Controlled biosynthesis of actinomycin with sarcosine

RNase III is required for actinomycin production in Streptomyces antibioticus

Using insertional mutagenesis, we have disrupted the RNase III gene, rnc, of the actinomycin-producing streptomycete, Streptomyces antibioticus. Disruption was verified by Southern blotting. The resulting strain grows more vigorously than its parent on actinomycin production medium but produces significantly lower levels of actinomycin. Complementation of the rnc disruption with the wild-type rnc gene from S. antibioticus restored actinomycin production to nearly wild-type levels. Western blotting experiments demonstrated that the disruptant did not produce full-length or truncated forms of RNase III. Thus, as is the case in Streptomyces coelicolor, RNase III is required for antibiotic production in S. antibioticus. No differences in the chemical half-lives of bulk mRNA were observed in a comparison of the S. antibioticus rnc mutant and its parental strain.

Production of actinomycin-D by the mutant of a new isolate of Streptomyces sindenensis

An actinomycin-D producing strain was isolated from soil and characterized as Streptomyces sindenensis. The culture was subjected to UV irradiation and a mutant with 400% higher actinomycin-D production was isolated (400 mg/l^-1 as compared to 80 mg/l^-1 produced by the parent). Production medium was optimized and antibiotic yield with the mutant was enhanced to 850 mg/l^-1 which is 963% higher as compared with the parent.

Structure of Phenoxazinone Synthase from Streptomyces antibioticus Reveals a New Type 2 Copper Center,

The multicopper oxidase phenoxazinone synthase (PHS) catalyzes the penultimate step in the biosynthesis of the antibiotic actinomycin D by Streptomyces antibioticus. PHS exists in two oligomeric forms: a dimeric form and a hexameric form, with older actinomycin-producing cultures containing predominately the hexameric form. The structure of hexameric PHS has been determined using X-ray diffraction to a resolution limit of 2.30 A and is found to contain several unexpected and distinctive features. The structure forms a hexameric ring that is centered on a pseudo 6-fold axis and has an outer diameter of 185 A with a large central cavity that has a diameter of 50 A. This hexameric structure is stabilized by a long loop connecting two domains; bound to this long loop is a fifth copper atom that is present as a type 2 copper. This copper atom is not present in any other multicopper oxidase, and its presence appears to stabilize the hexameric structure.

Role of valine and isoleucine as regulators of actinomycin peptide formation by Streptomyces chrysomallus

Katz, Edward (Rutgers, The State University, New Brunswick, N. J.), Clarence R. Waldron, and Mary Lou Meloni. Role of valine and isoleucine as regulators of actinomycin peptide formation by Streptomyces chrysomallus. J. Bacteriol. 82:600-608. 1961-d-Valine is an effective inhibitor of actinomycin synthesis by Streptomyces chrysomallus; l-valine stimulates actinomycin production and reverses the inhibition due to the d-enantiomorph. The incorporation of l-valine into the medium results, particularly, in a marked increase in actinomycin IV formation. In studies with various isoleucine isomers it was shown that l-isoleucine enhances actinomycin VII production; the principal effect of d-alloisoleucine and, especially, d-isoleucine, is to bring about synthesis of two new actinomycins which contain N-methylisoleucine. Both l- and d-threonine were observed to have an effect similar to that obtained with l-isoleucine. An interpretation of these findings has been discussed.

Intramolecular interactions, mesomerism and dynamics in actinomycin D studied by 15N NMR spectroscopy

We present a detailed conformational study of 15N-labelled actinomycin D in different organic solvents using 1H, 15N and two-dimensional (2D) NMR techniques at 30.4 MHz and 50.6 MHz. The assignment of the threonine and valine 15N resonances to the individual residues on the alpha- or beta-lactone rings was achieved via heteronuclear shift-correlated 2D NMR experiments. The solvent perturbation studies allow an estimation of the solvent accessibility of the nitrogens and carbonyl groups. Evidence is presented that the pentapeptide rings of actinomycin D have different conformations in polar and in apolar solvents. The chromophoric N10 is efficiently solvent-protected, the solvent-dependence of its 15N resonance resulting from solvent interactions at other positions of the molecule and from solvent-dependent changes in the twisting of the chromophoric system. The chromophoric 2-amino nitrogen is shown to exhibit a strong sp2 character due to the formation of a conjugated system with the carbonyl group at C1. Such a conjugation requires a non-planar chromophoric ring system. Additionally, a hydrogen bond connecting the 2-amino and the 1-carbonyl group was detected. In some solvents, two resonances appear for the 2-amino nitrogen implying the presence of the 2-amino group in two different conformations. The possible implications of the non-planarity of the chromophore for the intercalation process and for the biological activity of the drug are discussed.

