae butanolide binding protein and reidentification of the true binding protein

Virginiae butanolides (VBs) A-E are butyrolactone autoregulators that control virginiamycin production in Streptomyces virginiae. We have previously reported the purification and molecular cloning of VbrA, a putative VB binding protein (Okamoto, S., Nihira, T., Kataoka, H., Suzuki, A., and Yamada, Y. (1992) J. Biol. Chem. 267, 1093-1098). However, VbrA protein overexpressed in Escherichia coli did not show any detectable VB binding activity nor did the immunoprecipitation of native VbrA from a cell-free extract of S. virginiae cause any decrease in such activity, indicating that VbrA is not the true VB binding protein. This finding prompted us to seek the true VB binding protein by repurification. After successive purification by anion exchange, gel filtration, heparin, and hydrophobic interaction chromatography, a 26-kDa protein (p26k) was identified as the true VB binding protein. Partial amino acid sequences of p26k were determined, and the gene (barA) that encodes this protein was isolated and cloned using degenerate oligonucleotide probes. When the barA gene was expressed in Streptomyces lividans and E. coli, strong VB binding activity appeared, demonstrating unambiguously that the S. virginiae p26k protein is the true VB binding protein.

Cloning, nucleotide sequence, and transcriptional analysis of the nusG gene of Streptomyces coelicolor A3(2), which encodes a putative transcriptional antiterminator

A 3 kb genomic fragment containing the nusG gene of Streptomyces coelicolor A3(2) was identified, cloned and sequenced. Sequence analysis revealed 3 complete and 2 truncated open reading frames (ORFs): truncated ORFU (similar to a Bacillus gene encoding a thermostable aspartate aminotransferase)-secE (94 amino acids; 79.0% similarity to Escherichia coli SecE)-nusG (300 amino acids; 73.3% similarity to E. coli NusG)-rplK (144 amino acids; 88.5% similarity to E. coli ribosomal subunit L11)-truncated rplA (similar to E. coli ribosomal subunit L1). The gene organization secE-nusG-rplKA exactly matches that in E. coli. Transcriptional analyses by the primer extension method revealed one transcriptional start site each for secE and nusG, and two sites for rplK. The presence of promoters was also confirmed with the aid of a promoter-probe vector.

Lipase modulator protein (LimL) of Pseudomonas sp. strain 109

Plasmids containing a Pseudomonas sp. strain 109 extracellular lipase gene (lipL) lacking NH2-terminal sequence and a lipase modulator gene (limL) lacking the NH2-terminal hydrophobic region were constructed and expressed independently in Escherichia coli by using the T7 promoter expression vector system. Recombinant LipL (rLipL) was produced as inclusion bodies, whereas recombinant LimL (rLimL) was present as a soluble protein. During in vitro renaturation of the purified rLipL inclusion bodies after they had been dissolved in 8 M urea, addition of rLimL was essential to solubilize and modulate rLipL. The solubility and activity of rLipL were influenced by the rLimL/rLipL molar ratio; the highest level of solubility was obtained at an rLimL/rLipL ratio of 4:5, whereas the highest activity level was obtained at an rLimL/rLipL ratio of 4:1. After renaturation, rLipL and rLimL were coprecipitated with anti-rLipL antibody, indicating the formation of an rLipL-rLimL complex. Activity of the native lipase purified from Pseudomonas sp. strain 109 was also inhibited by rLimL. By Western blotting (immunoblotting) with anti-rLimL antibody, native LimL was detected in Pseudomonas cells solubilized by sarcosyl treatment. LimL was purified from Pseudomonas sp. strain 109, and the NH2-terminal amino acid sequence was determined to be NH2-Leu-Glu-Pro-Ser-Pro-Ala-Pro-. We propose that to prevent membrane degradation, LimL weakens lipase activity inside the cell, especially in the periplasm, in addition to modulating lipase folding.

