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Yang X, Zhang J, Zhu J, Yang R, Tong Y. Molecular insights into FucR transcription factor to control the metabolism of L-fucose in Bifidobacterium longum subsp. infantis. Microbiol Res 2024; 283:127709. [PMID: 38593579 DOI: 10.1016/j.micres.2024.127709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 03/27/2024] [Accepted: 03/30/2024] [Indexed: 04/11/2024]
Abstract
Bifidobacterium longum subsp. infantis commonly colonizes the human gut and is capable of metabolizing L-fucose, which is abundant in the gut. Multiple studies have focused on the mechanisms of L-fucose utilization by B. longum subsp. infantis, but the regulatory pathways governing the expression of these catabolic processes are still unclear. In this study, we have conducted a structural and functional analysis of L-fucose metabolism transcription factor FucR derived from B. longum subsp. infantis Bi-26. Our results indicated that FucR is a L-fucose-sensitive repressor with more α-helices, fewer β-sheets, and β-turns. Transcriptional analysis revealed that FucR displays weak negative self-regulation, which is counteracted in the presence of L-fucose. Isothermal titration calorimetry indicated that FucR has a 2:1 stoichiometry with L-fucose. The key amino acid residues for FucR binding L-fucose are Asp280 and Arg331, with mutation of Asp280 to Ala resulting in a decrease in the affinity between FucR and L-fucose with the Kd value from 2.58 to 11.68 μM, and mutation of Arg331 to Ala abolishes the binding ability of FucR towards L-fucose. FucR specifically recognized and bound to a 20-bp incomplete palindrome sequence (5'-ACCCCAATTACGAAAATTTTT-3'), and the affinity of the L-fucose-loaded FucR for the DNA fragment was lower than apo-FucR. The results provided new insights into the regulating L-fucose metabolism by B. longum subsp. infantis.
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Affiliation(s)
- Xiaojun Yang
- School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu 214122, China
| | - Jing Zhang
- School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu 214122, China
| | - Jing Zhu
- School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu 214122, China
| | - Ruijin Yang
- State Key Laboratory of Food Science and Resources, Jiangnan University, Wuxi, Jiangsu 214122, China; School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu 214122, China
| | - Yanjun Tong
- School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu 214122, China.
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2
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Carrillo Rincón AF, Farny NG. Unlocking the strength of inducible promoters in Gram-negative bacteria. Microb Biotechnol 2023; 16:961-976. [PMID: 36738130 PMCID: PMC10128130 DOI: 10.1111/1751-7915.14219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 01/02/2023] [Accepted: 01/07/2023] [Indexed: 02/05/2023] Open
Abstract
Inducible bacterial promoters are ubiquitous biotechnology tools that have a consistent architecture including two key elements: the operator region recognized by the transcriptional regulatory proteins, and the -10 and -35 consensus sequences required to recruit the sigma (σ) 70 subunits of RNA polymerase to initiate transcription. Despite their widespread use, leaky transcription in the OFF state remains a challenge. We have updated the architecture of the lac and tet promoters to improve their strength, control and portability by the adaptation of the consensus -10 and -35 sequence boxes strongly targeted by σ70 , incorporation of a strong ribosome binding site recognized broadly by Gram-negative bacteria, and independent control of the transcriptional regulators by constitutive promoters. To test the promoters, we use the far-red fluorescent protein mCardinal, which significantly improves the signal-to-background ratio of promoter measurements over widely utilized green fluorescent proteins. We validate the improvement in OFF state control and inducibility by demonstrating production of the toxic and aggregate-prone cocaine esterase enzyme CocE. We further demonstrate portability of the promoters to additional Gram-negative species Pseudomonas putida and Vibrio natriegens. Our results represent a significant improvement over existing protein expression systems that will enable advances in protein production for various biotechnology applications.
