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Ahearne A, Phillips KE, Knehans T, Hoing M, Dowd SE, Stevens DC. Chromosomal organization of biosynthetic gene clusters, including those of nine novel species, suggests plasticity of myxobacterial specialized metabolism. Front Microbiol 2023; 14:1227206. [PMID: 37601375 PMCID: PMC10435759 DOI: 10.3389/fmicb.2023.1227206] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Accepted: 07/11/2023] [Indexed: 08/22/2023] Open
Abstract
Introduction Natural products discovered from bacteria provide critically needed therapeutic leads for drug discovery, and myxobacteria are an established source for metabolites with unique chemical scaffolds and biological activities. Myxobacterial genomes accommodate an exceptional number and variety of biosynthetic gene clusters (BGCs) which encode for features involved in specialized metabolism. Methods In this study, we describe the collection, sequencing, and genome mining of 20 myxobacteria isolated from rhizospheric soil samples collected in North America. Results Nine isolates were determined to be novel species of myxobacteria including representatives from the genera Archangium, Myxococcus, Nannocystis, Polyangium, Pyxidicoccus, Sorangium, and Stigmatella. Growth profiles, biochemical assays, and descriptions were provided for all proposed novel species. We assess the BGC content of all isolates and observe differences between Myxococcia and Polyangiia clusters. Discussion Continued discovery and sequencing of novel myxobacteria from the environment provide BGCs for the genome mining pipeline. Utilizing complete or near-complete genome sequences, we compare the chromosomal organization of BGCs of related myxobacteria from various genera and suggest that the spatial proximity of hybrid, modular clusters contributes to the metabolic adaptability of myxobacteria.
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Affiliation(s)
- Andrew Ahearne
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS, United States
| | - Kayleigh E. Phillips
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS, United States
| | - Thomas Knehans
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS, United States
| | - Miranda Hoing
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS, United States
| | - Scot E. Dowd
- Molecular Research LP (MR DNA), Shallowater, TX, United States
| | - David Cole Stevens
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS, United States
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Ahearne A, Phillips K, Knehans T, Hoing M, Dowd SE, Stevens DC. Chromosomal organization of biosynthetic gene clusters suggests plasticity of myxobacterial specialized metabolism including descriptions for nine novel species: Archangium lansinium sp. nov., Myxococcus landrumus sp. nov., Nannocystis bainbridgea sp. nov., Nannocystis poenicansa sp. nov., Nannocystis radixulma sp. nov., Polyangium mundeleinium sp. nov., Pyxidicoccus parkwaysis sp. nov., Sorangium aterium sp. nov., Stigmatella ashevillena sp. nov. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.08.531766. [PMID: 36945379 PMCID: PMC10028903 DOI: 10.1101/2023.03.08.531766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Natural products discovered from bacteria provide critically needed therapeutic leads for drug discovery, and myxobacteria are an established source for metabolites with unique chemical scaffolds and biological activities. Myxobacterial genomes accommodate an exceptional number and variety of biosynthetic gene clusters (BGCs) which encode for features involved in specialized metabolism. Continued discovery and sequencing of novel myxobacteria from the environment provides BGCs for the genome mining pipeline. Herein, we describe the collection, sequencing, and genome mining of 20 myxobacteria isolated from rhizospheric soil samples collected in North America. Nine isolates where determined to be novel species of myxobacteria including representatives from the genera Archangium, Myxococcus, Nannocystis, Polyangium, Pyxidicoccus, Sorangium, and Stigmatella. Growth profiles, biochemical assays, and descriptions are provided for all proposed novel species. We assess the BGC content of all isolates and observe differences between Myxococcia and Polyangiia clusters. Utilizing complete or near complete genome sequences we compare the chromosomal organization of BGCs of related myxobacteria from various genera and suggest spatial proximity of hybrid, modular clusters contributes to the metabolic adaptability of myxobacteria.
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Affiliation(s)
- Andrew Ahearne
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA
| | - Kayleigh Phillips
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA
| | - Thomas Knehans
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA
| | - Miranda Hoing
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA
| | - Scot E. Dowd
- MR DNA, Molecular Research LP, Shallowater, TX 79363, USA
| | - D. Cole Stevens
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA
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Zeng H, Birkelbach J, Hoffmann J, Popoff A, Volz C, Müller R. Expanding the Ajudazol Cytotoxin Scaffold: Insights from Genome Mining, Biosynthetic Investigations, and Novel Derivatives. JOURNAL OF NATURAL PRODUCTS 2022; 85:2610-2619. [PMID: 36331369 DOI: 10.1021/acs.jnatprod.2c00637] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Myxobacteria have proven to be a rich source of natural products, but their biosynthetic potential seems to be underexplored given the high number of biosynthetic gene clusters present in their genomes. In this study, a truncated ajudazol biosynthetic gene cluster in Cystobacter sp. SBCb004 was identified using mutagenesis and metabolomics analyses and a set of novel ajudazols (named ajudazols C-J, 3-10, respectively) were detected and subsequently isolated. Their structures were elucidated using comprehensive HR-MS and NMR spectroscopy. Unlike the known ajudazols A (1) and B (2), which utilize acetyl-CoA as the biosynthetic starter unit, these novel ajudazols were proposed to incorporate 3,3-dimethylacrylyl CoA as the starter. Ajudazols C-J (3-10, respectively) are characterized by varying degrees of hydroxylation, desaturation, and different glycosylation patterns. Two P450-dependent enzymes and one glycosyltransferase are shown to be responsible for the hydroxylation at C-8, the desaturation at C-15 and C-33, and the transfer of a d-β-glucopyranose, respectively, based on mutagenesis results. One of the cytochrome P450-dependent enzymes and the glycosyltransferase were found to be encoded by genes located outside the biosynthetic gene cluster. Ajudazols C-H (3-8, respectively) exhibit cytotoxicity against various cancer cell lines.
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Affiliation(s)
- Hu Zeng
- Department of Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research and Department of Pharmacy, Saarland University, 66123 Saarbrücken, Saarland, Germany
| | - Joy Birkelbach
- Department of Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research and Department of Pharmacy, Saarland University, 66123 Saarbrücken, Saarland, Germany
| | - Judith Hoffmann
- Department of Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research and Department of Pharmacy, Saarland University, 66123 Saarbrücken, Saarland, Germany
| | - Alexander Popoff
- Department of Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research and Department of Pharmacy, Saarland University, 66123 Saarbrücken, Saarland, Germany
| | - Carsten Volz
- Department of Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research and Department of Pharmacy, Saarland University, 66123 Saarbrücken, Saarland, Germany
| | - Rolf Müller
- Department of Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research and Department of Pharmacy, Saarland University, 66123 Saarbrücken, Saarland, Germany
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Padmanabhan S, Pérez-Castaño R, Osete-Alcaraz L, Polanco MC, Elías-Arnanz M. Vitamin B 12 photoreceptors. VITAMINS AND HORMONES 2022; 119:149-184. [PMID: 35337618 DOI: 10.1016/bs.vh.2022.01.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Photoreceptor proteins enable living organisms to sense light and transduce this signal into biochemical outputs to elicit appropriate cellular responses. Their light sensing is typically mediated by covalently or noncovalently bound molecules called chromophores, which absorb light of specific wavelengths and modulate protein structure and biological activity. Known photoreceptors have been classified into about ten families based on the chromophore and its associated photosensory domain in the protein. One widespread photoreceptor family uses coenzyme B12 or 5'-deoxyadenosylcobalamin, a biological form of vitamin B12, to sense ultraviolet, blue, or green light, and its discovery revealed both a new type of photoreceptor and a novel functional facet of this vitamin, best known as an enzyme cofactor. Large strides have been made in our understanding of how these B12-based photoreceptors function, high-resolution structural descriptions of their functional states are available, as are details of their unusual photochemistry. Additionally, they have inspired notable applications in optogenetics/optobiochemistry and synthetic biology. Here, we provide an overview of what is currently known about these B12-based photoreceptors, their discovery, distribution, molecular mechanism of action, and the structural and photochemical basis of how they orchestrate signal transduction and gene regulation, and how they have been used to engineer optogenetic control of protein activities in living cells.
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Affiliation(s)
- S Padmanabhan
- Instituto de Química Física "Rocasolano", Consejo Superior de Investigaciones Científicas, Madrid, Spain.
| | - Ricardo Pérez-Castaño
- Departamento de Genética y Microbiología, Área de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia, Spain
| | - Lucía Osete-Alcaraz
- Departamento de Genética y Microbiología, Área de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia, Spain
| | - María Carmen Polanco
- Departamento de Genética y Microbiología, Área de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia, Spain
| | - Montserrat Elías-Arnanz
- Departamento de Genética y Microbiología, Área de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia, Spain.
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Zhao Y, Wang Y, Xia C, Li X, Ye X, Fan Q, Huang Y, Li Z, Zhu C, Cui Z. Whole-Genome Sequencing of Corallococcus sp. Strain EGB Reveals the Genetic Determinants Linking Taxonomy and Predatory Behavior. Genes (Basel) 2021; 12:genes12091421. [PMID: 34573403 PMCID: PMC8466578 DOI: 10.3390/genes12091421] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Revised: 09/13/2021] [Accepted: 09/13/2021] [Indexed: 11/16/2022] Open
Abstract
Corallococcus sp. strain EGB is a Gram-negative myxobacteria isolated from saline soil, and has considerable potential for the biocontrol of phytopathogenic fungi. However, the detailed mechanisms related to development and predatory behavior are unclear. To obtain a comprehensive overview of genetic features, the genome of strain EGB was sequenced, annotated, and compared with 10 other Corallococcus species. The strain EGB genome was assembled as a single circular chromosome of 9.4 Mb with 7916 coding genes. Phylogenomics analysis showed that strain EGB was most closely related to Corallococcus interemptor AB047A, and it was inferred to be a novel species within the Corallococcus genus. Comparative genomic analysis revealed that the pan-genome of Corallococcus genus was large and open. Only a small proportion of genes were specific to strain EGB, and most of them were annotated as hypothetical proteins. Subsequent analyses showed that strain EGB produced abundant extracellular enzymes such as chitinases and β-(1,3)-glucanases, and proteases to degrade the cell-wall components of phytopathogenic fungi. In addition, 35 biosynthetic gene clusters potentially coding for antimicrobial compounds were identified in the strain EGB, and the majority of them were present in the dispensable pan-genome with unexplored metabolites. Other genes related to secretion and regulation were also explored for strain EGB. This study opens new perspectives in the greater understanding of the predatory behavior of strain EGB, and facilitates a potential application in the biocontrol of fungal plant diseases in the future.