The nucleotide sequence of the tyrosinase gene from Streptomyces antibioticus and characterization of the gene product

The sequence of a 1.56-kb DNA fragment containing the tyrosinase gene (mel) from Streptomyces antibioticus was determined and the Mr (30612) and amino acid (aa) sequence of the protein were deduced from the nucleotide (nt) sequence. Intracellular and extracellular tyrosinase from S. antibioticus, transformed with pIJ702 (containing mel), were purified to homogeneity; the Mr (29 500), as determined by Sephadex G-75 chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), was consistent with the value derived from the nt sequence. Edman degradation established that the N-terminal sequence of both the intracellular and extracellular forms of tyrosinase are identical and correspond to the aa sequence derived from the structural gene. In addition, this sequence exhibits striking homology to the N-terminal region of the intracellular and extracellular enzyme purified from Streptomyces glaucescens (Crameri et al., 1982). An additional open reading frame (ORF438) upstream of the mel gene, was also identified that appears to code for a protein (Mr = 14 754) with a putative signal sequence.

Control of the actinomycin biosynthetic pathway in and actinomycin resistance of Streptomyces spp

Using actinomycin-producing and nonproducing strains of Streptomyces antibioticus, I studied several steps in the biosynthetic pathway of this antibiotic. Actinomycin-nonproducing strains derived after acriflavine or novobiocin treatment showed activity of kynurenine formamidase and phenoxazinone synthase as high as that of the parental strain, but these nonproducing strains failed to convert 4-methyl-3-hydroxy-anthranilic acid to actinomycin. In addition, accumulation of 4-methyl-3-hydroxyanthranilic acid (in the presence of D-valine) was not detected in the nonproducing isolates. Actinomycin-nonproducing strains derived after acriflavine treatment of Streptomyces parvulus showed a drastic decrease of resistance to the antibiotic. However these strains regained resistance after preincubation with a small amount of actinomycin D.

High-frequency fusion of Streptomyces parvulus or Streptomyces antibioticus protoplasts induced by polyethylene glycol

Conditions were established for the regeneration of protoplasts of Streptomyces parvulus and Streptomyces antibioticus to the mycelial form. Regeneration was accomplished with a hypertonic medium that contained sucrose, CaCl2, MgCl2, and low levels of phosphate. High-frequency fusion of protoplasts derived from auxotrophic strains of S. parvulus or S. antibioticus was induced by polyethylene glycol 4,000 (42%, wt/vol). The frequency of genetic transfer by the fusogenic procedure varied with the auxotrophic strains examined. Fusion with auxotrophic strains of S. parvulus resulted in the formation of true prototrophic recombinants. Similar studies with S. antibioticus revealed that both stable prototrophic recombinants and heterokaryons were formed.

Glutamate-induced uptake of proline by Streptomyces antibioticus

Streptomyces antibioticus possesses an energy-dependent, carrier mediated transport system for the uptake of L-glutamate and L-proline. Amino acid transport was found to have a temperature optimum of 35 degrees C and a pH optimum from 7.0 to 8.0 for glutamate and 6.5 to 7.5 for proline uptake. Uptake did not depend upon Mg2+, Ca2+, Zn2+, Na+, or Fe2+ ions. Reversible p-hydroxymercuribenzoate inhibition of uptake indicated the involvement of an active sulfhydryl group. L-Glutamate uptake was mediated by a glutamate-inducible, nonspecific transport system, which was extremely stable and was not subject to substrate inhibition by L-proline. On the other hand, L-proline transport was mediated by at least two systems. The L-glutamate-inducible nonspecific system can account for uptake of proline by the mycelium grown in glutamate. In addition, a proline-specific, constitutive transport system was found to be present in the mycelium grown in organic and inorganic nitrogen sources other than L-glutamate. Shift experiments revealed that proline transport is not as stable as glutamate transport when the glutamate-inducible nonspecific system is utilized.

Development of a chemically defined medium for the synthesis of actinomycin D by Streptomyces parvulus

A chemically defined medium, consisting of d-fructose, l-glutamic acid, l-histidine, K(2)HPO(4), MgSO(4).7H(2)O, ZnSO(4).7H(2)O, CaCl(2).2H(2)O, FeSO(4).7H(2)O, CoCl(2).6H(2)O, and deionized water, was developed for synthesis of high yields (500 to 600 mug/ml) of actinomycin D by Streptomyces parvulus. Under these nutritional conditions, growth and actinomycin formation did not follow a typical trophophase-idiophase pattern. The amino acids appeared to have a sparing action on the utilization of d-fructose which was slowly and incompletely metabolized during mycelium development and antibiotic production. A significant repression of actinomycin synthesis by S. parvulus was observed when d-glucose (0.01 to 0.25%) was added to the culture medium. The repression was not due to a decline in the pH of the medium during glucose catabolism.

