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Mirzaei PA, Moshfeghi M, Motamedi H, Sheikhnejad Y, Bordbar H. A simplified tempo-spatial model to predict airborne pathogen release risk in enclosed spaces: An Eulerian-Lagrangian CFD approach. Build Environ 2022; 207:108428. [PMID: 34658495 PMCID: PMC8511599 DOI: 10.1016/j.buildenv.2021.108428] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Revised: 10/05/2021] [Accepted: 10/05/2021] [Indexed: 05/19/2023]
Abstract
COVID19 pathogens are primarily transmitted via airborne respiratory droplets expelled from infected bio-sources. However, there is a lack of simplified accurate source models that can represent the airborne release to be utilized in the safe-social distancing measures and ventilation design of buildings. Although computational fluid dynamics (CFD) can provide accurate models of airborne disease transmissions, they are computationally expensive. Thus, this study proposes an innovative framework that benefits from a series of relatively accurate CFD simulations to first generate a dataset of respiratory events and then to develop a simplified source model. The dataset has been generated based on key clinical parameters (i.e., the velocity of droplet release) and environmental factors (i.e., room temperature and relative humidity) in the droplet release modes. An Eulerian CFD model is first validated against experimental data and then interlinked with a Lagrangian CFD model to simulate trajectory and evaporation of numerous droplets in various sizes (0.1 μm-700 μm). A risk assessment model previously developed by the authors is then applied to the simulation cases to identify the horizontal and vertical spread lengths (risk cloud) of viruses in each case within an exposure time. Eventually, an artificial neural network-based model is fitted to the spread lengths to develop the simplified predictive source model. The results identify three main regimes of risk clouds, which can be fairly predicted by the ANN model.
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Affiliation(s)
- P A Mirzaei
- Architecture & Built Environment Department, University of Nottingham, University Park, Nottingham, UK
| | - M Moshfeghi
- Department of Mechanical Engineering, Sogang University, Seoul, South Korea
| | - H Motamedi
- Department of Mechanical Engineering, Tarbiat Modares University, Iran
| | - Y Sheikhnejad
- Centre for Mechanical Technology and Automation, Department of Mechanical Engineering, Universidade de Aveiro, 3810-193, Aveiro, Portugal
- PICadvanced SA, Creative Science Park, Via do Conhecimento, Ed. Central, 3830-352, Ílhavo, Portugal
| | - H Bordbar
- School of Engineering, Aalto University, Finland
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Motamedi H, Azizi A, Ahmadi M. Nutritive value of treated Quercus infectoria and Quercus libani leaves with the tannin-degrading bacterium Klebsiella pneumoniae for ruminant feeding in vitro. J Appl Microbiol 2019; 127:1339-1348. [PMID: 31386790 DOI: 10.1111/jam.14408] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2019] [Revised: 07/30/2019] [Accepted: 07/31/2019] [Indexed: 11/26/2022]
Abstract
AIMS This study was conducted to evaluate the chemical composition and in vitro gas production (GP) and fermentation parameters of Quercus infectoria and Quercus libani leaves following treatment with the Klebsiella pneumoniae, a tannin-degrading bacterium. METHODS AND RESULTS This isolate was isolated on medium containing tannic acid as the sole source of carbon and energy, and identified based on 16S rRNA sequencing analysis. In both oak leaf species (i.e. Q. infectoria and Q. libani), inoculation with Klebsiella pneumoniae significantly increased (P < 0·05) dry matter (DM) loss. For Q. libani, crude protein content was increased (P = 0·02) by bacterial treatment vs. control. In both oak leaves, total phenolic content and total tannins were decreased (P < 0·05) as a consequence of bacterial treatment. However, bacterial processing didn't changed (P > 0·05) organic matter (OM), neutral detergent fibre, acid detergent fibre or acid detergent lignin content of treated leaves. In both oak leaves the measuring parameters including GP volume, in vitro digestibility of DM and OM, estimated metabolizable energy, total volatile fatty acids, acetate, ammonia nitrogen concentration, total protozoal population and the subfamily Isotricha in treatments were higher (P < 0·05) than control. CONCLUSIONS It can be concluded that biological treatment of Q. infectoria and Q. libani leaves with K. pneumoniae represents a useful approach to decrease their phenolic compound content and improve their nutritive value as ruminant feed. SIGNIFICANCE AND IMPACT OF THE STUDY This study demonstrated that biologically processing of tannin-containing by-products with K. pneumoniae could increase their nutritive value as ruminant feeds and increase animal productivity.