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Affiliation(s)
- Yuqiang Zhao
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
- Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China
| | - Yanxin Wang
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Chengyao Xia
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Xu Li
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Xianfeng Ye
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Qiwen Fan
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Yan Huang
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Zhoukun Li
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Cancan Zhu
- Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China
| | - Zhongli Cui
- Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
- Key Laboratory of Plant Immunity, Nanjing Agricultural University, Nanjing 210095, China
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Ahearne A, Albataineh H, Dowd SE, Stevens DC. Assessment of Evolutionary Relationships for Prioritization of Myxobacteria for Natural Product Discovery. Microorganisms 2021; 9:microorganisms9071376. [PMID: 34202719 PMCID: PMC8307915 DOI: 10.3390/microorganisms9071376] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 06/03/2021] [Accepted: 06/21/2021] [Indexed: 02/06/2023] Open
Abstract
Discoveries of novel myxobacteria have started to unveil the potentially vast phylogenetic diversity within the family Myxococcaceae and have brought about an updated approach to myxobacterial classification. While traditional approaches focused on morphology, 16S gene sequences, and biochemistry, modern methods including comparative genomics have provided a more thorough assessment of myxobacterial taxonomy. Herein, we utilize long-read genome sequencing for two myxobacteria previously classified as Archangium primigenium and Chondrococcus macrosporus, as well as four environmental myxobacteria newly isolated for this study. Average nucleotide identity and digital DNA-DNA hybridization scores from comparative genomics suggest previously classified as A. primigenium to instead be a novel member of the genus Melittangium, C. macrosporus to be a potentially novel member of the genus Corallococcus with high similarity to Corallococcus exercitus, and the four isolated myxobacteria to include another novel Corallococcus species, a novel Pyxidicoccus species, a strain of Corallococcus exiguus, and a potentially novel Myxococcus species with high similarity to Myxococcus stipitatus. We assess the biosynthetic potential of each sequenced myxobacterium and suggest that genus-level conservation of biosynthetic pathways support our preliminary taxonomic assignment. Altogether, we suggest that long-read genome sequencing benefits the classification of myxobacteria and improves determination of biosynthetic potential for prioritization of natural product discovery.
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Affiliation(s)
- Andrew Ahearne
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA; (A.A.); (H.A.)
| | - Hanan Albataineh
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA; (A.A.); (H.A.)
| | - Scot E. Dowd
- MR DNA, Molecular Research LP, Shallowater, TX 79363, USA;
| | - D. Cole Stevens
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA; (A.A.); (H.A.)
- Correspondence: ; Tel.: +1-662-915-5730
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Light-Triggered Carotenogenesis in Myxococcus xanthus: New Paradigms in Photosensory Signaling, Transduction and Gene Regulation. Microorganisms 2021; 9:microorganisms9051067. [PMID: 34063365 PMCID: PMC8156234 DOI: 10.3390/microorganisms9051067] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 05/11/2021] [Accepted: 05/12/2021] [Indexed: 11/17/2022] Open
Abstract
Myxobacteria are Gram-negative δ-proteobacteria found predominantly in terrestrial habitats and often brightly colored due to the biosynthesis of carotenoids. Carotenoids are lipophilic isoprenoid pigments that protect cells from damage and death by quenching highly reactive and toxic oxidative species, like singlet oxygen, generated upon growth under light. The model myxobacterium Myxococcus xanthus turns from yellow in the dark to red upon exposure to light because of the photoinduction of carotenoid biosynthesis. How light is sensed and transduced to bring about regulated carotenogenesis in order to combat photooxidative stress has been extensively investigated in M. xanthus using genetic, biochemical and high-resolution structural methods. These studies have unearthed new paradigms in bacterial light sensing, signal transduction and gene regulation, and have led to the discovery of prototypical members of widely distributed protein families with novel functions. Major advances have been made over the last decade in elucidating the molecular mechanisms underlying the light-dependent signaling and regulation of the transcriptional response leading to carotenogenesis in M. xanthus. This review aims to provide an up-to-date overview of these findings and their significance.
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2-Hydroxysorangiadenosine: Structure and Biosynthesis of a Myxobacterial Sesquiterpene-Nucleoside. Molecules 2020; 25:molecules25112676. [PMID: 32527018 PMCID: PMC7321100 DOI: 10.3390/molecules25112676] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 06/05/2020] [Accepted: 06/05/2020] [Indexed: 12/02/2022] Open
Abstract
Myxobacteria represent an under-investigated source for biologically active natural products featuring intriguing structural moieties with potential applications, e.g., in the pharmaceutical industry. Sorangiadenosine and the here-discovered 2-hydroxysorangiadenosine are myxobacterial sesquiterpene–nucleosides with an unusual structural moiety, a bicyclic eudesmane-type sesquiterpene. As the biosynthesis of these rare terpene–nucleoside hybrid natural products remains elusive, we investigated secondary metabolomes and genomes of several 2-hydroxysorangiadenosine-producing myxobacteria. We report the isolation and full structure elucidation of 2-hydroxysorangiadenosine and its cytotoxic and antibiotic activities and propose a biosynthetic pathway in the myxobacterium Vitiosangium cumulatum MCy10943T.
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Mo XH, Zhang H, Wang TM, Zhang C, Zhang C, Xing XH, Yang S. Establishment of CRISPR interference in Methylorubrum extorquens and application of rapidly mining a new phytoene desaturase involved in carotenoid biosynthesis. Appl Microbiol Biotechnol 2020; 104:4515-4532. [PMID: 32215707 DOI: 10.1007/s00253-020-10543-w] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 03/02/2020] [Accepted: 03/11/2020] [Indexed: 02/04/2023]
Abstract
The methylotrophic bacterium Methylorubrum extorquens AM1 holds a great potential of a microbial cell factory in producing high value chemicals with methanol as the sole carbon and energy source. However, many gene functions remain unknown, hampering further rewiring of metabolic networks. Clustered regularly interspaced short palindromic repeat interference (CRISPRi) has been demonstrated to be a robust tool for gene knockdown in diverse organisms. In this study, we developed an efficient CRISPRi system through optimizing the promoter strength of Streptococcus pyogenes-derived deactivated cas9 (dcas9). When the dcas9 and sgRNA were respectively controlled by medium PR/tetO and strong PmxaF-g promoters, dynamic repression efficacy of cell growth through disturbing a central metabolism gene glyA was achieved from 41.9 to 96.6% dependent on the sgRNA targeting sites. Furthermore, the optimized CRISPRi system was shown to effectively decrease the abundance of exogenous fluorescent protein gene mCherry over 50% and to reduce the expression of phytoene desaturase gene crtI by 97.7%. We then used CRISPRi technology combined with 26 sgRNAs pool to rapidly discover a new phytoene desaturase gene META1_3670 from 2470 recombinant mutants. The gene function was further verified through gene deletion and complementation as well as phylogenetic tree analysis. In addition, we applied CRISPRi to repress the transcriptional level of squalene-hopene cyclase gene shc involved in hopanoid biosynthesis by 64.9%, which resulted in enhancing 1.9-fold higher of carotenoid production without defective cell growth. Thus, the CRISPRi system developed here provides a useful tool in mining functional gene of M. extorquens as well as in biotechnology for producing high-valued chemicals from methanol. KEY POINTS: Developing an efficient CRISPRi to knockdown gene expression in C1-utilizing bacteria CRISPRi combined with sgRNAs pool to rapidly discover a new phytoene desaturase gene Improvement of carotenoid production by repressing a competitive pathway.
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Affiliation(s)
- Xu-Hua Mo
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Hui Zhang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Tian-Min Wang
- Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China
| | - Chong Zhang
- Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China
| | - Cong Zhang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Xin-Hui Xing
- Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China
| | - Song Yang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China.
- Key Laboratory of Systems Bioengineering, Ministry of Education, Tianjin University, Tianjin, People's Republic of China.
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Pérez J, Muñoz-Dorado J, Moraleda-Muñoz A. The complex global response to copper in the multicellular bacterium Myxococcus xanthus. Metallomics 2019; 10:876-886. [PMID: 29961779 DOI: 10.1039/c8mt00121a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The complex copper response of the multicellular proteobacterium M. xanthus includes structural genes similar to those described in other bacteria, such as P1B-type ATPases, multicopper oxidases, and heavy metal efflux systems. However, the two time-dependent expression profiles of the different copper systems are unique. There are a number of genes responsible for an immediate response, whose expression increases after the addition of copper, but rapidly decreases thereafter to basal levels. The regulatory element that controls this early response is CorE, a novel extracytoplasmic function σ factor that is activated by Cu2+ and inactivated by Cu+. Other genes are part of a maintenance response. These genes show a profile that slows up after the copper addition and reaches a plateau at 24-48 h incubation. Most of the genes involved in this response are encoded by the operon curA, which is regulated by the two-component system CorSR. Moreover, other genes involved in the maintenance response are regulated by different regulatory elements that remain unknown. Additionally, copper activates the transcription of the structural genes for carotenoid synthesis through a mechanism that requires the activation of the σ factor CarQ. Bearing in mind that M. xanthus is not very resistant to copper, it is speculated that the complexity of its copper response might be related to its complex life cycle.
