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Gazit VA, Swietlicki EA, Liang MU, Surti A, McDaniel R, Geisman M, Alvarado DM, Ciorba MA, Bochicchio G, Ilahi O, Kirby J, Symons WJ, Davidson NO, Levin MS, Rubin DC. Stem cell and niche regulation in human short bowel syndrome. JCI Insight 2020; 5:137905. [PMID: 33141758 PMCID: PMC7714413 DOI: 10.1172/jci.insight.137905] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Accepted: 10/28/2020] [Indexed: 12/20/2022] Open
Abstract
Loss of functional small bowel surface area following surgical resection for disorders such as Crohn’s disease, intestinal ischemic injury, radiation enteritis, and in children, necrotizing enterocolitis, atresia, and gastroschisis, may result in short bowel syndrome, with attendant high morbidity, mortality, and health care costs in the United States. Following resection, the remaining small bowel epithelium mounts an adaptive response, resulting in increased crypt cell proliferation, increased villus height, increased crypt depth, and enhanced nutrient and electrolyte absorption. Although these morphologic and functional changes are well described in animal models, the adaptive response in humans is less well understood. Clinically the response is unpredictable and often inadequate. Here we address the hypotheses that human intestinal stem cell populations are expanded and that the stem cell niche is regulated following massive gut resection in short bowel syndrome (SBS). We use intestinal enteroid cultures from patients with SBS to show that the magnitude and phenotype of the adaptive stem cell response are both regulated by stromal niche cells, including intestinal subepithelial myofibroblasts, which are activated by intestinal resection to enhance epithelial stem and proliferative cell responses. Our data suggest that myofibroblast regulation of bone morphogenetic protein signaling pathways plays a role in the gut adaptive response after resection. LGR5+ stem cells are expanded and BMP signaling regulates the stem cell niche in human short bowel syndrome.
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Affiliation(s)
- Vered A Gazit
- Division of Gastroenterology, John T. Milliken Department of Medicine
| | | | - Miranda U Liang
- Division of Gastroenterology, John T. Milliken Department of Medicine
| | - Adam Surti
- Division of Gastroenterology, John T. Milliken Department of Medicine
| | - Raechel McDaniel
- Division of Gastroenterology, John T. Milliken Department of Medicine
| | - Mackenzie Geisman
- Division of Gastroenterology, John T. Milliken Department of Medicine
| | - David M Alvarado
- Division of Gastroenterology, John T. Milliken Department of Medicine
| | - Matthew A Ciorba
- Division of Gastroenterology, John T. Milliken Department of Medicine
| | | | | | | | | | - Nicholas O Davidson
- Division of Gastroenterology, John T. Milliken Department of Medicine.,Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Marc S Levin
- Division of Gastroenterology, John T. Milliken Department of Medicine.,Veterans Affairs Medical Center, St. Louis, Missouri, USA
| | - Deborah C Rubin
- Division of Gastroenterology, John T. Milliken Department of Medicine.,Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri, USA
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Cracknell L, Rodriguez L, McDaniel R, Xiangshan Z, Turner E, Annesi C, Chaozhong Z. PO-283 Characterisation of hTERT-immortalised prostate-derived stromal and epithelial cells: an authentic in vitro model for tumour microenvironment studies. ESMO Open 2018. [DOI: 10.1136/esmoopen-2018-eacr25.797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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3
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Lopez-Soberal L, Wenzel C, McDaniel R, Dodd H, Bowser J, Swiderski C. Precision-cut lung slicing: A tool for investigating airway hyper-responsiveness in horses. J Equine Vet Sci 2017. [DOI: 10.1016/j.jevs.2017.03.065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Pusterla N, Kass PH, Mapes S, Johnson C, Barnett DC, Vaala W, Gutierrez C, McDaniel R, Whitehead B, Manning J. Surveillance programme for important equine infectious respiratory pathogens in the USA. Vet Rec 2011; 169:12. [PMID: 21676986 DOI: 10.1136/vr.d2157] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The prevalence and epidemiology of important viral (equine influenza virus [EIV], equine herpesvirus type 1 [EHV-1] and EHV-4) and bacterial (Streptococcus equi subspecies equi) respiratory pathogens shed by horses presented to equine veterinarians with upper respiratory tract signs and/or acute febrile neurological disease were studied. Veterinarians from throughout the USA were enrolled in a surveillance programme and were asked to collect blood and nasal secretions from equine cases with acute infectious upper respiratory tract disease and/or acute onset of neurological disease. A questionnaire was used to collect information pertaining to each case and its clinical signs. Samples were tested by real-time PCR for the presence of EHV-1, EHV-4, EIV and S equi subspecies equi. A total of 761 horses, mules and donkeys were enrolled in the surveillance programme over a 24-month study period. In total, 201 (26.4 per cent) index cases tested PCR-positive for one or more of the four pathogens. The highest detection rate was for EHV-4 (82 cases), followed by EIV (60 cases), S equi subspecies equi (49 cases) and EHV-1 (23 cases). There were 15 horses with double infections and one horse with a triple infection. The detection rate by PCR for the different pathogens varied with season and with the age, breed, sex and use of the animal.
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Affiliation(s)
- N Pusterla
- Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
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Hu Z, Desai RP, Volchegursky Y, Leaf T, Woo E, Licari P, Santi DV, Hutchinson CR, McDaniel R. Approaches to stabilization of inter-domain recombination in polyketide synthase gene expression plasmids. J Ind Microbiol Biotechnol 2003; 30:161-7. [PMID: 12715253 DOI: 10.1007/s10295-003-0029-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2002] [Accepted: 12/21/2002] [Indexed: 11/25/2022]
Abstract
Regions of extremely high sequence identity are recurrent in modular polyketide synthase (PKS) genes. Such sequences are potentially detrimental to the stability of PKS expression plasmids used in the combinatorial biosynthesis of polyketide metabolites. We present two different solutions for circumventing intra-plasmid recombination within the megalomicin PKS genes in Streptomyces coelicolor. In one example, a synthetic gene was used in which the codon usage was reengineered without affecting the primary amino acid sequence. The other approach utilized a heterologous subunit complementation strategy to replace one of the problematic regions. Both methods resulted in PKS complexes capable of 6-deoxyerythronolide B analogue biosynthesis in S. coelicolor CH999, permitting reproducible scale-up to at least 5-l stirred-tank fermentation and a comparison of diketide precursor incorporation efficiencies between the erythromycin and megalomicin PKSs.