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Affiliation(s)
- H Motamedi
- Department of Biology, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran.,Biotechnology and Biological Science Research Center, Shahid Chamran University of Ahvaz, Ahvaz, Iran
| | - A Azizi
- Department of Animal Science, Faculty of Agriculture, Lorestan University, Khorramabad, Iran
| | - M Ahmadi
- Department of Biology, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran
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Shakarami MH, Mohammadabadi T, Motamedi H, Sari M, Teimouri Yansari A. Isolation and identification of cellulolytic bacteria from gastrointestinal tract of Arabian horse and investigation of their effect on the nutritional value of wheat straw. J Appl Microbiol 2019; 127:344-353. [DOI: 10.1111/jam.14251] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Revised: 02/22/2019] [Accepted: 03/06/2019] [Indexed: 11/28/2022]
Affiliation(s)
- M. Harsini Shakarami
- Department of Animal Science Faculty of Animal Science and Food Technology Agricultural Sciences and Natural Resources University of Khuzestan Mollasani, Ahvaz Iran
| | - T. Mohammadabadi
- Department of Animal Science Faculty of Animal Science and Food Technology Agricultural Sciences and Natural Resources University of Khuzestan Mollasani, Ahvaz Iran
| | - H. Motamedi
- Department of Biology Faculty of Science Shahid Chamran University of Ahvaz Khuzestan Iran
- Biotechnology and Biological Science Research Center Shahid Chamran University of Ahvaz Khuzestan Iran
| | - M. Sari
- Department of Animal Science Faculty of Animal Science and Food Technology Agricultural Sciences and Natural Resources University of Khuzestan Mollasani, Ahvaz Iran
| | - A. Teimouri Yansari
- Department of Animal Science Faculty of Animal Science and Fisheries Sari Agricultural Sciences and Natural Resources University Sari Iran
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Darabpour E, Roayaei Ardakani M, Motamedi H, Ronagh MT, Najafzadeh H. Purification and optimization of production conditions of a marine-derived antibiotic and ultra-structural study on the effect of this antibiotic against MRSA. Eur Rev Med Pharmacol Sci 2012; 16:157-165. [PMID: 22428466] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
OBJECTIVES In this study we have attempted to partially purify, characterize and optimize the fermentation condition for the antimicrobial compound production with anti-MRSA (Methicillin Resistant Staphylococcus aureus) activity produced by Pseudoalteromonas piscicida PG-02 bacterium, isolated from the Persian Gulf, and finally understand the morphological changes in MRSA due to this antibiotic. MATERIALS AND METHODS Optimization process of antibacterial compound production was studied based on the sources of carbon and nitrogen, optimum temperature, optimum pH and optimum incubation time. The purification of intended antibiotic was done using TLC and also thermostability and enzymatic stability treatment was studied. Ultrastructural study on the effect of intended antibacterial compound on MRSA was done using a Transmission Electron Microscopy (TEM). RESULTS The optimized bioprocess conditions for the maximum production were at temperature 28 degrees C, pH 7, NaCI 0.5% (w/v), 96 hrs (incubation time), glucose and tryptone as carbon source and nitrogen source, respectively. The antibacterial component showed thermal sensitivity but it was sensitive to proteinase K, so this compound may have proteinaceous nature. The results of sonication revealed that this compound is accumulated in both intra- and extra-cellular locations. TEM pictures showed disorganization of cytoplasmic membrane upon the extract treatment comparing to control so, it can be said that this antibacterial compound can be considered as a bactericidal agent against MRSA. CONCLUSION On the basis of obtained results, this bacterium can be regarded as a valuable strain for discovery of new weapon as bactericidal agent in fighting against multi-drug resistant bacteria especially MRSA.
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Affiliation(s)
- E Darabpour
- Department of Biology, Faculty of Science, Shahid Chamran University, Ahvaz, Iran.
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Safary A, Ardakani MR, Suraki AA, Khiavi MA, Motamedi H. Isolation and Characterization of Biosurfactant Producing Bacteria from Caspian Sea. ACTA ACUST UNITED AC 2010. [DOI: 10.3923/biotech.2010.378.382] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Motamedi H, Darabpour E, Gholipour M, Nejad SS. Antibacterial Effect of Ethanolic and Methanolic Extracts of Plantago ovata
and Oliveria decumbens Endemic in Iran Against Some Pathogenic Bacteria. INT J PHARMACOL 2010. [DOI: 10.3923/ijp.2010.117.122] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Maleki S, Seyyednejad SM, Damabi NM, Motamedi H. Antibacterial activity of the fruits of Iranian Torilis leptophylla against some clinical pathogens. Pak J Biol Sci 2008; 11:1286-9. [PMID: 18819541 DOI: 10.3923/pjbs.2008.1286.1289] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The aim of this study was to examine the antimicrobial activity of the methanolic extract of Torilis leptophylla was tested on eleven bacteria (Bacillus anthracis, Bacillus subtilis, Bacillus pumilus, Staphylococcus aureus, Bacillus licheniformis, Brucella melitensis, Escherichia coli, Salmonella typhi, Proteus mirabilis, Bordetella bronshiseptica and Pseudomonas aeruginosa). Tested extract was effective against all bacteria but not B. subtilis. Consequently, the ethanolic extract had antibacterial activity on some pathogens thus confirming their use in folk medicine.