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Affiliation(s)
| | - Natalie G Farny
- Department of Biology and Biotechnology, Worcester Polytechnic Institute, Worcester, Massachusetts, USA
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3
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Development and Application of Two Inducible Expression Systems for Streptococcus suis. Microbiol Spectr 2022; 10:e0036322. [PMID: 35758678 PMCID: PMC9430170 DOI: 10.1128/spectrum.00363-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Streptococcus suis is an important zoonotic bacterial pathogen posing a threat to the pig industry as well as public health, for which the mechanisms of growth and cell division remain largely unknown. Developing convenient genetic tools that can achieve strictly controlled gene expression is of great value for investigating these fundamental physiological processes of S. suis. In this study, we first identified three strong constitutive promoters, Pg, Pt, and Pe, in S. suis. Promoter Pg was used to drive the expression of repressor genes tetR and lacI, and the operator sequences were added within promoters Pt and Pe. By optimizing the insertion sites of the operator sequence, we successfully constructed an anhydrotetracycline (ATc)-inducible expression system and an isopropyl-β-d-thiogalactopyranoside (IPTG)-inducible expression system in S. suis. We showed that these two systems provided inducer-concentration- and induction-time-dependent expression of the reporter gene. By using these tools, we investigated the subcellular localization of a key cell division protein, FtsZ, which showed that it could be correctly localized to the midcell region. In addition, we constructed a conditional knockout strain for the glmS gene, which is an essential gene, and showed that our ATc-inducible promoter could provide strictly controlled expression of glmS in trans, suggesting that our inducible expression systems can be used for deletion of essential genes in S. suis. Therefore, for the first time we developed two inducible expression systems in S. suis and showed their applications in the study of an important cell division protein and an essential gene. These genetic tools will further facilitate the functional study of other important genes of S. suis. IMPORTANCE Streptococcus suis is an important zoonotic bacterial pathogen. Studying the mechanisms of cell growth and division is important for the identification of novel antimicrobial drug targets. Inducible expression systems can provide strictly controlled expression of the protein of interest and are useful tools to study the functions of physiologically important proteins. However, there is a lack of convenient genetic tools that can achieve inducible protein expression in S. suis. In this study, we developed two (ATc-inducible and IPTG-inducible) inducible expression systems and showed their applications in a subcellular localization study of a cell division protein and the construction of conditional knockout of essential genes in S. suis. These systems will be useful for functional studies of important proteins of S. suis.
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4
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Wang Z, Mothi N, Muñoz V. Single-Molecule Fluorescence Spectroscopy Approaches for Probing Fast Biomolecular Dynamics and Interactions. Methods Mol Biol 2022; 2376:235-246. [PMID: 34845613 DOI: 10.1007/978-1-0716-1716-8_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Single-molecule fluorescence spectroscopy, and particularly its Förster resonance energy transfer implementation (SM-FRET), provides the opportunity to resolve the stochastic conformational fluctuations undergone by individual protein molecules while they fold-unfold, bind to their partners, or carry out catalysis. Such information is key to resolve the microscopic pathways and mechanisms underlying such processes, and cannot be obtained from bulk experiments. To fully resolve protein conformational dynamics, SM-FRET experiments need to reach microsecond, and even sub-microsecond, time resolutions. The key to reach such resolution lies in increasing the efficiency at which photons emitted by a single molecule are collected and detected by the instrument (photon count rates). In this chapter, we describe basic procedures that an end user can follow to optimize the confocal microscope optics in order to maximize the photon count rates. We also discuss the use of photoprotection cocktails specifically designed to reduce fluorophore triplet buildup at high irradiance (the major cause of limiting photon emission rates) while improving the mid-term photostability of the fluorophores. Complementary strategies based on the data analysis are discussed in depth by other authors in Chap. 14 .
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Affiliation(s)
- Zifan Wang
- Department of Bioengineering, University of California at Merced, Merced, CA, USA
- NSF CREST Center for Cellular and Biomolecular Machines (CCBM), University of California at Merced, Merced, CA, USA
| | - Nivin Mothi
- Chemistry and Chemical Biology Graduate Program, University of California at Merced, Merced, CA, USA
- NSF CREST Center for Cellular and Biomolecular Machines (CCBM), University of California at Merced, Merced, CA, USA
| | - Victor Muñoz
- Department of Bioengineering and Center for Cellular and Biomolecular Machines, University of California Merced, Merced, CA, USA.