Purification and characterization of the IM-2-binding protein from Streptomyces sp. strain FRI-5

IM-2 [(2R,3R,1'R)-2-(1'-hydroxybutyl)-3-(hydroxymethyl)butanolide] of Streptomyces sp. strain FRI-5 is one of the butyrolactone autoregulators of Streptomyces species and triggers production of blue pigment as well as the nucleoside antibiotics showdomycin and minimycin. A tritium-labeled IM-2 analogue, 2,3-trans-2(1'-beta-hydroxy-[4',5'-3H]pentyl)-3-(hydroxymethyl)butano lide ([3H]IM-2-C5; 40 Ci/mmol), was synthesized for a competitive binding assay, and an IM-2-specific binding protein was found to be present in the crude cell extract of Streptomyces sp. strain FRI-5. During cultivation for 24 h, the specific IM-2-binding activity increased rapidly, reached a plateau at 10 to 14 h, and declined sharply thereafter, showing only 6% activity after 24 h of cultivation. A Scatchard plot of the binding data demonstrated that the dissociation constant (Kd) for [3H]IM-2-C5 was 1.3 nM, while the Kd for a 3H-labeled virginiae butanolide (VB) analogue, 2-(1'-alpha-hydroxy-[6',7'-3H]heptyl)-3-(hydroxymethyl)butanolide ([3H]VB-C7), another butyrolactone autoregulator possessing the opposite configuration at C-1' was 35 nM. Furthermore, at a 15-fold molar excess, the effectiveness of several autoregulators as nonlabeled competitive ligands against [3H]IM-2-C5 was IM-2 type > VB-C type >> A-factor type, indicating that the binding protein in Streptomyces sp. strain FRI-5 is highly specific toward IM-2. Ultracentrifugation showed that the IM-2-binding protein is present almost exclusively in the 100,000 x g supernatant fraction, indicating that the binding protein is a cytoplasmic soluble protein. The binding protein was purified by ammonium sulfate precipitation, DEAE-Sephacel chromatography, Sephacryl S-100 HR gel filtration, DEAE-5PW high-performance liquid chromatography (HPLC), and phenyl-5PW HPLC. The apparent Mr of the native IM-2-binding protein as determined by molecular sieve HPLC was about 60,000 in the presence of 0.5, 0.3, or 0.1 M KCl, while by sodium dodecyl sulfate-polyacrylamide gel electrophoresis it was about 27,000, suggesting that the native binding protein is present in the form of a dimer.

Distribution in the genus Streptomyces of a homolog to nusG, a gene encoding a transcriptional antiterminator

The presence of the vbrA gene encoding the transcriptional antiterminator NusG equivalent protein of Streptomyces virginiae was tested for in 73 Streptomyces species by Southern hybridization. Fifty-five strains (75%) including S. griseus, S. lividans TK-21 and S. coelicolor A3(2) showed clear hybridization signals, indicating wide distribution of vbrA or vbrA homologs in Streptomyces species. With hybridization patterns against 3 different probes, i.e., probes covering vbrA alone, the downstream gene rplK alone, and both vbrA-rplK, the 55 strains were classified into 4 groups. In the groups I, II and III (total 50 strains) vbrA was found to be adjacent to rplK, indicating that the gene arrangement vbrA-rplK is common in Streptomyces and that these genes may constitute a part of gene cluster encoding several components of the transcription and translation apparatus, as in Escherichia coli.

Purification and molecular cloning of a butyrolactone autoregulator receptor from Streptomyces virginiae