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Affiliation(s)
- Juana Pérez
- Departamento de Microbiología, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain.
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Gregory K, Salvador LA, Akbar S, Adaikpoh BI, Stevens DC. Survey of Biosynthetic Gene Clusters from Sequenced Myxobacteria Reveals Unexplored Biosynthetic Potential. Microorganisms 2019; 7:E181. [PMID: 31238501 PMCID: PMC6616573 DOI: 10.3390/microorganisms7060181] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 06/20/2019] [Accepted: 06/21/2019] [Indexed: 01/31/2023] Open
Abstract
Coinciding with the increase in sequenced bacteria, mining of bacterial genomes for biosynthetic gene clusters (BGCs) has become a critical component of natural product discovery. The order Myxococcales, a reputable source of biologically active secondary metabolites, spans three suborders which all include natural product producing representatives. Utilizing the BiG-SCAPE-CORASON platform to generate a sequence similarity network that contains 994 BGCs from 36 sequenced myxobacteria deposited in the antiSMASH database, a total of 843 BGCs with lower than 75% similarity scores to characterized clusters within the MIBiG database are presented. This survey provides the biosynthetic diversity of these BGCs and an assessment of the predicted chemical space yet to be discovered. Considering the mere snapshot of myxobacteria included in this analysis, these untapped BGCs exemplify the potential for natural product discovery from myxobacteria.
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Affiliation(s)
- Katherine Gregory
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
| | - Laura A Salvador
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
| | - Shukria Akbar
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
| | - Barbara I Adaikpoh
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
| | - D Cole Stevens
- Department of BioMolecular Sciences, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
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12
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Pick U, Zarka A, Boussiba S, Davidi L. A hypothesis about the origin of carotenoid lipid droplets in the green algae Dunaliella and Haematococcus. PLANTA 2019; 249:31-47. [PMID: 30470898 DOI: 10.1007/s00425-018-3050-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Accepted: 11/14/2018] [Indexed: 05/20/2023]
Abstract
Hypercarotenogenesis in green algae evolved by mutation of PSY that increased its transcription at high light, disintegration of the eyespot in Dunaliella and acquisition of the capacity to export carotenoids from chloroplasts in Haematococcus. Carotenoids (Car) are lipid-soluble pigments synthesized in plants, algae, bacteria and fungi. Car have strong antioxidative properties and as such are utilized to reduce the danger of different diseases in humans. Two green microalgae are utilized as rich natural sources for Car: Dunaliella salina/bardawil accumulates 10% (w/w) β-carotene (βC), which is also pro-vitamin A, and Haematococcus pluvialis accumulates 4% (w/w) astaxanthin (Ast), the strongest antioxidant among Car. D. bardawil accumulates βC in plastoglobules within the chloroplast, whereas H. pluvialis deposits Ast in cytoplasmic lipid droplets (CLD). In this review we compare the hypercarotenogenic responses (HCR) in Dunaliella and in Haematococcus and try to outline hypothetical evolutionary pathways for its origin. We propose that a mutation in phytoene synthetase that increased its transcription level in response to high light stress had a pivotal role in the evolution of the HCR. Proteomic analyses indicated that in D. bardawil/salina the HCR evolved from dissociation and amplification of eyespot lipid globules. The more robust HCR in algae that accumulate carotenoids in CLD, such as H. pluvialis, required also acquisition of the capacity to export βC out of the chloroplast and its enzymatic conversion into Ast.
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Affiliation(s)
- Uri Pick
- Department of Biomolecular Sciences, The Weizmann Institute of Science, 76100, Rehovot, Israel.
| | - Aliza Zarka
- Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boker Campus, Beer-Sheva, 8499000, Israel
| | - Sammy Boussiba
- Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boker Campus, Beer-Sheva, 8499000, Israel
| | - Lital Davidi
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, 90095-1569, USA
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Padmanabhan S, Jost M, Drennan CL, Elías-Arnanz M. A New Facet of Vitamin B 12: Gene Regulation by Cobalamin-Based Photoreceptors. Annu Rev Biochem 2017; 86:485-514. [PMID: 28654327 PMCID: PMC7153952 DOI: 10.1146/annurev-biochem-061516-044500] [Citation(s) in RCA: 79] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Living organisms sense and respond to light, a crucial environmental factor, using photoreceptors, which rely on bound chromophores such as retinal, flavins, or linear tetrapyrroles for light sensing. The discovery of photoreceptors that sense light using 5'-deoxyadenosylcobalamin, a form of vitamin B12 that is best known as an enzyme cofactor, has expanded the number of known photoreceptor families and unveiled a new biological role of this vitamin. The prototype of these B12-dependent photoreceptors, the transcriptional repressor CarH, is widespread in bacteria and mediates light-dependent gene regulation in a photoprotective cellular response. CarH activity as a transcription factor relies on the modulation of its oligomeric state by 5'-deoxyadenosylcobalamin and light. This review surveys current knowledge about these B12-dependent photoreceptors, their distribution and mode of action, and the structural and photochemical basis of how they orchestrate signal transduction and control gene expression.
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Affiliation(s)
- S Padmanabhan
- Instituto de Química Física Rocasolano, Consejo Superior de Investigaciones Científicas, 28006 Madrid, Spain;
| | - Marco Jost
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94158-2140;
| | - Catherine L Drennan
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
- Department of Biology and Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139;
| | - Montserrat Elías-Arnanz
- Departamento de Genética y Microbiología, Área de Genética, Unidad Asociada al Instituto de Química Física Rocasolano, Consejo Superior de Investigaciones Científicas, Facultad de Biología, Universidad de Murcia, 30100 Murcia, Spain;
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Hiseni A, Arends IWCE, Otten LG. New Cofactor-Independent Hydration Biocatalysts: Structural, Biochemical, and Biocatalytic Characteristics of Carotenoid and Oleate Hydratases. ChemCatChem 2014. [DOI: 10.1002/cctc.201402511] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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Hoffmann J, Bóna-Lovász J, Beuttler H, Altenbuchner J. In vivo and in vitro studies on the carotenoid cleavage oxygenases from Sphingopyxis alaskensis RB2256 and Plesiocystis pacifica SIR-1 revealed their substrate specificities and non-retinal-forming cleavage activities. FEBS J 2012; 279:3911-24. [PMID: 22901074 DOI: 10.1111/j.1742-4658.2012.08751.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Revised: 07/25/2012] [Accepted: 08/07/2012] [Indexed: 01/17/2023]
Abstract
Carotenoid cleavage oxygenases are nonheme iron enzymes that specifically cleave carbon-carbon double bonds of carotenoids. Their apocarotenoid cleavage products serve as important signaling molecules that are involved in various biological processes. A database search revealed the presence of putative carotenoid cleavage oxygenase genes in the genomes of Sphingopyxis alaskensis RB2256 and Plesiocystis pacifica SIR-1. The four genes sala_1698, sala_1008, ppsir1_15490 and ppsir1_17230 were cloned and heterologously expressed in carotenoid-producing Escherichia coli JM109 strains. Two of the four encoded proteins exhibited carotenoid cleavage activity. S. alaskensis RB2256 carotenoid cleavage oxygenase (SaCCO), which is encoded by sala_1698, was shown to cleave acyclic and monocyclic substrates. Coexpression of sala_1698 in carotenoid-producing E. coli JM109 strains revealed cleavage activity for lycopene, hydroxylycopene, and dihydroxylycopene. The monocyclic substrate apo-8'-carotenal was cleaved in vitro by purified SaCCO at the 9'/10' and 11'/12' double bonds. The second enzyme, P. pacifica SIR-1 carotenoid cleavage oxygenase (PpCCO), is encoded by ppsir1_15490. PpCCO-mediated carotenoid cleavage requires the presence of either hydroxy or keto groups. PpCCO cleaved zeaxanthin, hydroxylycopene, and dihydroxylycopene, and also the C(50) carotenoids decaprenoxanthin, sarprenoxanthin and sarcinaxanthin, in carotenoid-producing E. coli JM109 strains. Whole cells of E. coli JM109 overexpressing ppsir1_15490mut, a mutant of ppsir1_15490 with enhanced gene expression, were applied for the conversion of carotenoids. Analysis of the carotenoid cleavage products revealed a single cleavage site at the 13'/14' double bond for astaxanthin, and two cleavage sites at the 11'/12' or 13'/14' double bond for zeaxanthin, nostoxanthin, and canthaxanthin.
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Affiliation(s)
- Jana Hoffmann
- Institute of Industrial Genetics, University of Stuttgart, Stuttgart, Germany
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Hiseni A, Arends IWCE, Otten LG. Biochemical characterization of the carotenoid 1,2-hydratases (CrtC) from Rubrivivax gelatinosus and Thiocapsa roseopersicina. Appl Microbiol Biotechnol 2011; 91:1029-36. [PMID: 21590288 PMCID: PMC3145076 DOI: 10.1007/s00253-011-3324-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2011] [Revised: 04/03/2011] [Accepted: 04/09/2011] [Indexed: 11/28/2022]
Abstract
Two carotenoid 1,2-hydratase (CrtC) genes from the photosynthetic bacteria Rubrivivax gelatinosus and Thiocapsa roseopersicina were cloned and expressed in Escherichia coli in an active form and purified by affinity chromatography. The biochemical properties of the recombinant enzymes and their substrate specificities were studied. The purified CrtCs catalyze cofactor independently the conversion of lycopene to 1-HO- and 1,1′-(HO)2-lycopene. The optimal pH and temperature for hydratase activity was 8.0 and 30°C, respectively. The apparent Km and Vmax values obtained for the hydration of lycopene were 24 μM and 0.31 nmol h−1 mg−1 for RgCrtC and 9.5 μM and 0.15 nmol h−1 mg−1 for TrCrtC, respectively. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis revealed two protein bands of 44 and 38 kDa for TrCrtC, which indicate protein processing. Both hydratases are also able to convert the unnatural substrate geranylgeraniol (C20 substrate), which functionally resembles the natural substrate lycopene.