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Affiliation(s)
- S Maleki
- Department of Biology, School of Science, Shahid Chamran University, Ahwaz, Iran
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Seyyedneja S, Maleki S, Damab NM, Motamedi H. Antibacterial Activity of Prunus mahaleb and Parsley (Petroselinum crispum) Against Some Pathogen. ACTA ACUST UNITED AC 2007. [DOI: 10.3923/ajbs.2008.51.55] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Shafiee A, Harris G, Motamedi H, Rosenbach M, Chen T, Zink D, Heimbuch B. Microbial hydroxylation of rustmicin (galbonolide A) and galbonolide B, two antifungal products produced by Micromonospora sp. ACTA ACUST UNITED AC 2001. [DOI: 10.1016/s1381-1177(00)00067-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Biazzo DE, Motamedi H, Mark DF, Qureshi SA. A high-throughput assay to identify compounds that can induce dimerization of the erythropoietin receptor. Anal Biochem 2000; 278:39-45. [PMID: 10640351 DOI: 10.1006/abio.1999.4408] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Erythropoietin induces dimerization of the erythropoietin receptor on the surface of erythroid progenitor cells, promoting the differentiation of these cells into mature red blood cells. To facilitate screening of large chemical collections for identification of compounds that can dimerize erythropoietin receptor, we have developed a novel, high-throughput in vitro assay to detect compounds that can cause dimerization of the erythropoietin receptor in solution. To develop this assay, amino acid sequences corresponding to the extracellular domain of erythropoietin receptor were expressed in Escherichia coli as erythropoietin-binding protein (rEBP). A modified version of this protein ((33)P-rEBP) containing a protein kinase A substrate site incorporated into the rEBP was also expressed in E. coli and labeled in vitro using protein kinase A and ¿gamma-(33)PATP. An erythropoietin mimetic peptide (EMP-1), that induces dimerization of rEBP in solution was used to demonstrate dimerization of (33)P-rEBP and rEBP in a 96-well microtiter plate format. EMP-1 induced dimerization of rEBP in this assay with an EC(50) of approximately 245 nM and had a maximal effect at 0.5-2 microM and required the presence of rEBP immobilized on the plate capable of binding EMP-1. EMP-1-induced dimerization of (33)P-rEBP and rEBP was reversed by excess unlabeled rEBP and was not masked by complex mixtures such as whole cell fungal extracts. These data demonstrate the ability of (33)P-rEBP to dimerize with rEBP in vitro in a format that is fully compatible with high-throughput screening.
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Affiliation(s)
- D E Biazzo
- Merck Research Laboratories, Rahway, New Jersey 07065-0900, USA
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Qureshi SA, Kim RM, Konteatis Z, Biazzo DE, Motamedi H, Rodrigues R, Boice JA, Calaycay JR, Bednarek MA, Griffin P, Gao YD, Chapman K, Mark DF. Mimicry of erythropoietin by a nonpeptide molecule. Proc Natl Acad Sci U S A 1999; 96:12156-61. [PMID: 10518592 PMCID: PMC18428 DOI: 10.1073/pnas.96.21.12156] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Erythropoietin (EPO) controls the proliferation and differentiation of erythroid progenitor cells into red blood cells. EPO induces these effects by dimerization of the EPO receptors (EPOR) present on these cells. To discover nonpeptide molecules capable of mimicking the effects of EPO, we identified a small molecule capable of binding to one chain of EPOR and used it to synthesize molecules capable of inducing dimerization of the EPOR. We first identified compound 1 (N-3-[2-(4-biphenyl)-6-chloro-5-methyl]indolyl-acetyl-L-lysine methyl ester) by screening the in-house chemical collection for inhibitors of EPO binding to human EPOR and then prepared compound 5, which contains eight copies of compound 1 held together by a central core. Although both compounds inhibited EPO binding of EPOR, only compound 5 induced dimerization of soluble EPOR. Binding of EPO to its receptor in cells results in activation of many intracellular signaling molecules, including transcription factors like signal transducer and activator of transcription (STAT) proteins, leading to growth and differentiation of these cells. Consistent with its ability to induce dimerization of EPOR in solution, compound 5 exhibited much of the same biological activities as EPO, such as (i) the activation of a STAT-dependent luciferase reporter gene in BAF3 cells expressing human EPOR, (ii) supporting the proliferation of several tumor cell lines expressing the human or mouse EPOR, and (iii) the in vitro differentiation of human progenitor cells into colonies of erythrocytic lineage. These data demonstrate that a nonpeptide molecule is capable of inducing EPOR dimerization and mimicking the biological activities of EPO.
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Affiliation(s)
- S A Qureshi
- Merck Research Laboratories, Rahway, NJ 07065, USA.
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Abstract
Biosynthesis of the macrolactone ring of FK506 involves 10 elongation cycles that mechanistically resemble the steps in fatty acid synthesis. Sequencing of a 40-kb DNA segment of the FK506 gene cluster from Streptomyces sp. MA6548 has revealed two additional polyketide synthases (PKS) genes fkbB and fkbC which lie upstream of fkbA, a PKS gene recently shown to be responsible for the last four condensation steps of the FK506 biosynthesis [Motamedi, H., Cai, S. J., Shafiee, A. & Elliston, K. O. (1997) Eur. J. Biochem. 244, 74-80]. fkbB and fkbC are contiguous and encode respectively, the first (790129 Da) and the second (374438 Da) components of the FK506 polyketide synthase, a complex of three multidomain polypeptides. The predicted domain structures of FkbB and FkbC are analogous to that of FkbA and comprise 30 fatty-acid-synthase(FAS)-like domains arranged in 6 modules. Each module performs a specific extension cycle in the assembly of the carbon skeleton of the FK506 macrolactone ring. The component activities for the initiation of the polyketide chain consisting of a dihydrocyclohexenylcarbonyl coenzyme A (CoA) synthetase and a dihydrocyclohexenylcarbonyl CoA reductase required for the formation of the dihydrocyclohexylcarbonyl CoA starter unit and an acyl-carrier-protein to which the starter unit is anchored and translocated to the appropriate site on the PKS multienzyme are located at the N-terminal region of the FkbB polypeptide. A third gene, fkbL, lies at one end of the cluster and encodes lysine cyclodeaminase which catalyzes alpha-deamination and cyclization of the lysine into pipecolate. A fourth gene fkbP located at the other end of the sequence reported here encodes a peptide synthetase required for the activation and incorporation of the pipecolate moiety into the completed acyl chain. Finally the cluster carries a gene, fkbO, whose product is presumed to carry out a post-polyketide oxidation step of the FK506 marocycle.
