Studies on the oxidation of p-aminobenzoate to p-nitrobenzoate by Streptomyces thioluteus

Streptomyces griseus: A new biocatalyst with N-oxygenase activity

Aromatic nitro compounds are key building blocks for many industrial syntheses and are also components of explosives, drugs and pesticides. Due to the environmentally unfriendly experimental conditions involved in their chemical syntheses, industrial processes would benefit from the use of biocatalysts. Among potentially useful enzymes, N-oxygenases, whose role is to oxygenate primary amines, are becoming relevant. These enzymes are involved in different secondary metabolic pathways in Streptomyces and in few other bacteria, forming part of the enzyme pools implicated in antibiotic synthesis. In this work, a group of Streptomyces strains, whose biomass was obtained from simple and novel culture media, were identified as new sources of N-oxygenase activity. Furthermore, the use of unspecific metabolic stimulation strategies allowed substantial improvements in the activity of whole cells as biocatalysts. It is remarkable the 6 to 50-fold increase in nitro compound yields compared to the biotransformation under standard conditions when Streptomyces griseus was the biocatalyst. In addition, biocatalyst substrate acceptance was studied in order to determine the biocatalytic potential of this enzyme.

Heteroatom-Heteroatom Bond Formation in Natural Product Biosynthesis

Natural products that contain functional groups with heteroatom-heteroatom linkages (X-X, where X = N, O, S, and P) are a small yet intriguing group of metabolites. The reactivity and diversity of these structural motifs has captured the interest of synthetic and biological chemists alike. Functional groups containing X-X bonds are found in all major classes of natural products and often impart significant biological activity. This review presents our current understanding of the biosynthetic logic and enzymatic chemistry involved in the construction of X-X bond containing functional groups within natural products. Elucidating and characterizing biosynthetic pathways that generate X-X bonds could both provide tools for biocatalysis and synthetic biology, as well as guide efforts to uncover new natural products containing these structural features.

Characterization of the N-oxygenase AurF from Streptomyces thioletus

AurF catalyzes the N-oxidation of p-aminobenzoic acid to p-nitrobenzoic acid in the biosynthesis of the antibiotic aureothin. Here we report the characterization of AurF under optimized conditions to explore its potential use in biocatalysis. The pH optimum of the enzyme was established to be 5.5 using phenazine methosulfate (PMS)/NADH as the enzyme mediator system, showing ~10-fold higher activity than previous reports in literature. Kinetic characterization at optimized conditions give a Km of 14.7 ± 1.1 μM, a kcat of 47.5 ± 5.4 min(-1) and a kcat/Km of 3.2 ± 0.4 μM(-1)min(-1). PMS/NADH and the native electron transfer proteins showed significant formation of the p-hydroxylaminobenzoic acid intermediate, however H2O2 produced mostly p-nitrobenzoic acid. Alanine scanning identified the role of important active site residues. The substrate specificity of AurF was examined and rationalized based on the protein crystal structure. Kinetic studies indicate that the Km is the main determinant of AurF activity toward alternative substrates.

Structure and Action of the N-oxygenase AurF from Streptomyces thioluteus

Nitro groups are found in a number of bioactive compounds. Most of them arise by a stepwise mono-oxygenation of amino groups. One of the involved enzymes is AurF participating in the biosynthesis of aureothin. Its structure was established at 2.1 A resolution showing a homodimer with a binuclear manganese cluster. The enzyme preparation, which yielded the analyzed crystals, showed activity using in vitro and in vivo assays. Chain fold and cluster are homologous with ribonucleotide reductase subunit R2 and related enzymes. The two manganese ions and an iron content of about 15% were established by anomalous X-ray diffraction. A comparison of the cluster with more common di-iron clusters suggested an additional histidine in the coordination sphere to cause the preference for manganese over iron. There is no oxo-bridge. The substrate p-amino-benzoate was modeled into the active center. The model is supported by mutant activity measurements. It shows the geometry of the reaction and explains the established substrate spectrum.

Para-position derivatives of fungal anthelmintic cyclodepsipeptides engineered with Streptomyces venezuelae antibiotic biosynthetic genes

PF1022A, a cyclooctadepsipeptide possessing strong anthelmintic properties and produced by the filamentous fungus Rosellinia sp. PF1022, consists of four alternating residues of N-methyl-L-leucine and four residues of D-lactate or D-phenyllactate. PF1022A derivatives obtained through modification of their benzene ring at the para-position with nitro or amino groups act as valuable starting materials for the synthesis of compounds with improved anthelmintic activities. Here we describe the production of such derivatives by fermentation through metabolic engineering of the PF1022A biosynthetic pathway in Rosellinia sp. PF1022. Three genes cloned from Streptomyces venezuelae, and required for the biosynthesis of p-aminophenylpyruvate from chorismate in the chloramphenicol biosynthetic pathway, were expressed in a chorismate mutase-deficient strain derived from Rosellinia sp. PF1022. Liquid chromatography-mass spectrometry and NMR analyses confirmed that this approach facilitated the production of PF1022A derivatives specifically modified at the para-position. This fermentation method is environmentally safe and can be used for the industrial scale production of PF1022A derivatives.

Synthetic studies toward SNF4435 C and SNF4435 D

[reaction: see text] A synthetic approach toward the immunosuppressants SNF3345 C and SNF4435 D featuring a tandem Stille coupling/electrocyclization cascade is described.

Mechanism of nitrification by Arthrobacter sp

Resting cells of Arthrobacter sp. excrete as much as 60 mug of hydroxylamine-nitrogen per ml when supplied with ammonium. An organic carbon source in abundant supply is necessary for the oxidation. Resting cells oxidize hydroxylamine to nitrite and 1-nitrosoethanol, the former accumulating only when an exogenous carbon source is available. Cell-free extracts contain an enzyme catalyzing the formation of hydroxylamine from acetohydroxamic acid, a hydroxylamine-nitrite oxido-reductase, and an enzyme producing nitrite and nitrate from various primary nitro compounds. Nitrite is not produced from hydroxylamine by the extracts, but 1-nitrosoethanol is formed from hydroxylamine in the presence of acetate. 1-Nitrosoethanol is also produced from acetohydroxamic acid by these preparations. Nitrite was formed from hydroxylamine, however, by extracellular enzymes excreted by the bacterium.