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Affiliation(s)
- Aida Hiseni
- Biocatalysis and Organic Chemistry, Department of Biotechnology, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
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Elías-Arnanz M, Padmanabhan S, Murillo FJ. The regulatory action of the myxobacterial CarD/CarG complex: a bacterial enhanceosome? FEMS Microbiol Rev 2010; 34:764-78. [PMID: 20561058 DOI: 10.1111/j.1574-6976.2010.00235.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
A global regulatory complex made up of two unconventional transcriptional factors, CarD and CarG, is implicated in the control of various processes in Myxococcus xanthus, a Gram-negative bacterium that serves as a prokaryotic model system for multicellular development and the response to blue light. CarD has a unique two-domain architecture composed of: (1) a C-terminal DNA-binding domain that resembles eukaryotic high mobility group A (HMGA) proteins, which are relatively abundant, nonhistone components of chromatin that remodel DNA and prime it for the assembly of multiprotein-DNA complexes essential for various DNA transactions, and (2) an N-terminal domain involved in interactions with CarG and RNA polymerase, which is also the founding member of the large CarD_TRCF family of bacterial proteins. CarG, which does not bind DNA directly, has a zinc-binding motif of the type found in the archaemetzincin class of metalloproteases that, in CarG, appears to play a purely structural role. This review aims to provide an overview of the known molecular details and insights emerging from the study of the singular CarD-CarG prokaryotic regulatory complex and its parallels with enhanceosomes, the higher order, nucleoprotein transcription complexes in eukaryotes.
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Affiliation(s)
- Montserrat Elías-Arnanz
- Departamento de Genética y Microbiología, Area de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia, Spain
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Sun Z, Shen S, Wang C, Wang H, Hu Y, Jiao J, Ma T, Tian B, Hua Y. A novel carotenoid 1,2-hydratase (CruF) from two species of the non-photosynthetic bacterium Deinococcus. MICROBIOLOGY-SGM 2009; 155:2775-2783. [PMID: 19443548 DOI: 10.1099/mic.0.027623-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A novel carotenoid 1,2-hydratase (CruF) responsible for the C-1',2' hydration of gamma-carotene was identified in the non-photosynthetic bacteria Deinococcus radiodurans R1 and Deinococcus geothermalis DSM 11300. Gene expression and disruption experiments demonstrated that dr0091 and dgeo2309 encode CruF in D. radiodurans and D. geothermalis, respectively. Their homologues were also found in the genomes of cyanobacteria, and exhibited little homology to the hydroxyneurosporene synthase (CrtC) proteins found mainly in photosynthetic bacteria. Phylogenetic analysis showed that CruF homologues form a separate family, which is evolutionarily distant from the known CrtC family.
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Affiliation(s)
- Zongtao Sun
- Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
| | - Shaochuan Shen
- State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology, College of Chemical Engineering and Materials Science, Zhejiang University of Technology, 310032 Hangzhou, China.,Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
| | - Chao Wang
- Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
| | - Hu Wang
- Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
| | - Yaping Hu
- Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
| | - Jiandong Jiao
- Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
| | - Tingting Ma
- Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
| | - Bing Tian
- Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
| | - Yuejin Hua
- Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, China
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Iniesta AA, Cervantes M, Murillo FJ. Conversion of the lycopene monocyclase of Myxococcus xanthus into a bicyclase. Appl Microbiol Biotechnol 2008; 79:793-802. [DOI: 10.1007/s00253-008-1481-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2008] [Revised: 03/10/2008] [Accepted: 03/28/2008] [Indexed: 10/22/2022]
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20
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Galbis-Martínez L, Galbis-Martínez M, Murillo FJ, Fontes M. An anti-antisigma factor in the response of the bacterium Myxococcus xanthus to blue light. MICROBIOLOGY-SGM 2008; 154:895-904. [PMID: 18310035 DOI: 10.1099/mic.0.2007/013359-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Cells of the Gram-negative bacterium Myxococcus xanthus respond to blue light by producing carotenoids, pigments that play a protective role against the oxidative effects of light. Blue light triggers a network of regulatory actions that lead to the transcriptional activation of the structural genes for carotenoid synthesis. The product of carF, similar to a family of proteins of unknown function called Kua, is an early regulator of this process. Previous genetic data indicate that CarF participates in the light-dependent inactivation of the antisigma factor CarR. In the dark, CarR sequesters the ECF-sigma factor CarQ to the membrane, thereby preventing the activation of the structural genes for carotenoid synthesis. Using a bacterial two-hybrid system, we show here that both CarF and CarQ physically interact with CarR. These results, together with the finding that CarF is located at the membrane, support the hypothesis that CarF acts as an anti-antisigma factor. Comparison of CarF with other Kua proteins shows a remarkable conservation of a number of histidine residues. The effects on CarF function of several histidine to alanine substitutions and of the truncation of specific CarF domains are also reported here.
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Affiliation(s)
- Lilian Galbis-Martínez
- Departamento de Genética y Microbiología (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, 30100 Murcia, Spain
| | - Marisa Galbis-Martínez
- Departamento de Genética y Microbiología (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, 30100 Murcia, Spain
| | - Francisco J Murillo
- Departamento de Genética y Microbiología (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, 30100 Murcia, Spain
| | - Marta Fontes
- Departamento de Genética y Microbiología (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, 30100 Murcia, Spain
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Pérez-Marín MC, Padmanabhan S, Polanco MC, Murillo FJ, Elías-Arnanz M. Vitamin B12 partners the CarH repressor to downregulate a photoinducible promoter in Myxococcus xanthus. Mol Microbiol 2008; 67:804-19. [PMID: 18315685 DOI: 10.1111/j.1365-2958.2007.06086.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A light-inducible promoter, P(B), drives expression of the carB operon in Myxococcus xanthus. Repressed by CarA in the dark, P(B) is activated when CarS, produced in the light, sequesters CarA to prevent operator-CarA binding. The MerR-type, N-terminal domain of CarA, which mediates interactions with both operator and CarS, is linked to a C-terminal oligomerization module with a predicted cobalamin-binding motif. Here, we show that although CarA does bind vitamin B12, mutating the motif involved has no effect on its ability to repress P(B). Intriguingly, P(B) could be repressed in the dark even with no CarA, so long as B12 and an intact CarA operator were present. We have discovered that this effect of B12 depends on the gene immediately downstream of carA. Its product, CarH, also consists of a MerR-type, N-terminal domain that specifically recognizes the CarA operator and CarS, linked to a predicted B12-binding C-terminal oligomerization module. The B12-mediated repression of P(B) in the dark is relieved by deleting carH, by mutating the DNA- or B12-binding residues of CarH, or by illumination. Our findings unveil parallel regulatory circuits that control a light-inducible promoter using a transcriptional factor repertoire that includes a paralogous gene pair and vitamin B12.
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Affiliation(s)
- Mari Cruz Pérez-Marín
- Departamento de Genética y Microbiología, Area de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia 30100, Spain
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22
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Iniesta AA, Cervantes M, Murillo FJ. Cooperation of two carotene desaturases in the production of lycopene in Myxococcus xanthus. FEBS J 2007; 274:4306-14. [PMID: 17662111 DOI: 10.1111/j.1742-4658.2007.05960.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In Myxococcus xanthus, all known carotenogenic genes are grouped together in the gene cluster carB-carA, except for one, crtIb (previously named carC). We show here that the first three genes of the carB operon, crtE, crtIa, and crtB, encode a geranygeranyl synthase, a phytoene desaturase, and a phytoene synthase, respectively. We demonstrate also that CrtIa possesses cis-to-trans isomerase activity, and is able to dehydrogenate phytoene, producing phytofluene and zeta-carotene. Unlike the majority of CrtI-type phytoene desaturases, CrtIa is unable to perform the four dehydrogenation events involved in converting phytoene to lycopene. CrtIb, on the other hand, is incapable of dehydrogenating phytoene and lacks cis-to-trans isomerase activity. However, the presence of both CrtIa and CrtIb allows the completion of the four desaturation steps that convert phytoene to lycopene. Therefore, we report a unique mechanism where two distinct CrtI-type desaturases cooperate to carry out the four desaturation steps required for lycopene formation. In addition, we show that there is a difference in substrate recognition between the two desaturases; CrtIa dehydrogenates carotenes in the cis conformation, whereas CrtIb dehydrogenates carotenes in the trans conformation.
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Affiliation(s)
- Antonio A Iniesta
- Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, Spain.
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Navarro-Avilés G, Jiménez MA, Pérez-Marín MC, González C, Rico M, Murillo FJ, Elías-Arnanz M, Padmanabhan S. Structural basis for operator and antirepressor recognition by Myxococcus xanthus CarA repressor. Mol Microbiol 2007; 63:980-94. [PMID: 17233828 DOI: 10.1111/j.1365-2958.2006.05567.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Blue light induces carotenogenesis in Myxococcus xanthus. The carB operon encodes all but one of the structural genes involved, and its expression is regulated by the CarA-CarS repressor-antirepressor pair. In the dark, CarA-operator binding represses carB. CarS, produced on illumination, interacts physically with CarA to dismantle the CarA-operator complex and activate carB. Both operator and CarS bind to the autonomously folded N-terminal domain of CarA, CarA(Nter), which in excess represses carB. Here, we report the NMR structure of CarA(Nter), and map residues that interact with operator and CarS by NMR chemical shift perturbations, and in vivo and in vitro analyses of site-directed mutants. We show CarA(Nter) adopts the winged-helix topology of MerR-family DNA-binding domains, and conserves the majority of the helix-turn-helix and wing contacts with DNA. Tellingly, helix alpha2 in CarA, a key element in operator DNA recognition, is also critical for interaction with CarS, implying that the CarA-CarS protein-protein and the CarA-operator protein-DNA interfaces overlap. Thus, binding of CarA to operator and to antirepressor are mutually exclusive, and CarA may discern structural features in the acidic CarS protein that resemble operator DNA. Repressor inactivation by occluding the DNA-binding region may be a recurrent mechanism of action for acidic antirepressors.