Biogenetic origin of the D-isoleucine and N-methyl-L-alloisoleucine residues in the actinomycins

Studies with (14)C-labeled isoleucine stereisomers have established that l-alloisoleucine, d-alloisoleucine, and d-isoleucine may function as precursors for the biogenesis of d-isoleucine and N-methyl-l-alloisoleucine residues in actinomycin. l-[(14)C]isoleucine appears to be employed chiefly for d-alloisoleucine (and N-methylisoleucine [?] formation); however, its role in the biosynthesis of d-isoleucine and N-methylalloisoleucine remains unclear. The potential pathway of biosynthesis of d-isoleucine and N-methyl-l-isoleucine is discussed.

Production, isolation, and properties of azetomycins

Streptomyces antibioticus synthesizes five actinomycins that differ in the "proline site" of the molecule. When cultured in the presence of azetidine-2-carboxylic acid (AzC), antibiotic synthesis was stimulated 40 to 50%, synthesis of actinomycin IV was inhibited, and one or both prolines were replaced by AzC. AzC incorporation could not be reversed by concomitant supplementation with proline or sarcosine, and only pipecolic acid affected a minor reversal of AzC incorporation. AzC-containing actinomycins were isolated and designated azet-I and azet-II; a third unresolved component or mixture was called azet-III. The molar ratio of AzC to proline was: azet-I, 1:1; azet-II, 2:0. Azet-III was equivocal. These azetidine actinomycins (azetomycins) were found to be potently inhibitory to the growth of selected gram-positive but not as potent to the growth of gram-negative organisms. The relative inhibitory affect against growth and ribonucleic acid synthesis in Bacillus subtilis was: actinomycin IV =/> azet-I > azet-II >>> azet-III. Protein synthesis was affected similarly; however, kinetic studies with B. subtilis revealed that ribonucleic acid synthesis was inhibited rapidly followed by an inhibition of protein synthesis. At concentrations less than 1 mug/ml, deoxyribonucleic acid synthesis was stimulated by these actinomycins.

Branched-chain amino acid substitutions in the biosynthesis of the antibiotic actinomycin

Actinomycins normally contain N-methyl-l-valine and either d-valine, d-alloisoleucine or both amino acids in the molecule. During antibiotic formation in a medium supplemented with one of the four isoleucine stereoisomers, Streptomyces parvulus and S. chrysomallus form complex actinomycin mixtures (C(1), C(2), C(3), E(1), and E(2)-like compounds). Although chromatographic techniques suggested that single homogeneous components had been isolated, subsequent studies indicated that such chromatographic fractions probably consisted of multiple isomers of actinomycin. Amino acid analyses revealed the presence of N-methylvaline and/or N-methylalloisoleucine and, in addition, d-isoleucine, d-valine, and d-alloisoleucine were frequently found in a given fraction.

Effect of pipecolic acid isomers on the biogenesis of actinomycins

Streptomyces antibioticus produces a family of actinomycin components which differ solely at the "imino acid" site of the molecule; however, new congeners of actinomycin are synthesized when cultures are supplemented with pipecolic acid (PA). The quantitative and qualitative nature of the actinomycins produced differed when cultures were incubated in the presence of either l-, d-, or racemic PA. In the presence of d-PA, the quantitative and qualitative nature of those actinomycins produced were similar to those produced in the absence of supplementation. By contrast, in the presence of l-PA or dl-PA new actinomycin components containing PA were synthesized at the expense of normally produced components. Also, the total amount of antibiotic produced decreased in response to increasing concentrations of exogenously supplied l-PA. This effect occurred whether or not d-PA was also added to cultures. Concentrations of l-PA greater than 125 mug/ml of medium resulted in no additional decrease in the amount of antibiotic produced. Although PA-containing actinomycins were formed as early as 6 h after the addition of 250 mug of l-PA per ml, it was not until 24 h postaddition that the relative percentages of actinomycin components produced approached a constant value. Evidence presented here indicated that the l-isomer of PA replaces l-proline in the pentapeptide of actinomycin.