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Affiliation(s)
- Z Hu
- Kosan Biosciences Inc., 3832 Bay Center Place, Hayward, CA 94545, USA
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6
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McDaniel R, Licari P, Khosla C. Process development and metabolic engineering for the overproduction of natural and unnatural polyketides. Adv Biochem Eng Biotechnol 2002; 73:31-52. [PMID: 11816811 DOI: 10.1007/3-540-45300-8_3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
Polyketide natural products are a rich source of bioactive substances that have found considerable use in human health and agriculture. Their complex structures require that they be produced via fermentation processes. This review describes the strategies and challenges used to develop practical fermentation strains and processes for polyketide production. Classical strain improvement procedures, process development methods, and metabolic engineering approaches are described. The elucidation of molecular mechanisms that underlie polyketide biosynthesis has played an important role in each of these areas over the past few years.
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Affiliation(s)
- R McDaniel
- KOSAN Biosciences, Inc., 3832 Bay Center Place, Hayward, CA 94545, USA
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Reeves CD, Murli S, Ashley GW, Piagentini M, Hutchinson CR, McDaniel R. Alteration of the substrate specificity of a modular polyketide synthase acyltransferase domain through site-specific mutations. Biochemistry 2001; 40:15464-70. [PMID: 11747421 DOI: 10.1021/bi015864r] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.5] [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: 11/28/2022]
Abstract
Cassette replacement of acyltransferase (AT) domains in 6-deoxyerythronolide B synthase (DEBS) with heterologous AT domains with different substrate specificities usually yields the predicted polyketide analogues. As reported here, however, several AT replacements in module 4 of DEBS failed to produce detectable polyketide under standard conditions, suggesting that module 4 is sensitive to perturbation of the protein structure when the AT is replaced. Alignments between different modular polyketide synthase AT domains and the Escherichia coli fatty acid synthase transacylase crystal structure were used to select motifs within the AT domain of module 4 to re-engineer its substrate selectivity and minimize potential alterations to protein folding. Three distinct primary regions of AT4 believed to confer specificity for methylmalonyl-CoA were mutated into the sequence seen in malonyl-CoA-specific domains. Each individual mutation as well as the three in combination resulted in functional DEBSs that produced mixtures of the natural polyketide, 6-deoxyerythronolide B, and the desired novel analogue, 6-desmethyl-6-deoxyerythronolide B. Production of the latter compound indicates that the identified sequence motifs do contribute to AT specificity and that DEBS can process a polyketide chain incorporating a malonate unit at module 4. This is the first example in which the extender unit specificity of a PKS module has been altered by site-specific mutation and provides a useful alternate method for engineering AT specificity in the combinatorial biosynthesis of polyketides.
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Affiliation(s)
- C D Reeves
- Kosan Biosciences, Inc., 3832 Bay Center Place, Hayward, California 94545, USA
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Hutchinson CR, McDaniel R. Combinatorial biosynthesis in microorganisms as a route to new antimicrobial, antitumor and neuroregenerative drugs. Curr Opin Investig Drugs 2001; 2:1681-90. [PMID: 11892929] [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: 02/24/2023]
Abstract
Combinatorial biosynthesis utilizes the genes of biosynthetic pathways that produce microbial products to create novel chemical structures. The engineering of mondular polyketide synthase (PKS) genes has been the major focus of this effort and has led to the production of analogs of macrolide antibiotics like the erythromycins and their derived ketolides, and of the immunosuppressive macrolide FK-520 (Fujisawa Pharmaceutical Co Ltd). Approaches to making analogs of the promising antitumor compounds known as epothilones are also being explored. Lead compounds for further study have resulted and routes to analogs of other pharmacologically important compounds have been established. To facilitate this work, many new tools for manipulating and studying the multifunctional PKSs have been developed including the development of Escherichia coli as a PKS expression last. These developments have resulted in faster ways of engineering PKS to produce new compounds for the development of chemotherapeutic agents from natural products.
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Wagner KA, McDaniel R, Self D. Collection and preparation of sidestream cigarette smoke for trace elemental determinations by graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry. J AOAC Int 2001; 84:1934-40. [PMID: 11767165] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
A novel method for the collection and preparation of sidestream cigarette smoke condensate is described for trace elemental analysis by inductively coupled plasma mass spectrometry and graphite furnace atomic absorption spectrometry. The smoke collection method utilizes a specially designed chimney that collects and directs the sidestream smoke (SS) to a 2-stage trapping system consisting of an impaction trap followed by a 0.8 microm mixed cellulose ester filter. The samples are digested with nitric acid in a commercial heating block before analysis. The method limits of detection (LODs) are 1, 0.2, 2, 9, 6, and 7 ng/cigt for As, Cd, Pb, Ni, Se, and Cr, respectively. The SS collected from an industry reference cigarette, 1R4F, produced by the University of Kentucky was analyzed. The concentrations of As, Cd, and Pb in 1R4F were determined to be 27.3+/-2.1, 412+/-14, and 43.8+/-2.0 ng/cigt, respectively, while the concentrations of Ni, Cr, and Se are below the method LOD. Consequently, this novel method successfully addresses contamination, instrumentation, and collection issues for performing trace elemental analysis of sidestream cigarette smoke condensate.
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Abstract
Combinatorial biosynthesis utilizes the enzymes from antibiotic (and other natural product) biosynthetic pathways to create novel chemical structures. The manipulation of modular polyketide synthases (PKSs) has been the major focus of this effort and has led to the production of, for example, several erythromycin analogs. Many new tools for manipulating and studying these multifunctional enzymes have been developed. These include multiple hosts and expression systems, enzymology tools for in vitro study, and ways to engineer pre-PKS and post-PKS pathways. The result is more rational and faster methods of engineering new compounds for the development of chemotherapeutic agents from natural products. The most significant recent advances in combinatorial biosynthesis are outlined.
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Affiliation(s)
- E Rodriguez
- Kosan Biosciences Inc, 3832 Bay Center Place, Hayward, CA 94545, USA.