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Affiliation(s)
- Gloria Navarro-Avilés
- Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, Murcia, Spain
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Maresca JA, Bryant DA. Two genes encoding new carotenoid-modifying enzymes in the green sulfur bacterium Chlorobium tepidum. J Bacteriol 2006; 188:6217-23. [PMID: 16923888 PMCID: PMC1595356 DOI: 10.1128/jb.00766-06] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The green sulfur bacterium Chlorobium tepidum produces chlorobactene as its primary carotenoid. Small amounts of chlorobactene are hydroxylated by the enzyme CrtC and then glucosylated and acylated to produce chlorobactene glucoside laurate. The genes encoding the enzymes responsible for these modifications of chlorobactene, CT1987, and CT0967, have been identified by comparative genomics, and these genes were insertionally inactivated in C. tepidum to verify their predicted function. The gene encoding chlorobactene glucosyltransferase (CT1987) has been named cruC, and the gene encoding chlorobactene lauroyltransferase (CT0967) has been named cruD. Homologs of these genes are found in the genomes of all sequenced green sulfur bacteria and filamentous anoxygenic phototrophs as well as in the genomes of several nonphotosynthetic bacteria that produce similarly modified carotenoids. The other bacteria in which these genes are found are not closely related to green sulfur bacteria or to one another. This suggests that the ability to synthesize modified carotenoids has been a frequently transferred trait.
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Affiliation(s)
- Julia A Maresca
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, S-235 Frear Building, PA 16802, USA
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Duc LH, Fraser PD, Tam NKM, Cutting SM. Carotenoids present in halotolerantBacillusspore formers. FEMS Microbiol Lett 2006; 255:215-24. [PMID: 16448498 DOI: 10.1111/j.1574-6968.2005.00091.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Six isolates of pigmented spore-forming bacteria were recovered from human faeces from subjects in Vietnam. 16S rRNA analysis demonstrated close association with known pigmented Bacillus species. All isolates were able to tolerate growth on 8% NaCl and were resistant to arsenate, characteristics that make them most related to Bacillus indicus. Two visible pigments were apparent, a yellow pigment found in vegetative cells and an orange pigment found only in spores. We used high-performance liquid chromatography to characterize and quantify these pigments and found them to be carotenoids. The biosynthetic pathway that generates them branches with one that could lead to the spore-associated orange pigmentation. Although these bacteria were found in faeces, the seafood-rich diet of Vietnam and the recovery of other pigmented Bacillus species from seafood and marine environments makes it highly probable that the true origin of these bacteria is from ingested seafood.
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Affiliation(s)
- Le H Duc
- School of Biological Sciences, Royal Holloway University of London, Egham, Surrey, UK
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Pelz A, Wieland KP, Putzbach K, Hentschel P, Albert K, Götz F. Structure and biosynthesis of staphyloxanthin from Staphylococcus aureus. J Biol Chem 2005; 280:32493-8. [PMID: 16020541 DOI: 10.1074/jbc.m505070200] [Citation(s) in RCA: 246] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Most Staphylococcus aureus strains produce the orange carotenoid staphyloxanthin. The staphyloxanthin biosynthesis genes are organized in an operon, crtOPQMN, with a sigma(B)-dependent promoter upstream of crtO and a termination region downstream of crtN. The functions of the five encoded enzymes were predicted on the basis of their sequence similarity to known enzymes and by product analysis of gene deletion mutants. The first step in staphyloxanthin biosynthesis is the head-to-head condensation of two molecules of farnesyl diphosphate to form dehydrosqualene (4,4'-diapophytoene), catalyzed by the dehydrosqualene synthase CrtM. The dehydrosqualene desaturase CrtN dehydrogenates dehydrosqualene to form the yellow, main intermediate 4,4'-diaponeurosporene. CrtP, very likely a mixed function oxidase, oxidizes the terminal methyl group of 4,4'-diaponeurosporene to form 4,4'-diaponeurosporenic acid. CrtQ, a glycosyltransferase, esterifies glucose at the C(1)'' position with the carboxyl group of 4,4'-diaponeurosporenic acid to yield glycosyl 4,4'-diaponeurosporenoate; this compound was the major product in the clone expressing crtPQMN. In the final step, the acyltransferase CrtO esterifies glucose at the C(6)'' position with the carboxyl group of 12-methyltetradecanoic acid to yield staphyloxanthin. Staphyloxanthin overexpressed in Staphylococcus carnosus (pTX-crtOPQMN) and purified was analyzed by high pressure liquid chromatography-mass spectroscopy and NMR spectroscopy. Staphyloxanthin was identified as beta-D-glucopyranosyl 1-O-(4,4'-diaponeurosporen-4-oate)-6-O-(12-methyltetradecanoate).
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Affiliation(s)
- Alexandra Pelz
- Department of Microbial Genetics, University of Tuebingen, Germany
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27
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Moraleda-Muñoz A, Pérez J, Fontes M, Murillo FJ, Muñoz-Dorado J. Copper induction of carotenoid synthesis in the bacterium Myxococcus xanthus. Mol Microbiol 2005; 56:1159-68. [PMID: 15882411 DOI: 10.1111/j.1365-2958.2005.04613.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Copper induces a red pigmentation in cells of the bacterium Myxococcus xanthus when they are incubated in the dark, at suboptimal growth conditions. The colouration results from the accumulation of carotenoids, as demonstrated by chemical analysis, and by the lack of a copper effect on M. xanthus mutants affected in known structural genes for carotenoid synthesis. None of several other metals or oxidative agents can mimic the copper effect on carotenoid synthesis. Until now, blue light was the only environmental agent known to induce carotenogenesis in M. xanthus. As happens for the blue light, copper activates the transcription of the structural genes for carotenoid synthesis through the transcriptional activation of the carQRS operon. This encodes the ECF sigma factor CarQ, directly or indirectly responsible for the activation of the structural genes, and the anti-sigma factor CarR, which physically interacts with CarQ to blocks its action in the absence of external stimuli. All but one of the other regulatory elements known to participate in the induction of carotenoid synthesis by blue light are required for the response to copper. The exception is CarF, a protein required for the light-mediated dismantling of the CarR-CarQ complex. In addition to carotenogenesis, copper induces other unknown cellular mechanisms that confer tolerance to the metal.
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Affiliation(s)
- Aurelio Moraleda-Muñoz
- Departamento de Microbiología, Instituto de Biotecnología, Facultad de Ciencias, Universidad de Granada, Avda, Fuentenueva s/n, E-18071 Granada, Spain
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28
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Takano H, Obitsu S, Beppu T, Ueda K. Light-induced carotenogenesis in Streptomyces coelicolor A3(2): identification of an extracytoplasmic function sigma factor that directs photodependent transcription of the carotenoid biosynthesis gene cluster. J Bacteriol 2005; 187:1825-32. [PMID: 15716454 PMCID: PMC1064024 DOI: 10.1128/jb.187.5.1825-1832.2005] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Carotenoids are produced by a variety of organisms, but the mechanisms that regulate gene expression leading to carotenoid biosynthesis have been characterized for only a few organisms. In this study, we found that Streptomyces coelicolor A3(2), a gram-positive filamentous bacterium, produces carotenoids under blue light induction. The carotenoid fraction isolated from the cell extract contained multiple compounds, including isorenieratene and beta-carotene. The carotenoid biosynthesis gene cluster of S. coelicolor consists of two convergent operons, crtEIBV and crtYTU, as previously shown for Streptomyces griseus. The crtEIBV null mutant completely lost its ability to produce carotenoids. The crt gene cluster is flanked by a regulatory region that consists of two divergent operons, litRQ and litSAB. The lit (light-induced transcription) genes encode a MerR-type transcriptional regulator (LitR), a possible oxidoreductase (LitQ), an extracytoplasmic function sigma factor (sigmaLitS), a putative lipoprotein (LitA), and a putative anti-sigma factor (LitB). S1 protection assay revealed that the promoters preceding crtE (PcrtE), crtY (PcrtY), litR (PlitR), and litS (PlitS) are activated upon illumination. A litS mutant lost both the ability to produce carotenoids and the activities of PcrtE, PcrtY, and PlitS, which suggested that sigmaLitS directs light-induced transcription from these promoters. An RNA polymerase holocomplex containing purified sigmaLitS recombinant protein generated specific PcrtE and PcrtY transcripts in an in vitro runoff transcriptional assay. A litR mutant that had an insertion of the kanamycin resistance gene was defective both in the ability to produce carotenoids and in all of the light-dependent promoter activities. Overexpression of litS resulted in constitutive carotenoid production in both the wild type and the litR mutant. These results indicate that sigmaLitS acts as a light-induced sigma factor that directs transcription of the crt biosynthesis gene cluster, whose activity is controlled by an unknown LitR function. This is the first report to describe light-inducible gene expression in Streptomyces.
