Accumulation of 6-deoxyerythronolide B in a normal strain of Streptomyces erythreus and hydroxylation at carbon 6 of the erythranolide ring system by a soluble noninduced cell-free enzyme system

Cloning and heterologous expression of the genes encoding nonspecific electron transport components for a cytochrome P450 system of Saccharopolyspora erythraea involved in erythromycin production

The forA gene encoding a protein that can function as a NADH:ferredoxin oxidoreductase (For) has been cloned from Saccharopolyspora erythraea, the erythromycin A (ErA) producer. In a previous study For protein, together with the FdxA ferredoxin from the same organism, was shown to be able to reconstitute the cytochrome P450 system responsible for the hydroxylation of 6-deoxyerythronolide B, an intermediate of ErA biosynthesis. Nucleotide sequence data suggest that the cloned forA gene codes for For, the putative pyruvate dehydrogenase component, dihydrolipoamide dehydrogenase, or its close homolog. Overexpression of forA appeared to be toxic to Escherichia coli.

Characterization of Saccharopolyspora erythraea cytochrome P-450 genes and enzymes, including 6-deoxyerythronolide B hydroxylase

Previous studies of erythromycin biosynthesis have indicated that a cytochrome P-450 monooxygenase system is responsible for hydroxylation of 6-deoxyerythronolide B to erythronolide B as part of erythromycin biosynthesis in Saccharopolyspora erythraea (A. Shafiee and C. R. Hutchinson, Biochemistry 26:6204-6210 1987). The enzyme was previously purified to apparent homogeneity and found to have a catalytic turnover number of approximately 10(-3) min-1. More recently, disruption of a P-450-encoding sequence (eryF) in the region of ermE, the erythromycin resistance gene of S. erythraea, produced a 6-deoxyerythronolide B hydroxylation-deficient mutant (J. M. Weber, J. O. Leung, S. J. Swanson, K. B. Idler, and J. B. McAlpine, Science 252:114-116, 1991). In this study we purified the catalytically active cytochrome P-450 fraction from S. erythraea and found by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis that it consists of a major and a minor P-450 species. The gene encoding the major species (orf405) was cloned from genomic DNA and found to be distinct from eryF. Both the orf405 and eryF genes were expressed in Escherichia coli, and the properties of the proteins were compared. Heterologously expressed EryF and Orf405 both reacted with antisera prepared against the 6-deoxyerythronolide B hydroxylase described by Shafiee and Hutchinson (1987), and the EryF polypeptide comigrated with the minor P-450 species from S. erythraea on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels. In comparisons of enzymatic activity, EryF hydroxylated a substrate with a turnover number of 53 min-1, whereas Orf405 showed no detectable activity with a 6-deoxyerythronolide B analog. Both enzymes showed weak activity in the O-dealkylation of 7-ethoxycoumarin. We conclude that the previously isolated 6-deoxyerythronolide B hydroxylase was a mixture of two P-450 enzymes and that only the minor form shows 6-deoxyerythronolide B hydroxylase activity.

Purification and reconstitution of the electron transport components for 6-deoxyerythronolide B hydroxylase, a cytochrome P-450 enzyme of macrolide antibiotic (erythromycin) biosynthesis

The hydroxylation of 6-deoxyerythronolide B (6D) to erythronolide B, a step in the biosynthesis of the 14-membered macrolide antibiotic erythromycin A by Saccharopolyspora erythraea, is catalyzed by a cytochrome P-450 monooxygenase that requires two electron transport proteins for the function of this terminal hydroxylase (A. Shafiee and C. R. Hutchinson, Biochemistry 26:6204-6210, 1987). Two flavoproteins and an iron-sulfur protein (erythrodoxin) were purified from S. erythraea CA340 and shown to act with 6D hydroxylase to catalyze the hydroxylation of (9R)-[9-3H]9-deoxo-9-hydroxy-6D in vitro in a suitably reconstituted system. The flavoproteins contained flavin adenine dinucleotide and exhibited characteristic absorption maxima at 356 and 456 nm. The one with an Mr of 47,000 showed NADPH-dependent diaphorase and cytochrome c reductase activity, and the other, with an Mr of 53,000 showed NADH-dependent activities of the same two types. Erythrodoxin contained acid-labile sulfur and iron, had an Mr of 27,500, and showed a broad absorption maximum between 394 and 404 nm. The sequence of its first 15 amino acids, except for position 12, was the same as that of the ferredoxin from Mycobacterium smegmatis.

Induction of cytochrome P-450-dependent sulfonylurea metabolism in Streptomyces griseolus

Inducible cometabolism of several sulfonylurea herbicides by Streptomyces griseolus has been shown to occur by hydroxylation, O-dealkylation, or deesterification reactions. Only after growth of the bacterium in the presence of sulfonylurea did cell-free extracts exhibit NAD(P)H-dependent sulfonylurea metabolism. These extracts were shown to contain elevated levels of soluble cytochrome P-450 and exhibit sulfonylurea induced difference spectra consistent with binding of substrate to cytochrome(s) P-450. These results establish the presence of an inducible cytochrome P-450-dependent sulfonylurea metabolizing system in S. griseolus.

Enzymes of secondary metabolism and the biosynthesis of macrolide antibiotics

Enzymes participating in the biosynthesis of macrolide antibiotics are reviewed. Enzyme activities are known to play a pivotal role in the formation of biologically active compounds. Hence it is essential to understand these enzymes, their properties and regulation. Macrolide antibiotics represent a relatively compact group of natural products and include several excellent model compounds suitable for enzyme studies that could be generalized to other oligoketide antibiotics.

Demethylation of Veratrole by Cytochrome P-450 in Streptomyces setonii

The actinomycete Streptomyces setonii 75Vi2 demethylates vanillic acid and guaiacol to protocatechuic acid and catechol, respectively, and then metabolizes the products by the β-ketoadipate pathway. UV spectroscopy showed that this strain could also metabolize veratrole (1,2-dimethoxybenzene). When grown in veratrole-containing media supplemented with 2,2′-dipyridyl to inhibit cleavage of the aromatic ring, S. setonii accumulated catechol, which was detected by both liquid chromatography and gas chromatography. Reduced cell extracts from veratrole-grown cultures, but not sodium succinate-grown cultures, produced a carbon monoxide difference spectrum with a peak at 450 nm that indicated the presence of soluble cytochrome P-450. Addition of veratrole or guaiacol to oxidized cell extracts from veratrole-grown cultures produced difference spectra that indicated that these compounds were substrates for cytochrome P-450. My results suggest that S. setonii produces a cytochrome P-450 that is involved in the demethylation of veratrole and guaiacol to catechol, which is then catabolized by the β-ketoadipate pathway.