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11
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Abstract
BACKGROUND Combinatorial biosynthesis techniques using polyketide synthases (PKSs) in heterologous host organisms have enabled the production of macrolide aglycone libraries in which many positions of the macrolactone ring have been manipulated. However, the deoxysugar moieties of macrolides, absent in previous libraries, play a critical role in contributing to the antimicrobial properties exhibited by compounds such as erythromycin. Since the glycosidic components of polyketides dramatically alter their molecular binding properties, it would be useful to develop general expression hosts and vectors for synthesis and attachment of deoxysugars to expand the nature and size of such polyketide libraries. RESULTS A set of nine deoxysugar biosynthetic and auxiliary genes from the picromycin/methymycin (pik) cluster was integrated in the chromosome of Streptomyces lividans to create a host which synthesizes TDP-D-desosamine. The pik desosaminyl transferase was also included so that when the strain was transformed with a previously constructed library of expression plasmids encoding genetically modified PKSs that produce different macrolactones, the resulting strains produced desosaminylated derivatives. Although conversion of the macrolactones was generally low, bioassays revealed that, unlike their aglycone precursors, these novel macrolides possessed antibiotic activity. CONCLUSIONS Based on the structural differences among the compounds that were glycosylated it appears that the desosaminyl transferase from the pik gene cluster is quite tolerant of changes in the macrolactone substrate. Since others have demonstrated tolerance towards modifications in the sugar substituent, one can imagine employing this approach to alter both polyketide and deoxysugar pathways to produce 'unnatural' natural product libraries.
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Affiliation(s)
- L Tang
- KOSAN Biosciences, Inc., 3832 Bay Center Place, 94545, Hayward, CA, USA
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Mock V, Pickett M, Ropka ME, Muscari Lin E, Stewart KJ, Rhodes VA, McDaniel R, Grimm PM, Krumm S, McCorkle R. Fatigue and quality of life outcomes of exercise during cancer treatment. Cancer Pract 2001; 9:119-27. [PMID: 11879296 DOI: 10.1046/j.1523-5394.2001.009003119.x] [Citation(s) in RCA: 341] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
PURPOSE Despite the recognition of fatigue as a common and distressing symptom during cancer treatment, there are few evidence-based interventions available to manage such fatigue. The purpose of this multi-institutional pilot study was to explore the effects of a home-based moderate walking exercise intervention on fatigue, physical functioning, emotional distress, and quality of life (QOL) during breast cancer treatment. DESCRIPTION OF STUDY Fifty-two women were recruited from five university hospital outpatient departments for this pilot study with an experimental design. Subjects were randomly assigned to the walking program or to usual care during adjuvant chemotherapy or radiation therapy for breast cancer. Symptoms, physical functioning, and QOL were measured at baseline, midtreatment, and at the end of treatment. RESULTS Women who exercised at least 90 minutes per week on 3 or more days reported significantly less fatigue and emotional distress as well as higher functional ability and QOL than women who were less active during treatment. CLINICAL IMPLICATIONS A home-based walking exercise program is a potentially effective, low-cost, and safe intervention to manage fatigue and to improve QOL during adjuvant chemotherapy or radiation therapy for breast cancer. This health-promoting self-care activity needs further testing in large randomized clinical trials.
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Affiliation(s)
- V Mock
- The Johns Hopkins University School of Nursing, Baltimore, Maryland 21211-4250, USA
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Volchegursky Y, Hu Z, Katz L, McDaniel R. Biosynthesis of the anti-parasitic agent megalomicin: transformation of erythromycin to megalomicin in Saccharopolyspora erythraea. Mol Microbiol 2000; 37:752-62. [PMID: 10972798 DOI: 10.1046/j.1365-2958.2000.02059.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [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: 11/20/2022]
Abstract
Megalomicin is a therapeutically diverse compound which possesses antiparasitic, antiviral and antibacterial properties. It is produced by Micromonospora megalomicea and differs from the well-known macrolide antibiotic erythromycin by the addition of a unique deoxyamino sugar, megosamine, to the C-6 hydroxyl. We have cloned and sequenced a 48 kb segment of the megalomicin (meg) biosynthetic gene cluster which contains the modular polyketide synthase (PKS) and the complete pathway for megosamine biosynthesis. The similarities and distinctions between the related megalomicin and erythromycin gene clusters are discussed. Heterologous expression of the megalomicin PKS in Streptomyces lividans led to production of 6-deoxyerythronolide B, the same macrolactone intermediate for erythromycin. A 12 kb fragment harbouring the putative megosamine pathway was expressed in Saccharopolyspora erythraea, resulting in the conversion of erythromycin to megalomicin. Considering the extensive knowledge surrounding the genetic engineering of the erythromycin PKS and the familiarity with genetic manipulation and fermentation of S. erythraea, the ability to produce megalomicin in this strain should allow the engineering of novel megalomicin analogues with potentially improved therapeutic activities.
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Shah S, Xue Q, Tang L, Carney JR, Betlach M, McDaniel R. Cloning, characterization and heterologous expression of a polyketide synthase and P-450 oxidase involved in the biosynthesis of the antibiotic oleandomycin. J Antibiot (Tokyo) 2000; 53:502-8. [PMID: 10908114 DOI: 10.7164/antibiotics.53.502] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [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: 11/21/2022]
Abstract
The gene cluster encoding the deoxyoleandolide polyketide synthase (OlePKS) was isolated from the oleandomycin producing strain Streptomnyces antibioticus. Sequencing of the first two genes encoding OlePKS, together with the previously identified third gene revealed an overall genetic and protein architecture similar to that of the erythromycin gene cluster encoding the 6-deoxyerythronolide B synthase (DEBS) from Saccharopolyspora erythraea. When the entire OlePKS (10,487 amino acids) was expressed in the heterologous host Streptomyces lividans, it produced 8,8a-deoxyoleandolide, an aglycone precursor of oleandomycin. The role of the P-450 monooxygenase, OleP, in oleandomycin biosynthesis was also examined in vivo by co-expression with DEBS in S. lividans. The production of 8,8a-dihydroxy-6-deoxyerythronolide B and other derivatives indicates that OleP is involved in the epoxidation pathway of oleandomycin biosynthesis. Since there are currently no genetic systems available for manipulation of the natural oleandomycin producing strain, the heterologous expression system reported here provides a useful tool for studying this important macrolide antibiotic.
