Narayan Prasad Niraula

Self-resistance mechanism in Streptomyces peucetius: Overexpression of drrA, drrB and drrC for doxorubicin enhancement

The resistance genes drrABC from Streptomyces peucetius ATCC 27952 were cloned into the pIBR25 expression vector under a strong ermE* promoter to enhance doxorubicin (DXR) production. The recombinant expression plasmids, pDrrAB25, pDrrC25 and pDrrABC25, were constructed to overexpress drrAB, drrC and drrABC, respectively, in S. peucetius ATCC 27952. The recombinant strains produced more DXR than the parental strain: a 2.2-fold increase with pDrrAB25, a 5.1-fold increase with pDrrC25, and a 2.4-fold increase with pDrrABC25. We also studied the relative ratios of doxorubicin, daunorubicin and epsilon-rhodomycinone produced in these recombinant strains.

Biotechnological doxorubicin production: pathway and regulation engineering of strains for enhanced production

Doxorubicin (DXR) is an anthracycline-type polyketide, typically produced by Streptomyces peucetius ATCC 27952. Like the biosynthesis of other secondary metabolites in Streptomyces species, DXR biosynthesis is tightly regulated, and a very low level of DXR production is maintained in the wild-type strain. Despite that DXR is one of the most broadly used and clinically important anticancer drugs, a traditional strain improvement strategy has long been practiced via recursive random mutagenesis, with little understanding of the molecular genetic basis underlying such enhanced DXR production. Since DXR titer enhancement is imperative in the fermentation industry, attaining a comprehensive understanding and its application of the specific regulatory systems that govern secondary metabolite production is an important aspect of metabolic engineering that can efficiently improve fermentation titers. In this mini-review, various efforts to improve the titers of DXR have been summarized based on biosynthetic and regulatory studies including transcriptional and product analyses.

Limitations in doxorubicin production from Streptomyces peucetius.

Doxorubicin (DXR), produced by Streptomyces peucetius ATCC 27952, exhibits potent antitumor activity against various cancer cell lines. Considerable time has lapsed since the biosynthesis of DXR and its overproduction was first summarized. Based on biosynthetic studies and product analysis, various factors affecting its production by the parental strain, S. peucetius ATCC 27952, are reviewed to better circumvent any bottlenecks in DXR production, thereby providing ideas to genetically engineered industrial strains of S. peucetius.

Improvement in doxorubicin productivity by overexpression of regulatory genes in Streptomyces peucetius

Biosynthesis of doxorubicin (DXR) is tightly regulated, limiting its production in Streptomyces peucetius cultures. The regulatory genes dnrN, dnrI, afsR, and metK1-sp from S. peucetius ATCC 27952 were cloned into the pIBR25 expression vector under the control of the strong ermE* promoter to enhance DXR production. The constructed expression plasmids, pNI25 (with dnrN-dnrI), pNIS25 (with dnrN-dnrI-metK1-sp), pNIR25 (with dnrN-dnrI-afsR), pRS25 (with afsR-metK1-sp) and pNIRS25 (with dnrN-dnrI-afsR-metK1-sp), were transformed into S. peucetius. The recombinant strains NI, NIS and NIR produced greater amounts of DXR than the parental strain with an increment of 1.2-fold by pNI25, 1.4-fold by pNIS25 and 4.3-fold by pNIR25, whereas pRS25 and pNIRS25 had no significant effect on DXR production. We also studied the transcriptional level of overexpressed regulatory genes and relative production of DXR, daunorubicin (DNR) and epsilon-rhodomycinone (RHO) in each recombinant strain.

Enhancement of doxorubicin production by expression of structural sugar biosynthesis and glycosyltransferase genes in Streptomyces peucetius

To enhance doxorubicin (DXR) production, the structural sugar biosynthesis genes desIII and desIV from Streptomyces venezuelae ATCC 15439 and the glycosyltransferase pair dnrS/dnrQ from Streptomyces peucetius ATCC 27952 were cloned into the expression vector pIBR25, which contains a strong ermE promoter. The recombinant plasmids pDnrS25 and pDnrQS25 were constructed for overexpression of dnrS and the dnrS/dnrQ pair, whereas pDesSD25 and pDesQS25 were constructed to express desIII/desIV and dnrS/dnrQ-desIII/desIV, respectively. All of these recombinant plasmids were introduced into S. peucetius ATCC 27952. The recombinant strains produced more DXR than the S. peucetius parental strain: a 1.2-fold increase with pDnrS25, a 2.8-fold increase with pDnrQS25, a 2.6-fold increase with pDesSD25, and a 5.6-fold increase with pDesQS25. This study showed that DXR production was significantly enhanced by overexpression of potential biosynthetic sugar genes and glycosyltransferase.