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Affiliation(s)
- Hideaki Takano
- Life Science Research Center, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa 252-8510, Japan
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29
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Whitworth DE, Bryan SJ, Berry AE, McGowan SJ, Hodgson DA. Genetic dissection of the light-inducible carQRS promoter region of Myxococcus xanthus. J Bacteriol 2004; 186:7836-46. [PMID: 15547254 PMCID: PMC529085 DOI: 10.1128/jb.186.23.7836-7846.2004] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Myxococcus xanthus photoprotective carotenoids are produced in response to illumination due to regulated expression of carotenoid biosynthesis genes at two loci. Induction of the carotenogenesis regulon is dependent on expression of the carQRS operon. The first gene product of the operon, CarQ, is a sigma factor belonging to the ECF family and is responsible for light-dependent initiation of transcription at the carQRS promoter. We defined the minimal carQRS promoter as a 145-bp fragment of DNA upstream of the carQRS transcriptional start site, which includes the promoter for a divergent gene, gufA. In order to elucidate regions with the promoter required for activity, point mutations were introduced into the carQRS promoter between positions -151 and 6. While most sequence changes abolished carQRS promoter activity, two changes enhanced promoter activity and two changes caused the mutant promoter to become constitutive and independent of CarQ. The promoter-null point mutations and 6-bp deletion mutations implied that the carQRS promoter requires a functional gufA promoter for transcriptional activity and vice versa. By mapping the extent of the promoter region, identifying sequences important for promoter activity, and highlighting potential topological effects, we provide a foundation for further analysis of the carQRS promoter.
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Affiliation(s)
- David E Whitworth
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
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30
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Pérez-Marín MC, López-Rubio JJ, Murillo FJ, Elías-Arnanz M, Padmanabhan S. The N terminus of Myxococcus xanthus CarA repressor is an autonomously folding domain that mediates physical and functional interactions with both operator DNA and antirepressor protein. J Biol Chem 2004; 279:33093-103. [PMID: 15163666 DOI: 10.1074/jbc.m405225200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Expression of the Myxococcus xanthus carB operon, which encodes the majority of the enzymes involved in light-induced carotenogenesis, is down-regulated in the dark by the CarA repressor binding to its bipartite operator. CarS, produced on illumination, relieves repression of carB by physically interacting with CarA to dis-mantle CarA-DNA complexes. Here, we demonstrate that the N- and C-terminal portions of CarA are organized as distinct structural and functional domains. Specifically, we show that the 78 N-terminal residues of CarA, CarA(Nter), form a monomeric, highly helical, autonomously folding unit with significant structural stability. Significantly, CarA(Nter) houses both the operator and CarS binding specificity determinants of CarA. CarA(Nter) binds operator with a lower affinity than whole CarA, and the CarA(Nter)-CarS complex has a 1:1 stoichiometry. In vitro, sufficiently high concentrations of CarA(Nter) block M. xanthus RNA polymerase-promoter binding, and this is relieved by CarS. In vivo, substitution of the gene carA by that for CarA(Nter) results in constitutive expression of carB just as in a carA-deleted background. However, re-engineering the latter strain to overexpress CarA(Nter) restores repression of carB. Thus, the 78-residue N-terminal portion of CarA is an autonomously folded, dual function domain that orchestrates specific DNA-protein and protein-protein interactions and, when overexpressed, can be functionally competent in vivo.
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Affiliation(s)
- Mari Cruz Pérez-Marín
- Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, Murcia 30071, Spain
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31
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López-Rubio JJ, Padmanabhan S, Lázaro JM, Salas M, Murillo FJ, Elías-Arnanz M. Operator design and mechanism for CarA repressor-mediated down-regulation of the photoinducible carB operon in Myxococcus xanthus. J Biol Chem 2004; 279:28945-53. [PMID: 15123730 DOI: 10.1074/jbc.m403459200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The carB operon encodes all except one of the enzymes involved in light-induced carotenogenesis in Myxococcus xanthus. Expression of its promoter (P(B)) is repressed in the dark by sequence-specific DNA binding of CarA to a palindrome (pI) located between positions -47 and -64 relative to the transcription start site. This promotes subsequent binding of CarA to additional sites that remain to be defined. CarS, produced in the light, interacts physically with CarA, abrogates CarA-DNA binding, and thereby derepresses P(B). In this study, we delineate the operator design that exists for CarA by precisely mapping out the second operator element. For this, we examined how stepwise deletions and site-directed mutagenesis in the region between the palindrome and the transcription start site affect CarA binding around P(B) in vitro and expression of P(B) in vivo. These revealed the second operator element to be an imperfect interrupted palindrome (pII) spanning positions -26 to -40. In vitro assays using purified M. xanthus RNA polymerase showed that CarA abolishes P(B)-RNA polymerase binding and runoff transcription and that both were restored by CarS, thus rationalizing the observations in vivo. CarA binding to pII (after association with pI) effectively occludes RNA polymerase from P(B) and so provides the operative mechanism for the repression of the carB operon by CarA. The bipartite operator design, whereby transcription is blocked by the low affinity CarA-pII binding and is readily restored by CarS, may have evolved to match the needs for a rapid and an effective response to light.
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Affiliation(s)
- José Juan López-Rubio
- Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, Murcia 30071
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32
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Teramoto M, Takaichi S, Inomata Y, Ikenaga H, Misawa N. Structural and functional analysis of a lycopene beta-monocyclase gene isolated from a unique marine bacterium that produces myxol. FEBS Lett 2003; 545:120-6. [PMID: 12804761 DOI: 10.1016/s0014-5793(03)00513-1] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A gene coding for lycopene beta-monocyclase, which metabolizes lycopene (psi,psi-carotene) to gamma-carotene (beta,psi-carotene), was isolated for the first time from a unique marine bacterium strain P99-3 that produces myxol (a gamma-carotene derivative). This lycopene beta-monocyclase gene (designated crtYm) was included in the gene cluster which contained carotenoid biosynthetic gene (crtI, crtB, crtZ, crtY, and crtA) homologs. CrtYm, the CrtY homolog, metabolized lycopene to gamma-carotene, which was confirmed by deletion/expression analysis of the crtYm and by subsequent analysis of the metabolites from lycopene based on the retention times on high-performance liquid chromatography, UV-visible absorption spectra, and mass spectrometry.
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Affiliation(s)
- Maki Teramoto
- Marine Biotechnology Institute, 3-75-1 Heita, Kamaishi-shi, Iwate 026-0001, Japan.
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33
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Browning DF, Whitworth DE, Hodgson DA. Light-induced carotenogenesis in Myxococcus xanthus: functional characterization of the ECF sigma factor CarQ and antisigma factor CarR. Mol Microbiol 2003; 48:237-51. [PMID: 12657058 DOI: 10.1046/j.1365-2958.2003.03431.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Illumination of dark-grown Myxococcus xanthus with blue light leads to the induction of carotenoid synthesis. Central to this response is the activation of the light-inducible promoter, PcarQRS, and the transcription of three downstream genes, carQ, carR and carS. Sequence analysis predicted that CarQ is a member of the ECF (extracytoplasmic function) subfamily of RNA polymerase sigma factors, and that CarR is an inner membrane protein. Genetic analysis strongly implied that CarR is an antisigma factor that sequesters CarQ in a transcriptionally inactive complex. Using in vitro transcription run-off assays, we present biochemical evidence that CarQ functions as a bacterial sigma factor and is responsible for transcription initiation at PcarQRS. Similar experiments using the crtI promoter failed to implicate CarQ in direct transcription of the crtI gene. Experiments using the yeast two-hybrid system demonstrated a protein-protein interaction between CarQ and CarR, providing evidence of a CarQ-CarR complex. The yeast two-hybrid system data also indicated that CarR is capable of oligomerization. Fractionation of M. xanthus membranes with the detergent sarkosyl showed that CarR was associated with the inner membrane. Furthermore, CarR was found to be unstable in illuminated stationary phase cells, providing a possible mechanism by which the CarR-CarQ complex is disrupted.
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Affiliation(s)
- Douglas F Browning
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
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34
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Fontes M, Galbis-Martínez L, Murillo FJ. A novel regulatory gene for light-induced carotenoid synthesis in the bacterium Myxococcus xanthus. Mol Microbiol 2003; 47:561-71. [PMID: 12519205 DOI: 10.1046/j.1365-2958.2003.03319.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Myxococcus xanthus cells respond to blue light by producing carotenoids. Light triggers a network of regulatory actions that lead to the transcriptional activation of the carotenoid genes. By screening the colour phenotype of a collection of Tn5-lac insertion mutants, we have isolated a new mutant devoid of carotenoid synthesis. We map the transposon insertion, which co-segregates with the mutant phenotype, to a previously unknown gene designated here as carF. An in frame deletion within carF causes the same phenotype as the Tn5-lac insertion. The carF deletion prevents the activation of the normally light-inducible genes, without affecting the expression of any of the regulatory genes known to be expressed in a light-independent manner. Until now, the switch that sets off the regulatory cascade had been identified with light-driven inactivation of protein CarR, an antisigma factor. The exact mechanism of this inactivation has remained elusive. We show by epistatic analysis that the carF gene product participates in the light-dependent inactivation of CarR. The predicted CarF amino acid sequence reveals no known prokaryotic homologues. On the other hand, CarF is remarkably similar to Kua, a family of proteins of unknown function that is widely distributed among eukaryotes.
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Affiliation(s)
- Marta Fontes
- Departamento de Genética y Microbiología, Facultad de Biologie, Universidad de Murcia, Spain
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35
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Peck RF, Johnson EA, Krebs MP. Identification of a lycopene beta-cyclase required for bacteriorhodopsin biogenesis in the archaeon Halobacterium salinarum. J Bacteriol 2002; 184:2889-97. [PMID: 12003928 PMCID: PMC135044 DOI: 10.1128/jb.184.11.2889-2897.2002] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Biogenesis of the light-driven proton pump bacteriorhodopsin in the archaeon Halobacterium salinarum requires coordinate synthesis of the bacterioopsin apoprotein and carotenoid precursors of retinal, which serves as a covalently bound cofactor. As a step towards elucidating the mechanism and regulation of carotenoid metabolism during bacteriorhodopsin biogenesis, we have identified an H. salinarum gene required for conversion of lycopene to beta-carotene, a retinal precursor. The gene, designated crtY, is predicted to encode an integral membrane protein homologous to lycopene beta-cyclases identified in bacteria and fungi. To test crtY function, we constructed H. salinarum strains with in-frame deletions in the gene. In the deletion strains, bacteriorhodopsin, retinal, and beta-carotene were undetectable, whereas lycopene accumulated to high levels ( approximately 1.3 nmol/mg of total cell protein). Heterologous expression of H. salinarum crtY in a lycopene-producing Escherichia coli strain resulted in beta-carotene production. These results indicate that H. salinarum crtY encodes a functional lycopene beta-cyclase required for bacteriorhodopsin biogenesis. Comparative sequence analysis yields a topological model of the protein and provides a plausible evolutionary connection between heterodimeric lycopene cyclases in bacteria and bifunctional lycopene cyclase-phytoene synthases in fungi.