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Affiliation(s)
- S Shah
- Kosan Biosciences Inc, Hayward, CA 94545, USA
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Sonenshine DE, Allan SA, Peter TF, McDaniel R, Burridge MJ. Does geographic range affect the attractant-aggregation-attachment pheromone of the tropical bont tick, amblyomma variegatum? Exp Appl Acarol 2000; 24:283-299. [PMID: 11110239 DOI: 10.1023/a:1006479118160] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The tropical bont tick, Amblyomma variegatum, transmits heartwater in sub-Saharan Africa and in the Caribbean. This species has a broad geographic distribution, ranging from Madagascar and other islands in the Indian Ocean through most of sub-Saharan Africa, to several islands in the eastern Caribbean Sea. Blood fed male A. variegatum secrete an attraction-aggregation-attachment (AAA) pheromone which, combined with CO2, excites host finding and formation of feeding clusters of these ticks. However, it is not known whether the composition of the pheromone varies throughout A. variegatum's geographic range. Extracts of fed male ticks were examined for phenols and volatile organic acids by gas chromatography and mass spectrometry to determine whether differences occur in the pheromone components of populations of this species across the geographic range (Guadeloupe, Zimbabwe, Zambia and Rwanda). No significant difference in the chemical composition of the pheromone in relation to geographic range was found. No significant differences in rates of attachment in response to native versus foreign extracts were found in on-host attachment tests comparing ticks from two countries. Guadeloupe (Caribbean) and Zimbabwe (African). This finding was confirmed in more detailed studies with ticks from Guadeloupe and four African countries (Kenya, Rwanda, Zambia and Zimbabwe). On-host attachment assays from these countries did not detect consistent differences in response to extracts from different locations. In an olfactometer bioassay, females were not consistently more attracted to extracts from their native locality than from any of the foreign localities. We conclude that despite the widespread distribution of A. variegatum over both hemispheres, no significant differences in pheromone composition or biological responses to male tick pheromone secretions occur.
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Affiliation(s)
- D E Sonenshine
- Department of Biological Sciences, Old Dominion University, Norfolk, Virginia 23529, USA.
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Tang L, Fu H, McDaniel R. Formation of functional heterologous complexes using subunits from the picromycin, erythromycin and oleandomycin polyketide synthases. Chem Biol 2000; 7:77-84. [PMID: 10662693 DOI: 10.1016/s1074-5521(00)00073-9] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND Recently developed tools for the genetic manipulation of modular polyketide synthases (PKSs) have advanced the development of combinatorial biosynthesis technologies for drug discovery. Although many of the current techniques involve engineering individual domains or modules of the PKS, few experiments have addressed the ability to combine entire protein subunits from different modular PKSs to create hybrid polyketide pathways. We investigated this possibility by in vivo assembly of heterologous PKS complexes using natural and altered subunits from related macrolide PKSs. RESULTS The pikAI and pikAII genes encoding subunits 1 and 2 (modules 1-4) of the picromycin PKS (PikPKS) and the eryAIII gene encoding subunit 3 (modules 5-6) of the 6-deoxyerythronolide B synthase (DEBS) were cloned in two compatible Streptomyces expression vectors. A strain of Streptomyces lividans co-transformed with the two vectors produced the hybrid macrolactone 3-hydroxynarbonolide. Co-expression of the same pik genes with the gene for subunit 3 of the oleandomycin PKS (OlePKS) was also successful. A series of hybrid polyketide pathways was then constructed by combining PikPKS subunits 1 and 2 with modified DEBS3 subunits containing engineered domains in modules 5 or 6. We also report the effect of junction location in a set of DEBS-PikPKS fusions. CONCLUSIONS We show that natural as well as engineered protein subunits from heterologous modular PKSs can be functionally assembled to create hybrid polyketide pathways. This work represents a new strategy that complements earlier domain engineering approaches for combinatorial biosynthesis in which complete modules or PKS protein subunits, in addition to individual enzymatic domains, are used as building blocks for PKS engineering.
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Affiliation(s)
- L Tang
- Incorporated, KOSAN Biosciences, Hayward, CA 94545, USA. tang@kosan. com
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17
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Abstract
Erythromycin, a complex polyketide antibiotic belonging to the macrolide class, is produced as a natural product by the bacterium Saccharopolyspora erythraea. The genes encoding the enzymes responsible for the synthesis of the antibiotic have been cloned and sequenced, revealing that the polyketide backbone of the molecule in produced by a polyketide synthase (PKS) composed of multifunctional proteins that contain discrete functional domains for each step of synthesis. Genetic manipulation of the PKS-encoding genes can result in predictable changes in the structure of the polyketide component of erythromycin, many of which are not easily achievable through standard chemical derivatization or synthesis. Many of the changes can be combined to lead to the further generation of navel structures. Whereas genetic engineering of the erythromycin structure has been practiced for a number of years, the re cent and continuing discoveries of modular PKSs for the synthesis of many other important complex polyketides has raised the possibility of generating novel structures in these molecules by genetic manipulation, as well.
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Affiliation(s)
- L Katz
- Kosan Biosciences, Inc., Hayward, California 94545, USA.
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18
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Tang L, Fu H, Betlach MC, McDaniel R. Elucidating the mechanism of chain termination switching in the picromycin/methymycin polyketide synthase. Chem Biol 1999; 6:553-8. [PMID: 10421766 DOI: 10.1016/s1074-5521(99)80087-8] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
BACKGROUND A single modular polyketide synthase (PKS) gene cluster is responsible for production of both the 14-membered macrolide antibiotic picromycin and the 12-membered macrolide antibiotic methymycin in Streptomyces venezuelae. Building on the success of the heterologous expression system engineered using the erythromycin PKS, we have constructed an analogous system for the picromycin/methymycin PKS. Through heterologous expression and construction of a hybrid PKS, we have examined the contributions that the PKS, its internal thioesterase domain (pikTE) and the Pik TEII thioesterase domain make in termination and cyclization of the two polyketide intermediates. RESULTS The picromycin/methymycin PKS genes were functionally expressed in the heterologous host Streptomyces lividans, resulting in production of both narbonolide and 10-deoxymethynolide (the precursors of picromycin and methymycin, respectively). Co-expression with the Pik TEII thioesterase led to increased production levels, but did not change the ratio of the two compounds produced, leaving the function of this protein largely unknown. Fusion of the PKS thioesterase domain (pikTE) to 6-deoxyerythronolide B synthase (DEBS) resulted in formation of only 14-membered macrolactones. CONCLUSIONS These experiments demonstrate that the PKS alone is capable of catalyzing the synthesis of both 14- and 12-membered macrolactones and favor a model by which different macrolactone rings result from a combination of the arrangement between the module 5 and module 6 subunits in the picromycin PKS complex and the selectivity of the pikTE domain.