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Affiliation(s)
- H Motamedi
- Department of Molecular Pharmacology and Biochemistry, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
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Shafiee A, Motamedi H, King A. Purification, characterization and immobilization of an NADPH-dependent enzyme involved in the chiral specific reduction of the keto ester M, an intermediate in the synthesis of an anti-asthma drug, Montelukast, from Microbacterium campoquemadoensis (MB5614). Appl Microbiol Biotechnol 1998. [DOI: 10.1007/s002530051236] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Shafiee A, Motamedi H, Dumont FJ, Arison BH, Miller RR. Chemical and biological characterization of two FK506 analogs produced by targeted gene disruption in Streptomyces sp. MA6548. J Antibiot (Tokyo) 1997; 50:418-23. [PMID: 9207912 DOI: 10.7164/antibiotics.50.418] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Two genetically engineered mutant strains of Streptomyces sp. MA6548 produced two FK506 analogs, 9-deoxo-31-O-demethylFK506 and 31-O-demethylFK506. The structures were determined by a combination of NMR and mass spectrometry. These compounds exhibited immunosuppressive and antifungal activities, albeit reduced, compared to FK506. Both compounds contain a free hydroxyl group at C-31 for the synthesis of novel FK506 derivatives.
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Affiliation(s)
- A Shafiee
- Department of Natural Products Drug Discovery, Merck Research Laboratories, Rahway, New Jersey 07065, USA
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Motamedi H, Cai SJ, Shafiee A, Elliston KO. Structural organization of a multifunctional polyketide synthase involved in the biosynthesis of the macrolide immunosuppressant FK506. Eur J Biochem 1997; 244:74-80. [PMID: 9063448 DOI: 10.1111/j.1432-1033.1997.00074.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The immunosuppressant FK506 is a 23-membered macrocyclic polyketide produced by several Streptomyces species. Sequencing of a 19.5-kb contiguous segment of DNA from the FK506 gene cluster of Streptomyces sp. MA6548 revealed the presence of a single 19.3-kb open reading frame designated fkbA. fkbA encodes a component of the FK506 polyketide synthase, a complex enzyme system which catalyzes synthesis of the polyketide portion of FK506. The predicted product of gene fkbA is a 630,660-Da protein (6420 amino acids) that contains 19 independent domains with a high degree of amino acid sequence similarity to the catalytic activities of known fatty acid synthases. The identified domains are arranged into four repeated modules with a linear organization precisely as that of animal fatty acid synthase and type I polyketide synthase. Each module participates in one round of chain extension and subsequent processing and thus FkbA polypeptide catalyzes four of the ten condensation steps required for synthesis of the FK506 macrolactone ring. Disruption of fkbA results in the generation of an FK506 non-producing mutant demonstrating direct involvement of fkbA in the biosynthesis of FK506.
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Affiliation(s)
- H Motamedi
- Dept. of Natural Products Drug Discovery, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
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Motamedi H, Shafiee A, Cai SJ, Streicher SL, Arison BH, Miller RR. Characterization of methyltransferase and hydroxylase genes involved in the biosynthesis of the immunosuppressants FK506 and FK520. J Bacteriol 1996; 178:5243-8. [PMID: 8752344 PMCID: PMC178323 DOI: 10.1128/jb.178.17.5243-5248.1996] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
FK506 and FK520 are 23-membered macrocyclic polyketides with potent immunosuppressive and antifungal activities. The gene encoding 31-O-demethyl-FK506 methyltransferase, fkbM, was isolated from Streptomyces sp. strains MA6858 and MA6548, two FK506 producers, and Streptomyces hygroscopicus subsp. ascomyceticus, an FK520 producer. The nucleotide sequence of the fkbM gene revealed an open reading frame encoding a polypeptide of 260 amino acids. Disruption of fkbM in Streptomyces sp. strain MA6548 yielded a mutant that produced 31-O-demethyl-FK506, confirming the involvement of the isolated genes in the biosynthesis of FK506 and FK520. Heterologous expression of fkbM in Streptomyces lividans established that fkbM encodes an O-methyltransferase catalyzing the methylation of the C-31 hydroxyl group of 31-O-demethyl-FK506 and FK520. A second open reading frame, fkbD, was found upstream of fkbM in all three aforementioned species and was predicted to encode a protein of 388 residues that showed a strong resemblance to cytochrome P-450 hydroxylases. Disruption of fkbD had a polar effect on the synthesis of the downstream fkbM gene product and resulted in the formation of 9-deoxo-31-O-demethyl-FK506. This established the product of fkbD as the cytochrome P-450 9-deoxo-FK506 hydroxylase, which is responsible for hydroxylation at position C-9 of the FK506 and FK520 macrolactone ring.