Identification of the duplicated genes for S‐adenosyl‐l‐methionine synthetase (metK1‐sp and metK2‐sp) in Streptomyces peucetius var. caesius ATCC 27952

Aims:  To characterize the function of both metK1‐sp (sp1190) and metK2‐sp (sp1566) in vitro and in vivo, and to study the regulation of doxorubicin production by overexpressing the metK.

Superoxide dismutase (SOD) genes in Streptomyces peucetius: Effects of SODs on secondary metabolites production

Two superoxide dismutase (SOD) genes; sod1 and sod2, from Streptomyces peucetius ATCC 27952 show high similarity to other known SODs from Streptomyces coelicolor A3(2) and Streptomyces avermitilis MA-4680. These sod1 and sod2 were cloned into pIBR25 expression vector under a strong ermE* promoter to enhance secondary metabolites from Streptomyces strains. The recombinant expression plasmids; pIBR25SD1 and pIBR25SD2, were constructed to overexpress sod1 and sod2 respectively to enhance production of doxorubicin (DXR) in S. peucetius, clavulanic acid (CA) in Streptomyces clavuligerus NRRL 3585 and actinorhodin (ACT) and undecylprodigiosin (Red) in Streptomyces lividans TK24. Biomass variation, antibiotics production and transcriptional analysis of regulatory genes in recombinant strains have been studied to understand the effect of sod1 and sod2. The cell growth analysis shows that life span of all recombinant strains was found to be elevated as compared to wild type cells. In S. peucetius, overexpression of sod1 and sod2 was not effective in DXR production but in case of S. clavuligerus, CA production was increased by 2.5 and 1.5 times in sod1 and sod2 overexpression, respectively while in case of S. lividans, ACT production was increased by 1.4 and 1.6 times and Red production by 1.5 and 1.2 times upon sod1 and sod2 overexpressions, respectively as compared to the corresponding wild type strains.

Hydrogen peroxide-mediated dealkylation of 7-ethoxycoumarin by cytochrome P450 (CYP107AJ1) from Streptomyces peucetius ATCC27952

Cytochrome P450 CYP107AJ1, which was isolated from Streptomyces peucetius and showed high homology with peroxygenases, catalyzed a dealkylation reaction with hydrogen peroxide to provide electrons, protons and oxygen, evading the requirement for a supporting redox protein. Preliminary investigation of its transcriptional level in S. peucetius showed significant expression. Homology modeling and subsequent docking with 7-ethoxycoumarin yielded a reasonable docked structure. cyp107AJ1 cloned into pET28a(+) was expressed in Escherichia coli, and soluble protein was subjected to column-chromatographic purification in order to carry out enzyme assays with 7-ethoxycoumarin. HPLC analysis of the extracted product, corresponding to its LC/MS analysis, showed the dealkylated 7-ethoxycoumarin, which was further established by subsequent GC/MS spectral analysis. We suggest that CYP107AJ1 bypassed the requirement for NAD(P)H and redox partners for generating novel analogues.

Identification and characterization of a NADH oxidoreductase involved in phenylacetic acid degradation pathway from Streptomyces peucetius.

Annotation of genome of Streptomyces peucetius revealed a putative phenylacetic acid degradation NADH oxidoreductase. RT-PCR analysis of the gene readily showed notable transcription in its native state. The transcription level of paaE when the host is grown on phenylacetic acid showed increased transcription. paaE was cloned into a pET32a(+) vector to overexpress the protein coupled with fusion tags in Escherichia coli BL21(DE3) and purified by immobilized metal affinity chromatography using His-tag. The flavin released from heat-denatured PaaE was identical to that of authentic FAD in HPLC analysis. The purified protein efficiently reduced p-nitroblue tetrazolium (an electron acceptor) in presence of NADH. Cell growth analysis of S. peucetius in phenylacetic acid evidently revealed its involvement in degradation of phenylacetic acid - a key environmental pollutant.

In-silico and In-vitro based studies of Streptomyces peucetius CYP107N3 for oleic acid epoxidation.

Certain members of the cytochromes P450 superfamily metabolize polyunsaturated long-chain fatty acids to several classes of oxygenated metabolites. An approach based on in silico analysis predicted that Streptomyces peucetius CYP107N3 might be a fatty acid-metabolizing enzyme, showing high homology with epoxidase enzymes. Homology modeling and docking studies of CYP107N3 showed that oleic acid can fit directly into the active site pocket of the double bond of oleic acid within optimum distance of 4.6 Å from the Fe. In order to confirm the epoxidation activity proposed by in silico analysis, a gene coding CYP107N3 was expressed in Escherichia coli. The purified CYP107N3 was shown to catalyze C9-C10 epoxidation of oleic acid in vitro to 9,10-epoxy stearic acid confirmed by ESI-MS, HPLC-MS and GC-MS spectral analysis. [BMB Reports 2012; 45(12): 736-741]