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Affiliation(s)
- L Tang
- KOSAN Biosciences, Inc., 3832 Bay Center Place, Hayward, CA 94545, USA
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McDaniel R, Thamchaipenet A, Gustafsson C, Fu H, Betlach M, Ashley G. Multiple genetic modifications of the erythromycin polyketide synthase to produce a library of novel "unnatural" natural products. Proc Natl Acad Sci U S A 1999; 96:1846-51. [PMID: 10051557 PMCID: PMC26699 DOI: 10.1073/pnas.96.5.1846] [Citation(s) in RCA: 318] [Impact Index Per Article: 12.7] [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: 11/18/2022] Open
Abstract
The structures of complex polyketide natural products, such as erythromycin, are programmed by multifunctional polyketide synthases (PKSs) that contain modular arrangements of functional domains. The colinearity between the activities of modular PKS domains and structure of the polyketide product portends the generation of novel organic compounds-"unnatural" natural products-by genetic manipulation. We have engineered the erythromycin polyketide synthase genes to effect combinatorial alterations of catalytic activities in the biosynthetic pathway, generating a library of >50 macrolides that would be impractical to produce by chemical methods. The library includes examples of analogs with one, two, and three altered carbon centers of the polyketide products. The manipulation of multiple biosynthetic steps in a PKS is an important milestone toward the goal of producing large libraries of unnatural natural products for biological and pharmaceutical applications.
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Affiliation(s)
- R McDaniel
- KOSAN Biosciences, Inc., 1450 Rollins Road, Burlingame, CA 94010, USA.
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20
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Graziani EI, Cane DE, Betlach MC, Kealey JT, McDaniel R. Macrolide biosynthesis: a single cytochrome P450, PicK, is responsible for the hydroxylations that generate methymycin, neomethymycin, and picromycin in Streptomyces venezuelae. Bioorg Med Chem Lett 1998; 8:3117-20. [PMID: 9873687 DOI: 10.1016/s0960-894x(98)00553-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [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: 11/26/2022]
Abstract
The final step in the biosynthesis of methymycin, neomethymycin, and picromycin is an hydroxylation, shown to be carried out by the cytochrome P-450 monooxygenase, PicK. Direct comparison of the relative Kcat/K(m) values for the two substrates, YC-17 and narbomycin, showed a threefold rate preference of picK for narbomycin.
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Affiliation(s)
- E I Graziani
- Department of Chemistry, Brown University, Providence, RI 02912-9108, USA
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Betlach MC, Kealey JT, Ashley GW, McDaniel R. Characterization of the macrolide P-450 hydroxylase from Streptomyces venezuelae which converts narbomycin to picromycin. Biochemistry 1998; 37:14937-42. [PMID: 9778370 DOI: 10.1021/bi981699c] [Citation(s) in RCA: 46] [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: 11/29/2022]
Abstract
The post-polyketide synthase (PKS) biosynthetic tailoring of macrolide antibiotics usually involves one or more oxidation reactions catalyzed by cytochrome P450 monooxygenases. As the specificities of members from this class of enzymes vary significantly among PKS gene clusters, the identification and study of new macrolide P450s are important to the growing field of combinatorial biosynthesis. We have isolated the cytochrome P450 gene picK from Streptomyces venezuelae which is responsible for the C-12 hydroxylation of narbomycin to picromycin. The gene was located by searching regions proximal to modular PKS genes with a probe for macrolide P450 monooxygenases. The overproduction of PicK with a C-terminal six-His affinity tag (PicK/6-His) in Escherichia coli aided the purification of the enzyme for kinetic analysis. PicK/6-His was shown to catalyze the in vitro C-12 hydroxylation of narbomycin with a kcat of 1.4 s-1, which is similar to the value reported for the related C-12 hydroxylation of erythromycin D by the EryK hydroxylase. The unique specificity of this enzyme should be useful for the modification of novel macrolide substrates similar to narbomycin, in particular, ketolides, a promising class of semisynthetic macrolides with activity against erythromycin-resistant pathogens.
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Affiliation(s)
- M C Betlach
- KOSAN Biosciences, Inc., Burlingame, California 94010, USA
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22
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Mock V, Ropka ME, Rhodes VA, Pickett M, Grimm PM, McDaniel R, Lin EM, Allocca P, Dienemann JA, Haisfield-Wolfe ME, Stewart KJ, McCorkle R. Establishing mechanisms to conduct multi-institutional research--fatigue in patients with cancer: an exercise intervention. Oncol Nurs Forum 1998; 25:1391-7. [PMID: 9766292] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
PURPOSES/OBJECTIVES To describe the process of establishing a multi-institutional interdisciplinary team of oncology researchers and conducting a pilot study of an exercise intervention for fatigue. DATA SOURCES Project meeting minutes and records, research team members' logs, subjects' research records, the research study proposal, and team members' individual and collective shared experiences. DATA SYNTHESIS Site investigators established research teams at five academic medical centers. Fifty subjects were enrolled in the study and tested during their cancer treatment. Study methods, including instrumentation, were evaluated carefully and revised. CONCLUSIONS The multi-institutional network of researchers is an effective and efficient model for testing an intervention to manage fatigue during cancer treatment. IMPLICATIONS FOR NURSING PRACTICE Exercise is a feasible and potentially beneficial intervention to combat distressing cancer treatment-related fatigue. A pilot study is essential to determine the best methods for conducting a clinical trial and to develop the teams of researchers necessary for such a project.
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Affiliation(s)
- V Mock
- Johns Hopkins Hospital, Baltimore, MD, USA
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23
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Miller WL, Crabtree BF, McDaniel R, Stange KC. Understanding change in primary care practice using complexity theory. J Fam Pract 1998; 46:369-376. [PMID: 9597994] [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] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
BACKGROUND Understanding the organization of primary care practices is essential for implementing changes related to delivery of preventive or other health care services. A theoretical model derived from complexity theory provides a framework for understanding practice change. METHODS Data were reviewed from brief participant observation fieldnotes collected in the 84 practices of the Direct Observation of Primary Care (DOPC) study and in 27 practices from three similar studies investigating preventive services delivery. These data were synthesized with information from an extensive search of the social science, nursing, and health services literature concerning practice organization, and of the literature on complexity theory from the fields of mathematics, physics, biology, management, medicine, and family systems, to create a complexity model of primary care practice. RESULTS Primary care practices are understood as complex adaptive systems consisting of agents, such as patients, office staff, and physicians, who enact internal models of income generation, patient care, and organizational operations. These internal models interact dynamically to create each unique practice. The particular shape of each practice is determined by its primary goals. The model suggests three strategies for promoting change in practice and practitioner behavior: joining, transforming, and learning. CONCLUSIONS This model has important implications for understanding change in primary care practice. Practices are much more complex than present strategies for change assume. The complexity model identified why some strategies work in particular practices and others do not.