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Affiliation(s)
- H Motamedi
- Department of Natural Products Drug Discovery, Merck Research Laboratories, Rahway, New Jersey 07065, USA
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Decker H, Rohr J, Motamedi H, Zähner H, Hutchinson CR. Identification of Streptomyces olivaceus Tü 2353 genes involved in the production of the polyketide elloramycin. Gene 1995; 166:121-6. [PMID: 8529875 DOI: 10.1016/0378-1119(95)00573-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The genes for the production of elloramycin (ELM) from Streptomyces olivaceus (So) Tü2353 were cloned using a polyketide synthase gene probe from the tetracenomycin pathway. A cosmid clone (16F4) isolated from a gene library of So Tü2353 conferred tetracenomycin C and ELM resistance to S. lividans TK64 and complemented a mutation in So Tü2353R. Introduction of cosmid 16F4 into S. lividans TK64 resulted in the production of 8-demethyl-tetracenomycin C, an intermediate of ELM biosynthesis.
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Affiliation(s)
- H Decker
- Biologisches Institut, Universität Tübingen, Germany
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Abstract
Integrative expression vectors for heterologous expression of the genes in Streptomyces were developed. The vectors are comprised of a strong constitutive promoter, PE, a synthetic ribosome-binding site, ATG start codon, multiple cloning site, transcription terminator and hygromycin-resistance-encoding gene. The vectors also contain a ColE1 replicon for propagation in Escherichia coli and a wide-host-range Streptomyces integration element, the mini-circle, to direct the insertion of the vectors into the Streptomyces genome at the mini-circle attachment site. HyR transformants are stable in the absence of drug selection. Conjugative derivatives were also constructed by incorporating oriT, the origin of transfer of the IncP plasmid RK2, into these vectors, and conjugal transfer was demonstrated from an appropriate E. coli donor to Steptomyces lividans (Sl). Derivatives of these vectors potentially useful for gene disruption, as well as complementation, are also described. Replicative forms of the constructed mini-circle-based vectors in Sl, that co-exist with the integrated copy of the vector, were also present without any apparent instability problems. The utility of the vectors was demonstrated by expression of the gene encoding 31-O-methyltransferase, which is involved in methylation at position 31 of the immunosuppressive drug FK506, in Sl.
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Affiliation(s)
- H Motamedi
- Merck Research Laboratories, Rahway, NJ 07065, USA
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Shafiee A, Motamedi H, Chen T. Enzymology of FK-506 biosynthesis. Purification and characterization of 31-O-desmethylFK-506 O:methyltransferase from Streptomyces sp. MA6858. Eur J Biochem 1994; 225:755-64. [PMID: 7525282 DOI: 10.1111/j.1432-1033.1994.00755.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
FK-506 is a macrolide antibiotic with immunosuppressant activity. Structurally, this compound contains three methylated hydroxyl groups at C13, C15 and C31. Previous biosynthetic studies using stable isotope-feeding experiments have established methionine as the source of the methyl for these methylated hydroxyl groups. Based on this information and also the availability of the 31-O-desmethylFK-506, a metabolic precursor for the biosynthesis of FK-506, a S-adenosyl-L-methionine-dependent enzyme assay was developed and the enzyme 31-O-desmethylFK-506 O:methyl-transferase was isolated from an extract of Streptomyces sp. MA 6858 and purified to near homogeneity. 31-O-DesmethylFK-506 O:methyltransferase is a monomeric protein with an apparent molecular mass of 30,000 Da and a pI of 4.4. The first 38 N-terminal amino acids have been sequenced and are H2N-SDVVETLRLPNGATVAHVNAGEAQFLYREIFTDRXYLRH. Functionally, This enzyme has a requirement for Mg2+ with an optimum temperature of 34 degrees C and a pH of 7.4 for full activity. Moreover, it catalyses the methylation of 31-O-desmethylimmunomycin as efficiently as its own natural substrate, 31-O-desmethylFK-506. Additionally, FKMT catalyzes the C31 transmethylation reaction of 13,31-O-bis-desmethyl-, 15,31-O-bisdesmethyl-, 13,15,31-O-trisdesmethyl- and 31-O-19,22-cyclic-hemiketalimmunomycins, which are all structural analogues of FK-506. The reaction is, however, completely blocked if the vicinal hydroxyl which is present at the C-32 position of the 31-O-desmethylFK-506 structure is replaced with azide, phosphate or other substituents. Finally, evidence is presented indicating the close similarity of FKMT and DIMT, a 31-O-desmethyl-immunomycin: O methyltransferase, previously isolated from a cell-free extract of Streptomyces hygroscopicus var ascomyceticus, an immunomycin (ascomycin/FK-520) producer.