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Affiliation(s)
- Ronald F Peck
- Department of Biomolecular Chemistry, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA
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36
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Cervantes M, Murillo FJ. Role for vitamin B(12) in light induction of gene expression in the bacterium Myxococcus xanthus. J Bacteriol 2002; 184:2215-24. [PMID: 11914353 PMCID: PMC134944 DOI: 10.1128/jb.184.8.2215-2224.2002] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A light-inducible promoter (P(B)) drives the carB operon (carotenoid genes) of the bacterium Myxococcus xanthus. A gene encoding a regulator of carotenoid biosynthesis was identified by studying mutant strains carrying a transcriptional fusion to P(B) and deletions in three candidate genes. Our results prove that the identified gene, named carA, codes for a repressor of the P(B) promoter in the dark. They also show that the carA gene product does not participate in the light activation of two other promoters connected with carotenoid synthesis or its regulation in M. xanthus. CarA is a novel protein consisting of a DNA-binding domain of the family of MerR helix-turn-helix transcriptional regulators, directly joined to a cobalamin-binding domain. In support of this, we report here that the presence of vitamin B(12) or some other cobalamin derivatives is absolutely required for activation of the P(B) promoter by light.
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Affiliation(s)
- María Cervantes
- Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, 30100 Murcia, Spain
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37
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López-Rubio JJ, Elías-Arnanz M, Padmanabhan S, Murillo FJ. A repressor-antirepressor pair links two loci controlling light-induced carotenogenesis in Myxococcus xanthus. J Biol Chem 2002; 277:7262-70. [PMID: 11748235 DOI: 10.1074/jbc.m110351200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The light-inducible carB operon encodes all but one of the structural genes for carotenogenesis in Myxococcus xanthus. It is transcriptionally controlled by two proteins expressed from two unlinked genetic loci: CarS from the light-inducible carQRS operon, and CarA from the light-independent carA operon. CarA represses transcription from the carB promoter (P(B)) in the dark, and CarS counteracts this on illumination. The CarA sequence revealed a helix-turn-helix DNA-binding motif of the type found in bacterial MerR transcriptional factors, whereas CarS contains no known DNA-binding motif. Here, we examine the molecular interplay between CarA and CarS. We demonstrate the following. (i) Whereas CarS exhibits no DNA binding in vitro, CarA binds specifically to a region encompassing P(B) to form at least two distinct complexes. (ii) A palindrome located between positions -46 and -63 relative to the transcription start point is essential but not sufficient for the formation of the two CarA-DNA complexes observed. (iii) CarS abrogates the specific DNA binding of CarA. CarA is therefore a repressor and CarS an antirepressor. (iv) CarS physically interacts with CarA; thus, the functional interaction between them is mediated by protein-protein interactions.
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Affiliation(s)
- José Juan López-Rubio
- Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, Murcia 30071, Spain
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38
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Whitworth DE, Hodgson DA. Light-induced carotenogenesis in Myxococcus xanthus: evidence that CarS acts as an anti-repressor of CarA. Mol Microbiol 2001; 42:809-19. [PMID: 11722744 DOI: 10.1046/j.1365-2958.2001.02679.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the bacterium Myxococcus xanthus, carotenoids are produced in response to illumination, as a result of expression of the crt carotenoid biosynthesis genes. The majority of crt genes are clustered in the crtEBDC operon, which is repressed in the dark by CarA. Genetic data suggest that, in the light, CarS is synthesized and achieves activation of the crtEBDC operon by removing the repressive action of CarA. As CarS contains no known DNA-binding motif, the relief of CarA-mediated repression was postulated to result from a direct interaction between these two proteins. Use of the yeast two-hybrid system demonstrated direct interaction between CarA and CarS. The two-hybrid system also implied that CarA and, possibly, CarS are capable of homodimerization. Direct evidence for CarS anti-repressor action was provided in vitro. A glutathione S-transferase (GST)-CarA protein fusion was shown to bind specifically to a palindromic operator sequence within the crtEBDC promoter. CarA was prevented from binding to its operator, and prebound CarA was removed by the addition of purified CarS. CarS is therefore an anti-repressor.
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Affiliation(s)
- D E Whitworth
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
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39
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Krubasik P, Kobayashi M, Sandmann G. Expression and functional analysis of a gene cluster involved in the synthesis of decaprenoxanthin reveals the mechanisms for C50 carotenoid formation. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:3702-8. [PMID: 11432736 DOI: 10.1046/j.1432-1327.2001.02275.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Corynebacterium glutamicum accumulates the C50 carotenoid decaprenoxanthin. Rescued DNA from transposon color mutants of this Gram-positive bacterium was used to clone the carotenoid biosynthetic gene cluster. By sequence comparison and functional complementation, the genes involved in the synthesis of carotenoids with 50 carbon atoms were identified. The genes crtE, encoding a geranylgeranyl pyrophosphate synthase, crtB, encoding a phytoene synthase, and crtI, encoding a phytoene desaturase, are responsible for the formation of lycopene. The products of three novel genes, crtYe and crtYf, with sequence similarities to heterodimeric lycopene cyclase crtYc and crtYd, together with crtEb which exhibits a prenyl transferase motif, were involved in the conversion of C40 acyclic lycopene to cyclic C50 carotenoids. Using functional complementation in Escherichia coli, it could be shown that the elongation of lycopene to the acyclic C50 carotenoid flavuxanthin by the addition of C5 isoprenoid units at positions C-2 and C-2' is catalyzed by the crtEb gene product. Subsequently, the gene products of crtYe and crtYf in a concerted action convert the acyclic flavuxanthin into the cyclic C50 carotene, decaprenoxanthin, forming two epsilon-ionone groups. The mechanisms, involving two individual steps for the formation of cyclic C50 carotenoids from lycopene, are proposed on the basis of these results.
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Affiliation(s)
- P Krubasik
- Botanisches Institut, Goethe Universität, Frankfurt, Germany
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40
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Yamada RH, Kera Y, Toi H, Hayashi T, Arimoto K, Takahashi M, Iwazaki I, Yamashita S. Microbial oxidases of acidic d-amino acids. ACTA ACUST UNITED AC 2001. [DOI: 10.1016/s1381-1177(00)00208-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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41
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Moreno AJ, Fontes M, Murillo FJ. ihfA gene of the bacterium Myxococcus xanthus and its role in activation of carotenoid genes by blue light. J Bacteriol 2001; 183:557-69. [PMID: 11133949 PMCID: PMC94911 DOI: 10.1128/jb.183.2.557-569.2001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Myxococcus xanthus responds to blue light by producing carotenoids. Several regulatory genes are known that participate in the light action mechanism, which leads to the transcriptional activation of the carotenoid genes. We had already reported the isolation of a carotenoid-less, Tn5-induced strain (MR508), whose mutant site was unlinked to the indicated regulatory genes. Here, we show that OmegaMR508::Tn5 affects all known light-inducible promoters in different ways. It blocks the activation of two of them by light but makes the activity of a third one light independent. The OmegaMR508 locus has been cloned and sequenced. The mutation had occurred at the promoter of a gene we propose is the M. xanthus ortholog of ihfA. This encodes the alpha subunit of the histone-like integration host factor protein. An in-frame deletion within ihfA causes the same effects as the OmegaMR508::Tn5 insertion. Like other IhfA proteins, the deduced amino acid sequence of M. xanthus IhfA shows much similarity to HU, another histone-like protein. Sequence comparison data, however, and the finding that the M. xanthus gene is preceded by gene pheT, as happens in other gram-negative bacteria, strongly argue for the proposed orthology relationship. The M. xanthus ihfA gene shows some unusual features, both from structural and physiological points of view. In particular, the protein is predicted to have a unique, long acidic extension at the carboxyl terminus, and it appears to be necessary for normal cell growth and even vital for a certain wild-type strain of M. xanthus.
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Affiliation(s)
- A J Moreno
- Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, 30100 Murcia, Spain
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42
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Velayos A, Eslava AP, Iturriaga EA. A bifunctional enzyme with lycopene cyclase and phytoene synthase activities is encoded by the carRP gene of Mucor circinelloides. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:5509-19. [PMID: 10951210 DOI: 10.1046/j.1432-1327.2000.01612.x] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Using functional analyses in Escherichia coli and Mucor circinelloides, it has been shown that a single M. circinelloides gene (carRP) codes for a protein with two different enzymatic activities, lycopene cyclase and phytoene synthase, which are encoded by independent genes in organisms other than fungi. This gene was identified using complementation tests among different classes of carotenoid mutants of M. circinelloides. The carRP gene product contains two domains: the R domain is located at the N-terminus and determines lycopene cyclase activity; the P domain is located at the C-terminus and displays phytoene synthase activity. The R domain is functional even in the absence of the P domain, while the latter needs the proper R domain conformation to carry out its function. The carRP gene is closely linked to the phytoene dehydrogenase (carB) gene, and the promoter regions of both genes are located within only 446 bp. Northern analyses show a co-ordinated regulation of the expression of both genes by blue light. Several motifs found in this promoter region suggest a bi-directional mode of transcription control.