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Affiliation(s)
- W L Miller
- Lehigh Valley Hospital, Department of Family Practice, Allentown, PA 18104, USA
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24
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Abstract
BACKGROUND Modular polyketide synthases (PKSs) are very large multifunctional enzyme complexes that synthesize a number of medicinally important natural products. The modular arrangement of active sites has made these enzyme systems amenable to combinatorial manipulation for the biosynthesis of novel polyketides. Here, we investigate the involvement of subunit interactions in hybrid and artificially linked PKSs with several series of intermodular and intramodular fusions using the erythromycin (6-deoxyerythronolide B synthase; DEBS) and rapamycin (RAPS) PKSs. RESULTS Several two-module and three-module derivatives of DEBS were constructed by fusing module 6 to either module 2 or module 3 at varying junctions. Polyketide production by these intramodular fusions indicated that the core set of active sites remained functional in these hybrid modules, although the ketoreductase domain of module 6 was unable to recognize unnatural triketide and tetraketide substrates. Artificial trimodular PKS subunits were also engineered by covalently linking modules 2 and 3 of DEBS, thereby demonstrating the feasibility of constructing single-chain PKSs. Finally, a series of fusions containing DEBS and RAPS domains in module 2 of an engineered trimodular PKS revealed the structural and functional tolerance for hybrid modules created from distinct PKS gene clusters. CONCLUSIONS The general success of the intermodular and intramodular fusions described here demonstrates significant structural tolerance among PKS modules and subunits and suggests that substrate specificity, rather than protein-protein interactions, is the primary determinant of molecular recognition features of PKSs. Furthermore, the ability to artificially link modules may considerably simplify the heterologous expression of modular PKSs in higher eukaryotic systems.
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Affiliation(s)
- R McDaniel
- KOSAN Biosciences, Inc., Burlingame, CA 94010, USA.
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25
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Abstract
OBJECTIVES To evaluate the impact of changing population demographics on urologic staffing over the coming decades. METHODS A model was constructed using data obtained from the U.S. Bureau of the Census for population projections; clinical studies to assess the percentages of men with symptomatic benign prostatic hyperplasia (BPH) and those undergoing prostatectomy; the American Medical Association regarding numbers and annual percent change of practicing urologists; and the American Urological Association regarding numbers of physicians completing residency training programs. Sensitivity analyses were performed varying both the rate of surgical intervention for symptomatic BPH and the annual increase in the number of practicing urologists. RESULTS Regardless of variations in the surgical rate to as low as 4%, the average number of transurethral resections of the prostate gland/surgical interventions for BPH per urologist will increase by the year 2020 when compared with the known basepoint value obtained for 1990. Additionally, even with an annual net increase of 200 urologists per year, by 2020, the rapidly expanding population over 65 years of age will nearly offset even such a large increase in the number of practicing urologists. CONCLUSIONS The greatest factor concerning future urologic staffing issues will be the changing population demographics. The need for urologic services will continue to rise. An oversupply of urologists can be avoided as long as the net increase does not exceed an average of 200 urologists annually.
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Affiliation(s)
- D M Weiner
- Department of Urology, Columbia University College of Physicians and Surgeons, New York, New York 10019, USA
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26
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McDaniel R. Unintended consequences. State Health Care Am 1996:49-50. [PMID: 10168087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Affiliation(s)
- R McDaniel
- College of Business Administration, University of Texas at Austin, USA
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McDaniel R, Ebert-Khosla S, Hopwood DA, Khosla C. Rational design of aromatic polyketide natural products by recombinant assembly of enzymatic subunits. Nature 1995; 375:549-54. [PMID: 7791871 DOI: 10.1038/375549a0] [Citation(s) in RCA: 233] [Impact Index Per Article: 8.0] [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: 01/27/2023]
Abstract
Recent advances in understanding of bacterial aromatic polyketide biosynthesis allow the development of a set of design rules for the rational manipulation of chain synthesis, reduction of keto groups and early cyclization steps by genetic engineering. The concept of rational design is illustrated by the preparation of Streptomyces strains that produce two new polyketides by expression of combinations of appropriate enzymatic subunits from naturally occurring polyketide synthases. The potential for generating molecular diversity within this class of molecules by genetic engineering is enormous.
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Affiliation(s)
- R McDaniel
- Department of Chemical Engineering, Stanford University, California 94305-5025, USA
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28
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McDaniel R, Ebert-Khosla S, Fu H, Hopwood DA, Khosla C. Engineered biosynthesis of novel polyketides: influence of a downstream enzyme on the catalytic specificity of a minimal aromatic polyketide synthase. Proc Natl Acad Sci U S A 1994; 91:11542-6. [PMID: 7972098 PMCID: PMC45267 DOI: 10.1073/pnas.91.24.11542] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.3] [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: 01/28/2023] Open
Abstract
To identify the minimum set of polyketide synthase (PKS) components required for in vivo biosynthesis of aromatic polyketides, combinations of genes encoding subunits of three different aromatic PKSs--act from Streptomyces coelicolor A3(2) (an actinorhodin producer), fren from Streptomyces roseofulvus (a frenolicin and nanaomycin producer), and tcm from Streptomyces glaucescens (a tetracenomycin producer)--were expressed in a recently developed Streptomyces host-vector system. The "minimal" components (ketosynthase/putative acyltransferase, chain length-determining factor, and acyl carrier protein) were produced with and without a functional polyketide ketoreductase and/or cyclase, and the polyketide products of these recombinant strains were structurally characterized. Several previously identified polyketides were isolated in addition to two previously unidentified polyketides, dehydromutactin and SEK 15b, described here. The results proved that the act cyclase is not required for the biosynthesis of several aberrantly cyclized products that have been previously reported. They are also consistent with earlier conclusions that the minimal PKS controls chain length as well as the regiospecificity of the first cyclization and that it can do so in the absence of both a ketoreductase and a cyclase. However, the ability of the minimal tcm PKS to synthesize two different singly cyclized intermediates suggests that it is unable to accurately control the course of this reaction by itself. In the presence of a downstream enzyme, the flux through one branch of the cyclization pathway increases relative to the other. We propose that these alternative specificities may be due to the ability of downstream enzymes to associate with the minimal PKS and to selectively inhibit a particular branch of the cyclization pathway.