In streptomyces, low molecular weight compounds termed "autoregulators" have been isolated as primary signal molecules for triggering secondary metabolism and/or cytodifferentiation. Streptomyces virginiae produces a set of autoregulators termed virginiae butanolide A-E which trigger virginiamycin production, and possesses a high-affinity virginiae butanolide receptor (Kim, H.S., Nihira, T., Tada, H., Yanagimoto, M., and Yamada, Y. (1989) J. Antibiot. (Tokyo) 42, 769-778). The virginiae butanolide receptor has now been purified to apparent homogeneity with 14,000-fold purification and an 8.6% activity yield. The purified receptor showed a Mr of 36,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and a maximum ligand binding of 33.0 nmol/mg protein, indicating a 1:1 binding stoichiometry (1.18 mol of virginiae butanolide/36 kDa of protein) between virginiae butanolides and the receptor. Due to a blockage at the amino terminus, fragment peptides were generated by lysyl endopeptidase and five partial amino acid sequences were determined. The gene (vbrA) encoding the virginiae butanolide receptor was identified on a 5.0-kbp BamHI fragment by hybridization to synthetic oligonucleotide probes, cloned, and sequenced. Nucleotide-sequence analysis predicted a 319-amino acid open reading frame (vbrA) in which all the partial amino acid sequences of the receptor appeared, and 166 bp downstream from it another open reading frame for a 144-amino acid protein which was designated as a ribosomal protein L11 from its high homology (62-64%) to the amino acid sequences of ribosomal protein L11 of several origins, and thus denoted as rplK. The C-terminal half of VbrA showed 36% overall homology to the amino acid sequence of an essential protein (NusG) of Escherichia coli. Furthermore, the gene assembly of vbrA-rplk of S. virginiae closely resembled that of nusG-rplK of E. coli, suggesting that vbrA may constitute a part of an essential gene cluster encoding components of transcriptional and translational apparatuses.

Purification, characterization, and molecular cloning of lactonizing lipase from Pseudomonas species

An extracellular lipase catalyzing the synthesis of macrocyclic lactones in anhydrous organic solvents was purified to homogeneity from Pseudomonas nov. sp. 109, and characterized. The lipase showed a pI of 5.3 on isoelectric focusing and a Mr of 29,000 +/- 1,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. With respect to substrate specificity, optimum chain length for acyl moiety varied depending on the type of reaction catalyzed: C18 in monomer lactone formation, C11 or shorter in dimer lactone formation, and C8 in ester hydrolysis. The amino-terminal 19 amino acid residues of the purified lipase were determined as Ser-Thr-Tyr-Thr-Gln-Thr-Lys-Tyr-Pro-Ile-Val-Leu-Ala-His-Gly-Met-Leu-Gly- Phe, and the gene encoding the lipase was identified by hybridization to a synthetic 20-nucleotide probe, cloned, and sequenced. Nucleotide sequence analysis predicted a 311-amino acid open reading frame, a putative ribosome-binding site, and a 26-amino acid sequence at the amino terminus of the sequence that is not found in the mature protein. This 26-amino acid sequence has many of the characteristics common to known signal peptides. The lipase gene encoded a sequence of Val-Asn-Leu-Ile-Gly-His-Ser-His-Gly-Gly which is very well conserved among lipases, and showed 38-40% overall homology to the amino acid sequences of lipases from Pseudomonas fragie and Pseudomonas cepacia, but showed little homology to those of other lipases, suggesting that some structural features are required for catalyzing macrocyclic lactone synthesis in organic solvents and are restricted to lipases of the Pseudomonas origin.

Purification and characterization of virginiae butanolide C-binding protein, a possible pleiotropic signal-transducer in Streptomyces virginiae

Virginiae butanolide C (VB-C) is an autoregulator which triggers virginiamycin production in Streptomyces virginiae. A new binding assay with tritium-labeled VB-C analogue (2,3-cis-2-(1'-hydroxy-[6',7'-3H]heptyl)-3-(hydroxymethyl)butanolide+ ++ ) was developed and a specific VB-C binding protein was purified to homogeneity from crude extracts of S. virginiae by ammonium sulfate fractionation, DEAE-Sephacel and Sephadex G-100 column chromatographies, hydrophobic HPLC on phenyl 5PW and native polyacrylamide gel electrophoresis. The VB-C binding protein showed an apparent Mr of 35,800 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and Mr of 26,000 approximately 44,000 on native molecular sieve HPLC, indicating the monomeric nature of the binding protein. The binding protein efficiently bound to a VB affinity column and eluted specifically by VB-C, which confirmed the specific nature of the binding protein. The binding activity decreased by 40% in the presence of genomic DNA from S. virginiae, indicating interaction between the VB-C binding protein and the DNA.