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Affiliation(s)
- A Shafiee
- Department of Microbial Therapeutics and Molecular Genetics, Merck Research Laboratories, Rahway, NJ 07065
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Summers RG, Wendt-Pienkowski E, Motamedi H, Hutchinson CR. The tcmVI region of the tetracenomycin C biosynthetic gene cluster of Streptomyces glaucescens encodes the tetracenomycin F1 monooxygenase, tetracenomycin F2 cyclase, and, most likely, a second cyclase. J Bacteriol 1993; 175:7571-80. [PMID: 8244926 PMCID: PMC206913 DOI: 10.1128/jb.175.23.7571-7580.1993] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Certain mutations in the tcmVI region of the Streptomyces glaucescens chromosome affect formation of the D ring of the polyketide antibiotic tetracenomycin C (TCM C). This region lies immediately upstream from the TCM C polyketide synthase genes (tcmKLM), and the nucleotide sequence reveals the presence of three small genes, tcmH, tcmI, and tcmJ. On the basis of the phenotypes of mutants and the effects of these genes, when coupled on a plasmid with the tcmKLMN177 genes (tcmN177 is a 3'-truncated version of tcmN), on the production of TCM intermediates in a TCM- mutant, the tcmH gene encodes the C-5 monooxygenase that converts TCM F1 to TCM D3, the tcmI gene encodes the D-ring cyclase that converts TCM F2 to TCM F1 (mutations in this gene are responsible for the type VI phenotype), and the tcmJ gene most likely encodes the B-ring cyclase that acts in the biosynthesis of TCM F2. Furthermore, it appears that the N-terminal domain of the tcmN gene product (encoded by the tcmN177 gene) acts later in the biosynthesis of TCM F2 than the product of tcmJ, suggesting that the N-terminal domain of the TcmN protein is the C-ring cyclase.
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Affiliation(s)
- R G Summers
- School of Pharmacy, University of Wisconsin-Madison 53706
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Decker H, Motamedi H, Hutchinson CR. Nucleotide sequences and heterologous expression of tcmG and tcmP, biosynthetic genes for tetracenomycin C in Streptomyces glaucescens. J Bacteriol 1993; 175:3876-86. [PMID: 8509339 PMCID: PMC204804 DOI: 10.1128/jb.175.12.3876-3886.1993] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The nucleotide sequence of the tcmIII, tcmIc, and tcmVII region of the tetracenomycin (TCM) C gene cluster of Streptomyces glaucescens ETH 22794 (GLA.0) revealed the presence of two genes, tcmP and tcmG. The deduced product of tcmG resembles flavoprotein hydroxylases found in several other bacteria, whereas the predicted amino acid sequence of tcmP is not significantly similar to those of any known proteins in the available data bases. Southern blot hybridization revealed an approximately 180-bp deletion in a tcmIII (tcmG) mutant and a 1,800-bp insertion in a tcmVII (tcmP) mutant. Heterologous expression of tcmG and tcmP in Streptomyces lividans and tcmP in Escherichia coli established that tcmP encodes an O-methyltransferase, catalyzing the methylation of the C-9 carboxy group of TCM E to yield TCM A2, and that tcmG is responsible for the hydroxylation of TCM A2 at positions C-4, C-4a, and C-12a to give TCM C. These are the final two steps of TCM C biosynthesis.
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Affiliation(s)
- H Decker
- School of Pharmacy, University of Wisconsin, Madison 53706
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Garrity GM, Heimbuch BK, Motamedi H, Shafiee A. Genetic relationships among actinomycetes that produce the immunosuppressant macrolides FK506, FK520/FK523 and rapamycin. J Ind Microbiol 1993; 12:42-7. [PMID: 7688970 DOI: 10.1007/bf01570127] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A polyphasic taxonomic study was undertaken to establish the genetic and phenotypic relationships among six actinomycetes that produce the immunosuppressant macrolides FK506, FK520/FK523 and rapamycin. Chemotaxonomic studies reveal that all have Type I cell walls. Gas chromatography (GC) of fatty acid methyl esters revealed patterns consistent for strains of Streptomyces with 16:0 and 15:0 anteiso predominating. Principal component analysis of GC data revealed distinct profiles for each culture. Reciprocal DNA homology studies at Tm-25 showed the rapamycin-producing strain and one FK506-producing strain to have 38-50% homology with the type strain of Streptomyces hygroscopicus (ATCC 27438). The remaining strains exhibited 6-17% homology. To further explore the relationships among these strains all were probed for the presence of an O-methyltransferase gene specific to this biosynthetic pathway. Among the strains of interest, only Streptomyces hygroscopicus subsp. yakushimaensis, the patent strain for FK520/FK523, failed to hybridize with the probes.
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Affiliation(s)
- G M Garrity
- Basic Microbiology Department, Merck Research Laboratories, Merck & Co., Rahway, NJ 07065
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Summers RG, Wendt-Pienkowski E, Motamedi H, Hutchinson CR. Nucleotide sequence of the tcmII-tcmIV region of the tetracenomycin C biosynthetic gene cluster of Streptomyces glaucescens and evidence that the tcmN gene encodes a multifunctional cyclase-dehydratase-O-methyl transferase. J Bacteriol 1992; 174:1810-20. [PMID: 1548230 PMCID: PMC205782 DOI: 10.1128/jb.174.6.1810-1820.1992] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Mutations in the tcmII-tcmIV region of the Streptomyces glaucescens chromosome block the C-3 and C-8 O-methylations of the polyketide antibiotic tetracenomycin C (Tcm C). The nucleotide sequence of this region reveals the presence of two genes, tcmN and tcmO, whose deduced protein products display similarity to the hydroxyindole O-methyl transferase of the bovine pineal gland, an enzyme that catalyzes a phenolic O-methylation analogous to those required for the biosynthesis of Tcm C. The deduced product of the tcmN gene also has an N-terminal domain that shows similarity to the putative ActVII and WhiE ORFVI proteins of Streptomyces coelicolor. The tcmN N-terminal domain can be separated from the remainder of the tcmN gene product, and when coupled on a plasmid with the Tcm C polyketide synthase genes (tcmKLM), this domain enables high-level production of an early, partially cyclized intermediate of Tcm C in a Tcm C- null mutant or in a heterologous host (Streptomyces lividans). By analogy to fatty acid biosynthesis, the tcmKLM polyketide synthase gene products are probably sufficient to produce the linear decaketide precursor of Tcm C; thus, the tcmN N-terminal domain is most likely responsible for one or more of the early cyclizations and, perhaps, the attendant dehydrations that lead to the partially cyclized intermediate. The tcmN gene therefore appears to encode a multifunctional cyclase-dehydratase-3-O-methyl transferase. The tcmO gene encodes the 8-O-methyl transferase.