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Affiliation(s)
- R McDaniel
- Department of Chemical Engineering, Stanford University, CA 94305-5025
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Fu H, McDaniel R, Hopwood DA, Khosla C. Engineered biosynthesis of novel polyketides: stereochemical course of two reactions catalyzed by a polyketide synthase. Biochemistry 1994; 33:9321-6. [PMID: 8049233 DOI: 10.1021/bi00197a036] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [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: 01/28/2023]
Abstract
A genetically engineered strain expressing the essential components of the tetracenomycin polyketide synthase (tcm PKS) along with the actinorhodin ketoreductase (act KR) was found to produce two new (diastereomeric) aromatic polyketides, designated RM20b and RM20c, in addition to RM20, whose structure was reported earlier [McDaniel, R., Ebert-Khosla, S., Hopwood, D. A., & Khosla, C. (1993) Science 262, 1546-1550]. Spectroscopic and in vivo isotopic labeling analysis of RM20b and RM20c revealed that their polyketide backbones were identical to that of RM20 with respect to chain length, regiospecificity of ketoreduction, and regiospecificity of the first intramolecular aldol condensation. This is consistent with earlier predictions that the essential components of the PKS--a bifunctional ketosynthase/acyltransferase, a chain length determining factor, and an acyl carrier protein--are responsible for controlling each of these features of the polyketide backbone [McDaniel, R., Ebert-Khosla, S., Hopwood, D. A., & Khosla, C. (1993) Science 262, 1546-1550; McDaniel, R., Ebert-Khosla, S., Hopwood, D. A., & Khosla, C. (1993) J. Am. Chem. Soc. 115, 11671-11675; Fu, H., Ebert-Khosla, S., Hopwood, D. A., & Khosla, C. (1994) J. Am. Chem. Soc. 116, 4166-4170]. In addition, however, RM20b and RM20c possess two unusual features. In both molecules the hydroxyls on sp3 C-9 and C-7 of the first six-membered ring, which arise as a result of ketoreduction and aldol condensation, respectively, are intact, rather than being lost via dehydration. Furthermore, the relative yield of RM20b (in which these hydroxyls are syn) is 7-fold greater than that of RM20c (in which they are anti).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- H Fu
- Department of Chemical Engineering, Stanford University, California 94305-5025
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30
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Abstract
Polyketide synthases (PKSs) are multifunctional enzymes that catalyze the biosynthesis of a huge variety of carbon chains differing in their length and patterns of functionality and cyclization. Many polyketides are valuable therapeutic agents. A Streptomyces host-vector system has been developed for efficient construction and expression of recombinant PKSs. Using this expression system, several novel compounds have been synthesized in vivo in significant quantities. Characterization of these metabolites has provided new insights into key features of actinomycete aromatic PKS specificity. Thus, carbon chain length is dictated, at least in part, by a protein that appears to be distinctive to this family of PKSs, whereas the acyl carrier proteins of different PKSs can be interchanged without affecting product structure. A given ketoreductase can recognize and reduce polyketide chains of different length; this ketoreduction always occurs at the C-9 position. The regiospecificity of the first cyclization of the nascent polyketide chain is either determined by the ketoreductase, or the chain-extending enzymes themselves. However, the regiospecificity of the second cyclization is determined by a distinct cyclase, which can discriminate between substrates of different chain lengths.
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Affiliation(s)
- R McDaniel
- Department of Chemical Engineering, Stanford University, CA 94305-5025
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31
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Abstract
Although heart mitochondria contain glutamate dehydrogenase, it has not been thought to play a role in their metabolism. We investigated this matter to define the conditions under which it is active. We found modest activity in the presence of glutamate and malate and a continuous source of ADP when pyruvate is added. This increases several fold as the osmolarity is increased from 296 to 370 mosM. At the higher osmolarity ammonia formation is brief, associated with a lower intramitochondrial alpha-ketoglutarate from citrate does not make up for the drop in glutamate conversion to alpha-ketoglutarate. Mitochondrial content of nucleotides and CoA compounds are not altered by pyruvate addition. The rate of glutamate deamination by GDH in sonicated heart mitochondria agrees with the rate of ammonia formation in intact mitochondria in the presence of pyruvate (20 nmol/min/mg of mitochondrial protein). We conclude pyruvate lowers mitochondrial oxalacetate which decreases alpha-ketoglutarate formation by transamination. The lower mitochondria alpha-ketoglutarate level permits glutamate deamination until alpha-ketoglutarate reaches a level that inhibits the forward reaction. Further proof of the key role of alpha-ketoglutarate is seen with aminooxyacetate which blocks transamination. In its presence ammonia formation occurs at the same rate (18 nm/min/mg of mitochondrial protein), is not dependent upon pyruvate, and does not stop after a couple of minutes. Leucine, which decreases alpha-ketoglutarate inhibition of GDH, also results in ammonia formation, further supporting the concept of regulation by alpha-ketoglutarate. The higher osmolarity increases GDH activity by increasing alpha-ketoglutarate transport from mitochondria.
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Cohen PL, Creech E, Nakul-Aquaronne D, McDaniel R, Ackler S, Rapoport RG, Sobel ES, Eisenberg RA. Antigen nonspecific effect of major histocompatibility complex haplotype on autoantibody levels in systemic lupus erythematosus-prone lpr mice. J Clin Invest 1993; 91:2761-8. [PMID: 7685774 PMCID: PMC443342 DOI: 10.1172/jci116517] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [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: 01/26/2023] Open
Abstract
MHC-linked genes strongly influence susceptibility to autoimmune diseases and also regulate responses to exogenous antigens. To begin to understand the mechanism of this MHC effect on disease, we have investigated MHC-congenic mouse strains that develop spontaneous autoimmunity because of the lpr gene. C57BL6/lpr (B6/lpr) mice (H-2b) are known to have substantial levels of autoantibodies to chromatin, single stranded DNA (ssDNA3), and IgG of different murine subclasses (rheumatoid factor). We have crossed the H-2d and the H-2bm12 (la mutant) haplotypes onto the B6/lpr background. Surprisingly, levels of all the autoantibodies were markedly lower in B6/lpr.H-2d, but levels in B6/lpr.H-2bm12 were no different from those in B6/lpr mice. The downregulating influence of the H-2d allele was dominant, and there was no effect on autoantibody fine specificities. The genetics of the H-2d effect and its diffuse influence on multiple autoantibody specificities, in addition to the lack of effect of the bm12 mutation, which modifies the peptide-binding groove of I-A, together raise the question of whether MHC-linked genes other than classical (IR) genes may be responsible for MHC disease associations in this model.