Identification of binding protein of virginiae butanolide C, an autoregulator in virginiamycin production, from Streptomyces virginiae

In Streptomyces virginiae, production of virginiamycin is triggered by signal molecules named virginiae butanolide A, B or C (VB-A, B or C: Yamada, Y. et al. J. Antibiotics 40: 496-504, 1987). We have found a specific VB-C binding protein from S. virginiae, and characterized it by using a tritium-labeled VB-C analogue as a ligand. By equilibrium dialysis in the absence and presence of radio-inert VB-C, a crude extract from 1 g of wet mycelia specifically bound 3.5 pmol of [3H]VB. The binding disappeared after pronase digestion and showed ligand specificity toward cis VB-C (cis VB-C greater than trans VB-C much greater than A-factor type), indicating that binding was due to a cis VB-C specific binding protein. Scatchard analysis of the binding demonstrated a single class of high affinity binding sites (Kd 1.1 nM) and low number of the binding sites (30-40 sites/genome DNA). By gel filtration on Sephadex G-75 and molecular sieve HPLC, the binding protein was shown to have an Mr of about 20,000. These results indicate that the substance is a novel VB-C binding protein and suggest that it is a VB-receptor mediating the pleiotropic signal transmitted by VBs in S. virginiae.

Oxidases involved in biosynthesis of macrolide antibiotic patulolides from Penicillium urticae S11R59

Patulolides are a group of 12-membered macrolide antibiotics produced by Penicillium urticae S11R59. An enzyme involved in the conversion of patulolide C to patulolide A was purified from P. urticae S11R59 and characterized. The enzyme showed a single band on SDS-PAGE and molecular sieve HPLC both of which indicated a Mr of 86,000, indicating that the enzyme is monomeric. However, the enzyme was separated into two bands of very similar pI's (pI 4.2 and 4.3) by isoelectric focusing. Both bands catalyzed the conversion of patulolide C to patulolide A, as demonstrated by activity staining. The two isoenzymes were proved to be oxidases by the simultaneous production of H2O2 during the conversion of patulolide C to patulolide A. The molar ratio for patulolides C, A and H2O2 was determined to be 1:1:1. The optimum pH and temperature were determined to be 7 and 35-40 degrees C, respectively, and the enzymes were stable at pH 6-9 and 4-40 degrees C. The oxidases showed characteristic absorption at 345 and 450 nm, indicating the presence of flavin as coenzyme. Among several analogues of patulolide C tested, the oxidases showed very narrow substrate-specificity; only patulolide C was oxidized to patulolide A. No enzyme activity for the reverse reaction, i.e. from patulolide A to patulolide C, was present in the cell-free extract of P. urticae S11R59. Patulolide C oxidases therefore play a key role in the biosynthesis of patulolides.

Structure-activity relationships of virginiae butanolide C, an inducer of virginiamycin production in Streptomyces virginiae

Virginiae butanolide C, [2-(1'-hydroxyhexyl)-3-(hydroxymethyl)butanolide (3)], is one of the inducers of virginiamycin production in Streptomyces virginiae. Various racemic analogues were synthesized, and their effectiveness in virginiamycin induction was studied. Among analogues having a series of C-2 side chains, those with 1'-hydroxyheptyl or 1'-hydroxyoctyl moiety were most effective with a minimum effective concentration of 0.8 ng/ml. At the same length of C-2 side chain, a 2,3-cis analogue was 10-fold more active than a 2,3-trans analogue, and the 2,3-trans analogue was 10-fold more active than an analogue having a 1'-ketoalkyl moiety at C-2 (A-factor type analogue). Methoxylation or deletion of either one of the two hydroxy groups in virginiae butanolide C analogues caused a 100 to 1,000-fold decrease in activity, thus indicating the importance of the two hydroxy groups in virginiamycin induction.