Regulation of secondary metabolite biosynthesis: catabolite repression of phenoxazinone synthase and actinomycin formation by glucose

Synthesis of the secondary metabolite, actinomycin, and the enzyme, phenoxazinone synthase, involved in the biosynthesis of the antibiotic, were shown to be under severe catabolite repression by glucose. Of a variety of hexoses and carbon compounds examined, glucose, and to a lesser extent, mannose, proved to be the most repressive for enzyme synthesis. The repression by glucose was most evident before production of the antibiotic. In a chemically defined medium suitable for actinomycin production, synthesis of phenoxazinone synthase began at the time the glucose (0.1%) supply was depleted. Soon after, antibiotic synthesis was initiated. Galactose, the major carbon source for growth and antibiotic synthesis, was not utilized until the glucose was consumed. Generally, carbon compounds which supported a rapid rate of growth were most effective in producing catabolite repression.

Actinomycin analogues containing pipecolic acid: relationship of structure to biological activity

Streptomyces antibioticus synthesizes a mixture of actinomycins which differ at the "imino acid" site of the peptide chains. In the presence of exogenous pipecolic acid, several new actinomycins were synthesized and 70% of the proline in the antibiotic mixture was replaced by the analogue. Three new antibiotics (designated Pip 1alpha, Pip 1beta, and Pip 2) were isolated from culture filtrates, purified, and crystallized. The molar ratio of pipecolic acid to proline was: Pip 1alpha, 1:0; Pip 1beta, 1:1; Pip 2, 2:0. These compounds inhibited the growth and cell division of gram-positive, but not gram-negative, bacteria. The relative inhibitory activity against bacteria, Escherichia coli deoxyribonucleic acid (DNA)-dependent ribonucleic acid (RNA) polymerase in vitro, and RNA synthesis in Bacillus subtilis and mouse L-929 cells was: actinomycin IV = Pip 1beta > Pip 2 > Pip 1alpha. Protein synthesis in B. subtilis was less affected, and DNA synthesis was inhibited only at higher concentrations of antibiotic tested. In L cells, DNA formation was reduced less than RNA synthesis, whereas protein synthesis was not blocked under the experimental conditions employed. Kinetic studies with B. subtilis revealed that RNA synthesis was inhibited rapidly followed by an inhibition of protein synthesis. All four antibiotics markedly inhibited the replication of vaccinia virus and reovirus in tissue culture cells, but the production of poliovirus was resistant to the antibiotics. These actinomycins bind to DNA, resulting in an elevation of its T(m) and a decrease in the peak extinction of the actinomycins. The mode of action, as well as the structure-activity relationships among the actinomycins, are discussed relative to a previously proposed model of binding.

Effect of structural and stereochemical methylproline isomers on actinomycin biosynthesis

The inhibitory effect of methylprolines on actinomycin biosynthesis by Streptomyces antibioticus was studied; the order of effectiveness was 3- >4- >5-methyl-dl-proline. Cis-3-methyl-dl-proline was 14 times more active than the trans isomer. It was also found that 4- and, possibly, 5-methylproline were incorporated into the actinomycin molecule. When 4-methylproline was present, three new actinomycins, representing 50 to 60% of the antibiotic mixture, were synthesized. Growth of the organism may be stimulated at concentrations (0.1 to 1.0 mug per ml) of 3-methylproline that inhibit antibiotic formation, thus providing additional evidence for a different mechanism of actinomycin synthesis from that of protein synthesis. Azetidine-2-carboxylic acid, piperdine-2-carboxylic acid, and hydroxyproline (but not sarcosine) reversed the inhibition due to 3-methylproline.

Origin of the sarcosine molecules of actinomycins

1. Streptomyces V-187 produces on minimal medium a mixture composed mainly of actinomycin C(1) (actinomycin D) and actinomycin A(1) (actinomycin I). If sarcosine is added to the medium, the micro-organism produces, in addition to actinomycins C(1) and A(1), actinomycin F(8) (actinomycin II) and actinomycin F(9) (actinomycin (III), characterized by the substitution by sarcosine of one or both the proline molecules present in actinomycin C(1). 2. Exogenous sarcosine seems to be incorporated as such by Streptomyces V-187 only in the sarcosine molecule(s) that replace proline in the actinomycins of the F group, whereas, for the synthesis of the other sarcosine molecules, the amino acid is first demethylated to glycine. 3. The incorporation of sarcosine and glycine into actinomycin by Streptomyces antibioticus appears to follow a similar pattern, except that a portion of the methyl group produced in the degradation of sarcosine is utilized as a source of the methyl groups of the antibiotic. This explains the previously reported lack of cross-dilution between glycine and sarcosine observed in the incorporation of these amino acids into actinomycin.