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Affiliation(s)
- R G Summers
- School of Pharmacy, University of Wisconsin-Madison 53706
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Hutchinson CR, Borell CW, Donovan MJ, Kato F, Motamedi H, Nakayama H, Otten SL, Rubin RL, Streicher SL, Stutzman-Engwall KJ. Drug development through the genetic engineering of antibiotic-producing microorganisms. Ann N Y Acad Sci 1991; 646:78-93. [PMID: 1809208 DOI: 10.1111/j.1749-6632.1991.tb18566.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- C R Hutchinson
- School of Pharmacy, Department of Bacteriology, University of Wisconsin, Madison 53706
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Hutchinson CR, Borell CW, Donovan MJ, Kato F, Motamedi H, Nakayama H, Rubin RL, Streicher SL, Summers RG, Wendt-Pienkowski E, Wessel WL. The genetic and biochemical basis of polyketide metabolism in microorganisms and its role in drug discovery and development. Planta Med 1991; 57:S36-43. [PMID: 17226221 DOI: 10.1055/s-2006-960227] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The possibilities for the design of new drug screening and development strategies directed to a specific objective on the basis of genetic engineering of microorganisms is discussed from two points of view. Firstly, results of work on genetic hybrids of STREPTOMYCES species for the production of new metabolites such as mederrhodin (1) and aloespanoarin II (4) are described. Secondly, the enhanced production of known metabolites such as tetracenomycin A (2) (11) and tetracenomycin C (9) by recombinant STREPTOMYCES species is considered. Mechanistic aspects of polyketide metabolism are included.
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Affiliation(s)
- C R Hutchinson
- School of Pharmacy and Department of Bacteriology, University of Wisconsin, 425 N Charter St., Madison, Wisconsin 53706, U.S.A
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Bibb MJ, Biró S, Motamedi H, Collins JF, Hutchinson CR. Analysis of the nucleotide sequence of the Streptomyces glaucescens tcmI genes provides key information about the enzymology of polyketide antibiotic biosynthesis. EMBO J 1989; 8:2727-36. [PMID: 2684656 PMCID: PMC401280 DOI: 10.1002/j.1460-2075.1989.tb08414.x] [Citation(s) in RCA: 215] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Key information about the biosynthesis of polyketide metabolites has been uncovered by sequence analysis of the tetracenomycin C polyketide synthase genes (tcml) from Streptomyces glaucescens GLA.0. The sequence data revealed the presence of three complete open reading frames (ORFs). ORF1 and ORF2 appear to be translationally coupled and would encode proteins containing 426 and 405 amino acids, respectively. The two deduced proteins are homologous to known beta-ketoacyl synthases. ORF3 begins 70 nucleotides after the stop codon of ORF2 and would code for an 83 amino acid protein with a strong resemblance to known bacterial, animal and plant acyl-carrier proteins (ACP). The presence of an ACP gene within the tcm gene cluster suggests that different ACPs are used in fatty acid and polyketide biosynthesis in Streptomyces. We conclude from these data and earlier information that polyketide biosynthesis in S. glaucescens, and most likely in other bacteria, involves a multienzyme complex consisting of at least five types of enzymes: acylCoA transferases that load the acyl and 2-carboxyacyl precursors onto the ACP; a beta-ketoacyl synthase that, along with the acylated ACP, forms the poly-beta-ketoacyl intermediates; a poly-beta-ketone cyclase that forms carbocyclic structures from the latter intermediates; a beta-ketoacyl oxidoreductase that forms beta-hydroxyacyl intermediates or reduces ketone groups in fully formed polyketides; and a thioesterase that releases the assembled polyketide from the enzyme.
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Affiliation(s)
- M J Bibb
- John Innes Institute, Norwich, UK
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Motamedi H, Hutchinson CR. Cloning and heterologous expression of a gene cluster for the biosynthesis of tetracenomycin C, the anthracycline antitumor antibiotic of Streptomyces glaucescens. Proc Natl Acad Sci U S A 1987; 84:4445-9. [PMID: 3474613 PMCID: PMC305106 DOI: 10.1073/pnas.84.13.4445] [Citation(s) in RCA: 92] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Through complementation of mutations specifically blocking the biosynthesis of tetracenomycin C by Streptomyces glaucescens and selecting for resistance to tetracenomycin C in Streptomyces lividans, all of the genes for the production of tetracenomycin C were inserted in pIJ702, a high copy-number Streptomyces gene cloning vector. The tcm biosynthetic and resistance genes occur as a single cluster in the S. glaucescens genome and are expressed in heterologous streptomycete hosts like S. lividans, resulting in the overproduction of pigmented intermediates of the tetracenomycin C biosynthetic pathway.