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Affiliation(s)
- P L Cohen
- Department of Medicine, University of North Carolina School of Medicine, Chapel Hill 27599-7280
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Khosla C, McDaniel R, Ebert-Khosla S, Torres R, Sherman DH, Bibb MJ, Hopwood DA. Genetic construction and functional analysis of hybrid polyketide synthases containing heterologous acyl carrier proteins. J Bacteriol 1993; 175:2197-204. [PMID: 8468280 PMCID: PMC204504 DOI: 10.1128/jb.175.8.2197-2204.1993] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.4] [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: 01/30/2023] Open
Abstract
The gene that encodes the acyl carrier protein (ACP) of the actinorhodin polyketide synthase (PKS) of Streptomyces coelicolor A3(2) was replaced with homologs from the granaticin, oxytetracycline, tetracenomycin, and putative frenolicin polyketide synthase gene clusters. All of the replacements led to expression of functional synthases, and the recombinants synthesized aromatic polyketides similar in chromatographic properties to actinorhodin or to shunt products produced by mutants defective in the actinorhodin pathway. Some regions within the ACP were also shown to be interchangeable and allow production of a functional hybrid ACP. Structural analysis of the most abundant polyketide product of one of the recombinants by electrospray mass spectrometry suggested that it is identical to mutactin, a previously characterized shunt product of an actVII mutant (deficient in cyclase and dehydrase activities). Quantitative differences in the product profiles of strains that express the various hybrid synthases were observed. These can be explained, at least in part, by differences in ribosome-binding sites upstream of each ACP gene, implying either that the ACP concentration in some strains is rate limiting to overall PKS activity or that the level of ACP expression also influences the expression of another enzyme(s) encoded by a downstream gene(s) in the same operon as the actinorhodin ACP gene. These results reaffirm the idea that construction of hybrid polyketide synthases will be a useful approach for dissecting the molecular basis of the specificity of PKS-catalyzed reactions. However, they also point to the need for reducing the chemical complexity of the approach by minimizing the diversity of polyketide products synthesized in strains that produce recombinant polyketide synthases.
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Affiliation(s)
- C Khosla
- Department of Genetics, John Innes Institute, John Innes Centre, Norwich, United Kingdom
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34
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Abstract
We studied the binding of calcium to bilayer membranes formed from mixtures of phosphatidylcholine and mono-, di-, or trisialoganglioside by measuring its effect on the electrophoretic mobility of multilamellar vesicles and the conductance of planar bilayers. In 0.001 M monovalent salt solutions the surface potential of the membranes is large and micromolar concentrations of calcium have a significant effect on the mobility and conductance. In 0.1 M monovalent salt solutions the surface potential is small and millimolar concentrations of calcium are required to affect these parameters. The strong apparent binding of calcium we observed at low ionic strength could be due to the nonspecific accumulation of calcium in the electrical diffuse double layer. To distinguish between this nonspecific effect and binding of calcium to the membrane, we substituted dimethonium for calcium. Dimethonium is a divalent cation that screens negative charges but does not bind to lipids. We also examined the effect of replacing phosphatidylcholine by monoolein: calcium binds to phosphatidylcholine but not to monoolein. We describe our electrophoretic mobility results by combining the Poisson-Boltzmann and Navier-Stokes equations with the Langmuir adsorption isotherm. We conclude that calcium binds weakly to gangliosides with an intrinsic association constant of less than 100 M-1, which is similar to the association constant of calcium with phospholipids.
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35
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Chung L, Kaloyanides G, McDaniel R, McLaughlin A, McLaughlin S. Interaction of gentamicin and spermine with bilayer membranes containing negatively charged phospholipids. Biochemistry 1985; 24:442-52. [PMID: 3978084 DOI: 10.1021/bi00323a030] [Citation(s) in RCA: 104] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
We measured the electrophoretic mobility of multilamellar phospholipid vesicles, the 31P NMR spectra of both sonicated and multilamellar vesicles, and the conductance of planar bilayer membranes to study the binding of spermine and gentamicin to membranes. Spermine and gentamicin do not bind significantly to the zwitterionic lipid phosphatidylcholine. We measured the concentrations of gentamicin and spermine that reverse the charge on vesicles formed from a mixture of phosphatidylcholine and either phosphatidylserine or phosphatidylinositol. From these measurements, we determined that the intrinsic association constants of the cations with these negative lipids are all about 10 M-1. This value is orders of magnitude lower than the apparent binding constants reported in the literature by other groups because the negative electrostatic surface potential of the membranes and the resultant accumulation of these cations in the aqueous diffuse double layer adjacent to the membranes have not been explicitly considered in previous studies. Our main conclusion is that the Gouy-Chapman-Stern theory of the aqueous diffuse double layer can describe surprisingly well the interaction of gentamicin and spermine with bilayer membranes formed in a 0.1 M NaCl solution if the negative phospholipids constitute less than 50% of the membrane. Thus, the theory should be useful for describing the interactions of these cations with the bilayer component of biological membranes, which typically contain less than 50% negative lipids. For example, our results support the suggestion of Sastrasinh et al. [Sastrasinh, M., Krauss, T. C., Weinberg, J. M., & Humes, H. D. (1982) J. Pharmacol. Exp. Ther. 222, 350-358] that phosphatidylinositol is the major binding site for gentamicin in renal brush border membranes.
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37
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Goode DJ, McDaniel R, Plott T, Hiatt J. The effect of legal change on patterns of psychiatric care: the input of change of commitment law. N C Med J 1982; 43:434-8. [PMID: 6955603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Davis JN, Olender E, Maury W, McDaniel R. Alpha-adrenergic regulation of cholinergic responses in rat parotid acinar cells. Mol Pharmacol 1980; 18:356-61. [PMID: 6258046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
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39
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Straus MJ, McDaniel R, Bell E, Reinhard EH. Hereditary hyposplenia in an adult and immunological implications. Case report. Mo Med 1976; 73:78-80, 84. [PMID: 1250213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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