IM-2, a butyrolactone autoregulator,induces production of several nucleoside antibiotics in Streptomyces sp. FRI-5

IM-2 is one of the butyrolactone autoregulators of Streptomyces, which triggers production of a blue pigment in Streptomyces sp. FRI-5 at a concentration of 0.6 ng/ml. In the absence of IM-2, Streptomyces sp. FRI-5 was found to produce d-cycloserine. However, the addition of IM-2 at 5-h cultivation stopped both growth and d-cycloserine production, and instead induced production of several different antibiotics. The IM-2-induced antibiotics were isolated from the culture broth, and assigned as the nucleoside antibiotics, showdomycin and minimycin. Therefore, IM-2 was concluded to be a global regulator of a secondary metabolism, which not only induced the production of nucleoside antibiotics but also suppressed d-cycloserine production.     

Detection and properties of A-factor-binding protein from Streptomyces griseus.

The optically active form of tritium-labeled A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone), a pleiotropic autoregulator responsible for streptomycin production, streptomycin resistance, and sporulation in Streptomyces griseus, was chemically synthesized. By using the radioactive A-factor, a binding protein for A-factor was detected in the cytoplasmic fraction of this organism. The binding protein had an apparent molecular weight of approximately 26,000, as determined by gel filtration. Scatchard analysis suggested that A-factor bound the protein in the molar ratio of 1:1 with a binding constant, Kd, of 0.7 nM. The number of the binding protein was roughly estimated to be 37 per genome. The "inducing material" virginiae butanolide C (VB-C), which has a structure very similar to that of A-factor and is essential for virginiamycin production in Streptomyces virginiae, did not inhibit binding. In addition, no protein capable of specifically binding 3H-labeled VB-C was found in S. griseus. Together with the observation that VB-C had almost no biological activity on the restoration of streptomycin production or sporulation in an A-factor-deficient mutant of S. griseus, these results indicated that the binding protein had a strict ligand specificity. Examination for an A-factor-binding protein in Streptomyces coelicolor A3(2) and Streptomyces lividans showed the absence of any specifically binding protein.     

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.     

γ-Butyrolactone autoregulators and receptor proteins in non-<Emphasis Type="Italic">Streptomyces</Emphasis> actinomycetes producing commercially important secondary metabolites

The presence of -butyrolactone autoregulators and their receptor proteins were investigated in five representative strains of non-Streptomyces actinomycetes producing commercially important secondary metabolites. Ethyl acetate extracts of culture were assayed using wild-type S. virginiae for virginiae butanolide, S. lavendulae FRI-5 for IM-2, and S. griseus HH1 for A-factor. Actinoplanes teichomyceticus and Amycolatopsis mediterranei were shown to produce autoregulators. Corresponding autoregulator-binding activities were found in the crude cell-free lysates of these strains, using the binding assay with tritium-labeled autoregulator analogues as ligands, which suggests that non-Streptomyces actinomycetes might have autoregulator-dependent signaling cascades.     

The nusG gene of Streptomyces griseus: Cloning of the gene and analysis of the A-factor binding properties of the gene product

Abstract The nusG gene of Streptomyces griseus was cloned and the nucleotide sequence determined. It encodes a protein with an identify of 76% to the reported receptor (VbrA) for VB-C, an autoregulatory factor in Streptomyces virginae . NusG protein was expressed in Escherichia coli . However, no binding activity for A-factor, an butyrolactone autoregulator in S. griseus very similar to VB-C, could be detected. The nusG gene of S. griseus does not seem to encode the A-factor-binding protein.     

Optimum autoregulator addition strategy for maximum virginiamycin production in batch culture of Streptomyces virginiae

Virginiae butanolides (VBs) are autoregulators of Streptomyces virginiae, which induce virginiamycin biosynthesis. Generally, autoregulators are synthesized by the microorganism itself during culture. Addition of chemically synthesized virginiae butanolide-C (VB-C), which is one of the VBs, can also control the induction time and the amount of virginiamycin production. The optimum concentration and shot-feeding time of VB-C for the maximum production of virginiamycins M and S were investigated in flasks and jar-fermentor batch cultures. VB-C addition later than 8 h from the start of culture induced not only virginiamycin M and S synthesis but also VB synthesis. Virginiamycin M and S production increased with the decrease of total VBs (produced VBs and added VB-C) concentration. That is, although VBs are needed to induce virginiamycin M and S synthesis, the amount of VB-C added should be such that as small an amount as possible of VBs is synthesized to achieve the maximum production of virginiamycins M and S. However, the VB-C addition earlier than 8 h from the start of culture showed no clear relationship between the amounts of VBs and virginiamycins M and S produced. In conclusion, the maximum production of virginiamycins M and S was attained by the shot addition of 5 mug/L VB-C at 8 h from the start of culture. The maximum value was about twofold that without VB-C addition. The optimum addition strategy of VB-C was confirmed by the jar-fermentor experiments. (c) 1995 John Wiley & Sons, Inc.     

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.     

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.     

Stereospecific receptors for substance P on cultured human IM-9 lymphoblasts

The neuropeptide substance P (SP), which has been demonstrated to bind specifically to human blood T lymphocytes and to stimulate their uptake of [3H]thymidine and [3H]leucine, now is shown to bind stereospecifically to cultured human lymphoblasts of the IM-9 line. The specific binding of [3H]SP by IM-9 lymphoblasts increases linearly with the concentration of IM-9 lymphoblasts, achieves a plateau after approximately 15 to 20 min at 4 degrees C and 4 to 6 min at 37 degrees C, and is rapidly reversible at both 4 degrees C and 37 degrees C. The binding of [3H]SP at steady-state conditions demonstrates a dissociation constant (KD) of 0.65 +/- 0.19 nM (mean +/- SD, n = 5) and 22,641 +/- 6143 receptors per IM-9 lymphoblast. Maximal specific binding of [3H]SP to IM-9 lymphoblasts is observed at pH 7.4 and is dependent on the presence of Mg2+, but not Ca2+, in the medium. The peptide structural determinants of the inhibition of binding of [3H]SP to IM-9 lymphoblasts by substituent peptides and homologs of SP indicate that the receptors recognize predominantly the carboxy-terminal portion of SP. The characteristics of the interaction of SP with IM-9 lymphoblasts suggests a receptor-directed mechanism by which neuropeptides may modulate specifically the contributions of lymphocytes to immunity.     