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Malpartida F, Hallam SE, Kieser HM, Motamedi H, Hutchinson CR, Butler MJ, Sugden DA, Warren M, McKillop C, Bailey CR. Homology between Streptomyces genes coding for synthesis of different polyketides used to clone antibiotic biosynthetic genes. Nature 1987; 325:818-21. [PMID: 3029594 DOI: 10.1038/325818a0] [Citation(s) in RCA: 128] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Many important antibiotics such as tetracyclines, erythromycin, adriamycin, monensin, rifamycin and avermectins are polyketides. In their biosynthesis, multifunctional synthases catalyse iterated condensation of thio-esters derived from acetate, propionate or butyrate to yield aliphatic chains of varying length and carrying different alkyl substituents. Subsequent modifications, including aromatic or macrolide ring closure or specific methylations or glycosylations, generate further chemical diversity. It has been suggested that, if different polyketide synthases had a common evolutionary origin, cloned DNA coding for one synthase might be used as a hybridization probe for the isolation of others. We show here that this is indeed possible. Study of a range of such synthase genes and their products should help to elucidate what determines the choice and order of condensation of different residues in polyketide assembly, and might yield, by in vitro recombination or mutagenesis, synthase genes capable of producing novel antibiotics. Moreover, because genes for entire antibiotic pathways are usually clustered in Streptomyces, cloned polyketide synthase genes are valuable in giving access to groups of linked biosynthetic genes.
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Abstract
We analyzed the properties of tetracenomycin C (TcmC)-nonproducing mutants of Streptomyces glaucescens to establish the nature of pathway intermediates and to provide some information about the genetics of antitumor anthracycline antibiotic production. Using cosynthesis properties and metabolite accumulation data, we classified a collection of 34 TcmC-nonproducing strains into seven different groups. From this information, we deduced the positions of the tcm mutations in relation to a hypothetical TcmC biosynthetic pathway and suggest which pathway enzymes are affected by the different mutations.
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Yue S, Motamedi H, Wendt-Pienkowski E, Hutchinson CR. Anthracycline metabolites of tetracenomycin C-nonproducing Streptomyces glaucescens mutants. J Bacteriol 1986; 167:581-6. [PMID: 3460987 PMCID: PMC212929 DOI: 10.1128/jb.167.2.581-586.1986] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Mutants of Streptomyces glaucescens GLA.0 which are blocked in the production of tetracenomycin C (compound 1), an anthracycline antibiotic having significant antitumor activity, accumulated several new anthracycline metabolites structurally related to compound 1 and to intermediates of its biosynthetic pathway. Through chemical and spectroscopic comparisons with the known anthracycline metabolites of the wild-type strain, we identified the two regioisomers of tetracenomycin B2 (compounds 7a and 7b), 8-demethyltetracenomycin C (compound 12), tetracenomycin D2 (compound 11), tetracenomycin E (compound 13), and the 12-naphthacenone forms of compounds 7a, 7b, and 2 (tetracenomycin D1). A hypothetical biosynthetic pathway to compound 1 is presented that is consistent with the occurrence of compounds 7b, 13, and 5 (tetracenomycin A2) and with the cosynthetic behavior of tetracenomycin C-nonproducing mutants (H. Motamedi, E. Wendt-Pienkowski, and C. R. Hutchinson, J. Bacteriol. 167:575-580, 1986).
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Motamedi H, Lee Y, Schmidt FJ. Tandem promoters preceding the gene for the M1 RNA component of Escherichia coli ribonuclease P. Proc Natl Acad Sci U S A 1984; 81:3959-63. [PMID: 6204333 PMCID: PMC345347 DOI: 10.1073/pnas.81.13.3959] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The nucleotide sequence of a cloned gene for the RNA component of Escherichia coli ribonuclease P, M1 RNA, is presented. The sequence determined extends 320 nucleotides upstream of the 377-base-pair (bp) structural gene and includes three sequences homologous to the consensus E. coli promoter sequence. Two nucleotides found in the M1 RNA structural gene sequence were not found in a previously determined gene sequence of another M1 RNA clone [Reed, R. E., Baer, M. F., Guerrier-Takeda, C., Donis-Keller, H. & Altman, S. (1982) Cell 30, 627-636]. In vitro transcription of supercoiled plasmid DNA containing the M1 RNA gene resulted in a major transcript arising from the strong promoter nearest to the mature M1 RNA. RNAs encoded by the M1 RNA clone in vivo were examined by S1 nuclease mapping. The results indicated that in vivo transcripts originate from all three promoters preceding the M1 RNA gene. These transcripts are apparently processed in a multistep pathway to generate the 5' end of mature M1 RNA.
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Motamedi H, Lee K, Nichols L, Schmidt FJ. An RNA species involved in Escherichia coli ribonuclease P activity. Gene cloning and effect on transfer RnA synthesis in vivo. J Mol Biol 1982; 162:535-50. [PMID: 6187925 DOI: 10.1016/0022-2836(82)90387-4] [Citation(s) in RCA: 39] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Kamyab S, Baghdiantz A, Motamedi H. Variations in serum protein fractions following a continuous long term intake of eugynon and lyndiol by Iranian women. J Steroid Biochem 1978; 9:811-2. [PMID: 713559 DOI: 10.1016/0022-4731(78)90205-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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