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Affiliation(s)
- A Velayos
- Area de Genética, Departamento de Microbiología y Genética, Universidad de Salamanca, Spain
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Viveiros M, Krubasik P, Sandmann G, Houssaini-Iraqui M. Structural and functional analysis of the gene cluster encoding carotenoid biosynthesis in Mycobacterium aurum A+. FEMS Microbiol Lett 2000; 187:95-101. [PMID: 10828407 DOI: 10.1111/j.1574-6968.2000.tb09143.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The fragment containing the carotenoid gene cluster from Mycobacterium aurum A+, a 3,3'-dihydroxy-isoneriatene and 3-monohydroxy-isoneriatene accumulator, has been sequenced and the exposed eight genes are organised in two operons. The function of three of these genes, a phytoene desaturase (crtI), a phytoene cyclase (crtY) and a beta-carotene desaturase (crtU), was demonstrated by complementation of M. aurum carotenoid mutants. The eight genes of the carotenoid cluster are highly homologous to other carotenoid gene clusters and thus this cluster is a candidate for its introduction into mycobacteria as a non-antibiotic reporter gene(s) as well as a source of new regulated promoters.
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Affiliation(s)
- M Viveiros
- Unidade de Micobactérias e Centro de Malaria e Outras Doenças Tropicais, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Portugal.
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44
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Abstract
A mechanism for regulating gene expression at the level of transcription utilizes an antagonist of the sigma transcription factor known as the anti-sigma (anti-sigma) factor. The cytoplasmic class of anti-sigma factors has been well characterized. The class includes AsiA form bacteriophage T4, which inhibits Escherichia coli sigma 70; FlgM, present in both gram-positive and gram-negative bacteria, which inhibits the flagella sigma factor sigma 28; SpoIIAB, which inhibits the sporulation-specific sigma factor, sigma F and sigma G, of Bacillus subtilis; RbsW of B. subtilis, which inhibits stress response sigma factor sigma B; and DnaK, a general regulator of the heat shock response, which in bacteria inhibits the heat shock sigma factor sigma 32. In addition to this class of well-characterized cytoplasmic anti-sigma factors, a new class of homologous, inner-membrane-bound anti-sigma factors has recently been discovered in a variety of eubacteria. This new class of anti-sigma factors regulates the expression of so-called extracytoplasmic functions, and hence is known as the ECF subfamily of anti-sigma factors. The range of cell processes regulated by anti-sigma factors is highly varied and includes bacteriophage phage growth, sporulation, stress response, flagellar biosynthesis, pigment production, ion transport, and virulence.
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Affiliation(s)
- K T Hughes
- Department of Microbiology, University of Washington, Seattle 98195, USA.
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Martínez-Argudo I, Ruiz-Vázquez RM, Murillo FJ. The structure of an ECF-sigma-dependent, light-inducible promoter from the bacterium Myxococcus xanthus. Mol Microbiol 1998; 30:883-93. [PMID: 10094635 DOI: 10.1046/j.1365-2958.1998.01129.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Expression of the Myxococcus xanthus gene crtl is controlled by a light-inducible promoter. The activity of this promoter depends on CarQ, a sigma factor of the extracytoplasmic function (ECF) subfamily. Here, we show thatthe minimum DNA stretch reproducing normal expression of crtl extends from a few bases upstream of the -35 position to a site well downstream of the transcriptional start. The downstream DNA contains an enhancer-like element that remains active when displaced upstream of the promoter. Experimental evidence is provided for the activity of the crtl promoter being critically dependent on a pentanucleotide sequence centred at the -31 position. The similarity of this sequence with the consensus for ECF-sigma-dependent promoters from other bacteria is discussed. The activity of the crtl promoter also depends on certain basepairs at the -10 region. Hence, the operation of ECF-sigma-factors seems to require binding to two different DNA sites, although the -10 sequences of different ECF-sigma-dependent promoters are unrelated to one another, and the ECF-sigma-factors themselves lack the conserved domain known to mediate binding of other sigma-factors to the -10 DNA site.
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Affiliation(s)
- I Martínez-Argudo
- Departamento de Genética y Microbiología, Facultad de Biologia, Universidad de Murcia, Spain
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46
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Passoja K, Myllyharju J, Pirskanen A, Kivirikko KI. Identification of arginine-700 as the residue that binds the C-5 carboxyl group of 2-oxoglutarate in human lysyl hydroxylase 1. FEBS Lett 1998; 434:145-8. [PMID: 9738467 DOI: 10.1016/s0014-5793(98)00966-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Lysyl hydroxylase catalyzes the formation of hydroxylysine in collagens by a reaction that involves oxidative decarboxylation of 2-oxoglutarate. Its binding site can be divided into two main subsites: subsite I consists of a positively charged side-chain which binds the C-5 carboxyl group, while subsite II consists of two coordination sites of the enzyme-bound Fe2+ and is chelated by the C-1-C-2 moiety. In order to identify subsite I, we converted Arg-697, Arg-700 and Ser-705 individually to alanine and Arg-700 also to lysine, and expressed the mutant enzymes in insect cells. Arg-700-Ala inactivated lysyl hydroxylase completely, whereas Arg-697-Ala and Ser-723-Ala had only a relatively minor effect. Arg-700-Lys produced 93% inactivation under standard assay conditions, the main effect being a 10-fold increase in the Km for 2-oxoglutarate, whereas the Vmax was unchanged. Arg-700 thus provides the positively charged residue that binds the C-5 carboxyl group of 2-oxoglutarate, whereas Ser-705 appears to be of no functional significance in this binding.
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Affiliation(s)
- K Passoja
- Biocenter and Department of Medical Biochemistry, University of Oulu, Finland
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Perzl M, Reipen IG, Schmitz S, Poralla K, Sahm H, Sprenger GA, Kannenberg EL. Cloning of conserved genes from Zymomonas mobilis and Bradyrhizobium japonicum that function in the biosynthesis of hopanoid lipids. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1393:108-18. [PMID: 9714766 DOI: 10.1016/s0005-2760(98)00064-2] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The squalene-hopene cyclase (SHC) is the only enzyme involved in the biosynthesis of hopanoid lipids that has been characterized on the genetic level. To investigate if additional genes involved in hopanoid biosynthesis are clustered with the shc gene, we cloned and analyzed the nucleotide sequences located immediately upstream of the shc genes from Zymomonas mobilis and Bradyrhizobium japonicum. In Z. mobilis, five open reading frames (ORFs, designated as hpnA-E) were detected in a close arrangement with the shc gene. In B. japonicum, three similarly arranged ORFs (corresponding to hpnC-E from Z. mobilis) were found. The deduced amino acid sequences of hpnC-E showed significant similarity (58-62%) in both bacteria. Similarities to enzymes of other terpenoid biosynthesis pathways (carotenoid and steroid biosynthesis) suggest that these ORFs encode proteins involved in the biosynthesis of hopanoids and their intermediates. Expression of hpnC to hpnE from Z. mobilis as well as expression of hpnC from B. japonicum in Escherichia coli led to the formation of the hopanoid precursor squalene. This indicates that hpnC encodes a squalene synthase. The two additional ORFs (hpnA and hpnB) in Z. mobilis showed similarities to enzymes involved in the transfer and modification of sugars, indicating that they may code for enzymes involved in the biosynthesis of the complex, sugar-containing side chains of hopanoids.
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Affiliation(s)
- M Perzl
- Mikrobiologie/Biotechnologie, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany
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Fukunaga S, Yuno S, Takahashi M, Taguchi S, Kera Y, Odani S, Yamada RH. Purification and properties of d-glutamate oxidase from Candida boidinii 2201. ACTA ACUST UNITED AC 1998. [DOI: 10.1016/s0922-338x(98)80008-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Abstract
Carotenoids represent one of the most widely distributed and structurally diverse classes of natural pigments, with important functions in photosynthesis, nutrition, and protection against photooxidative damage. In the eubacterial community, yellow, orange, and red carotenoids are produced by anoxygenic photosynthetic bacteria, cyanobacteria, and certain species of nonphotosynthetic bacteria. Many eukaryotes, including all algae and plants, as well as some fungi, also synthesize these pigments. In noncarotenogenic organisms, such as mammals, birds, amphibians, fish, crustaceans, and insects, dietary carotenoids and their metabolites also serve important biological roles. Within the last decade, major advances have been made in the elucidation of the molecular genetics, the biochemistry, and the regulation of eubacterial carotenoid biosynthesis. These developments have important implications for eukaryotes, and they make increasingly attractive the genetic manipulation of carotenoid content for biotechnological purposes.
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Affiliation(s)
- G A Armstrong
- Institute for Plant Sciences, Plant Genetics, Swiss Federal Institute of Technology (ETH), Zürich.
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50
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Ramakrishnan L, Tran HT, Federspiel NA, Falkow S. A crtB homolog essential for photochromogenicity in Mycobacterium marinum: isolation, characterization, and gene disruption via homologous recombination. J Bacteriol 1997; 179:5862-8. [PMID: 9294446 PMCID: PMC179478 DOI: 10.1128/jb.179.18.5862-5868.1997] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
A gene essential for light-induced pigment production was isolated from the photochromogen Mycobacterium marinum by heterologous complementation of an M. marinum cosmid library in the nonchromogen Mycobacterium smegmatis. This gene is part of an operon and homologous to the Streptomyces griseus and Myxococcus xanthus crtB genes encoding phytoene synthase. Gene replacement at this locus was achieved via homologous recombination, demonstrating that its expression is essential for photochromogenicity. The ease of targeted gene disruption in this pathogenic Mycobacterium allows for the dissection of the molecular basis of mycobacterial pathogenesis.
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Affiliation(s)
- L Ramakrishnan
- Department of Microbiology and Immunology, Stanford University School of Medicine, California 94305-5402, USA.
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