Adenosine 3':5'-monophosphate-regulated phosphorylation of erythrocyte membrane proteins. Separation of membrane-associated cyclic adenosine 3':5'-monophosphate-dependent protein kinase from its endogenous substrates.

An adenosine 3':5'-monophosphate (cyclic AMP)-binding protein in the human erythrocyte plasma membrane was isotopically labeled using a photoaffinity analog of cyclic AMP, N6-(ethyl 2-diazomalonyl) cyclic [3H]AMP. The cyclic AMP-binding site is located in a polypeptide chain having a molecular weight of 48,000. Cyclic AMP-binding protein and cyclic AMP-dependent protein kinase were solubilized with 0.5% Triton X-100 in 56 mM sodium borate, pH 8, but 32P-labeled membrane phosphoproteins were retained in the Triton-insoluble fraction, suggesting that the membrane-associated binding protein is not a primary substrate for protein kinase. Triton-solubilized and membrane-associated protein kinase activities were stimulated 15- and 17-fold by cyclic AMP, suggesting that the degree of association between the catalytic anc cyclic AMP-binding components was very similar in both preparations. Fractionation and characterization of membrane phosphoproteins have shown that protein III and a co-migrating minor protein are substrates for protein kinase but membrane sialoglycoproteins are not phosphorylated.     

Molecular size of the 5-HT3 receptor solubilized from NCB 20 cells.

The 5-HT3 hydroxytryptamine receptor from NCB 20 cells was solubilized and the molecular and hydrodynamic properties of the receptor were investigated. The receptor was identified by binding of the radioligand 3-NN'-[3H]dimethyl-8-azabicyclo[3.2.1]octanyl indol-3-yl carboxylate ester [( 3H]Q ICS 205-930) to NCB 20 membranes (Bmax = 1.19 +/- 0.31 pmol/mg of protein; Kd = 0.43 +/- 0.076 nM) and was optimally solubilized with 0.5% deoxycholate. [3H]Q ICS 205-930 labelled one population of sites in solution (Bmax = 1.11 +/- 0.4 pmol/mg of protein; Kd = 0.48 +/- 0.06 nM; n = 4). The characteristics of [3H]Q ICS 205-930 binding were essentially unchanged by solubilization, and competition for [3H]Q ICS 205-930 binding by a series of 5-HT3 agonists and antagonists was consistent with binding to a 5-HT3 receptor site and was similar to that observed for 5-HT3 receptors solubilized from rat brain [McKernan, Quirk, Jackson & Ragan (1990) J. Neurochem. 54, 924-930]. Some physical properties of the solubilized receptor were investigated. The molecular size (Stokes radius) of the [3H]Q ICS 205-930-binding site was measured by gel-exclusion chromatography in a buffer containing 0.2% Lubrol and 0.5 M-NaCl and was determined as 4.81 +/- 0.15 nm (mean +/- S.E.M.; n = 6). Sucrose-density-gradient centrifugation was also performed under the same detergent and salt conditions to determine the partial specific volume (v) of the detergent-receptor site complex. This was found to be 0.794 ml.g-1. Sucrose-density-gradient centrifugation was carried out in both 1H2O and 2H2O to allow correction for detergent binding to the receptor. The Mr of the 5-HT3 receptor under these conditions was calculated as 249,000 +/- 18,000 (n = 3). The size and physical properties of the 5-HT3 receptor are similar to those observed for members of the family of ligand-gated ion channels.     

Characterization of thromboxane A2/prostaglandin H2 receptors and histamine H1 receptors in cultured guinea-pig tracheal smooth-muscle cells.

We characterized thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors and histamine H1 receptors in Guinea-pig cultured tracheal smooth-muscle cells (TSMC). [3H]SQ 29,548 (a TXA2 antagonist)-binding sites were saturable and a high affinity with a dissociation constant of 6.2 +/- 0.60 nM (mean +/- S.E.) and a receptor density of 46 +/- 4.6 fmol/10(6) cells. [3H]SQ 29548 binding was completely inhibited by TXA2 mimetics or antagonists. Intracellular calcium concentration ([Ca2+]i) in TSMC was increased with U46619 stimulation and the increase was attenuated by TXA2 antagonists, the potencies of which correlated with those inhibiting the activities of the [3H]SQ 29548 binding. [3H]Mepyramine (a H1 antagonist)-binding sites were also present in TSMC. [3H]Mepyramine had a single class of low-affinity-binding sites with a dissociation constant of 2.6 +/- 0.081 microM and a receptor density of 10.6 +/- 0.11 nmol/mg protein. [3H]Mepyramine binding in TSMC membrane was inhibited by H1 antagonists, but not by H2 antagonists. The inhibition constants of mepyramine in TSMC were 910-times lower than those in tracheal membranes. In contrast, the histamine-induced increase in [Ca2+]i in TSMC was inhibited in the presence of low concentrations of H1 antagonists. All these observations provide evidence that TXA2/PGH2 receptors, mepyramine-binding sites and/or H1 receptors are expressed in cultured TSMC.