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5
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Borne R, Vita N, Franche N, Tardif C, Perret S, Fierobe HP. Engineering of a new Escherichia coli strain efficiently metabolizing cellobiose with promising perspectives for plant biomass-based application design. Metab Eng Commun 2021; 12:e00157. [PMID: 33457204 PMCID: PMC7797564 DOI: 10.1016/j.mec.2020.e00157] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 11/24/2020] [Accepted: 12/14/2020] [Indexed: 11/30/2022] Open
Abstract
The necessity to decrease our fossil energy dependence requests bioprocesses based on biomass degradation. Cellobiose is the main product released by cellulases when acting on the major plant cell wall polysaccharide constituent, the cellulose. Escherichia coli, one of the most common model organisms for the academy and the industry, is unable to metabolize this disaccharide. In this context, the remodeling of E. coli to catabolize cellobiose should thus constitute an important progress for the design of such applications. Here, we developed a robust E. coli strain able to metabolize cellobiose by integration of a small set of modifications in its genome. Contrary to previous studies that use adaptative evolution to achieve some growth on this sugar by reactivating E. coli cryptic operons coding for cellobiose metabolism, we identified easily insertable modifications impacting the cellobiose import (expression of a gene coding a truncated variant of the maltoporin LamB, modification of the expression of lacY encoding the lactose permease) and its intracellular degradation (genomic insertion of a gene encoding either a cytosolic β-glucosidase or a cellobiose phosphorylase). Taken together, our results provide an easily transferable set of mutations that confers to E. coli an efficient growth phenotype on cellobiose (doubling time of 2.2 h in aerobiosis) without any prior adaptation.
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Affiliation(s)
| | | | | | - Chantal Tardif
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
| | - Stéphanie Perret
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
| | - Henri-Pierre Fierobe
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
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6
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Wilson CJ, Bommarius AS, Champion JA, Chernoff YO, Lynn DG, Paravastu AK, Liang C, Hsieh MC, Heemstra JM. Biomolecular Assemblies: Moving from Observation to Predictive Design. Chem Rev 2018; 118:11519-11574. [PMID: 30281290 PMCID: PMC6650774 DOI: 10.1021/acs.chemrev.8b00038] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Biomolecular assembly is a key driving force in nearly all life processes, providing structure, information storage, and communication within cells and at the whole organism level. These assembly processes rely on precise interactions between functional groups on nucleic acids, proteins, carbohydrates, and small molecules, and can be fine-tuned to span a range of time, length, and complexity scales. Recognizing the power of these motifs, researchers have sought to emulate and engineer biomolecular assemblies in the laboratory, with goals ranging from modulating cellular function to the creation of new polymeric materials. In most cases, engineering efforts are inspired or informed by understanding the structure and properties of naturally occurring assemblies, which has in turn fueled the development of predictive models that enable computational design of novel assemblies. This Review will focus on selected examples of protein assemblies, highlighting the story arc from initial discovery of an assembly, through initial engineering attempts, toward the ultimate goal of predictive design. The aim of this Review is to highlight areas where significant progress has been made, as well as to outline remaining challenges, as solving these challenges will be the key that unlocks the full power of biomolecules for advances in technology and medicine.
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Affiliation(s)
- Corey J. Wilson
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Andreas S. Bommarius
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Julie A. Champion
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Yury O. Chernoff
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
- Laboratory of Amyloid Biology & Institute of Translational Biomedicine, St. Petersburg State University, St. Petersburg 199034, Russia
| | - David G. Lynn
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Anant K. Paravastu
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Chen Liang
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Ming-Chien Hsieh
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Jennifer M. Heemstra
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
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7
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Tardin C. The mechanics of DNA loops bridged by proteins unveiled by single-molecule experiments. Biochimie 2017; 142:80-92. [PMID: 28804000 DOI: 10.1016/j.biochi.2017.08.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Accepted: 08/06/2017] [Indexed: 12/28/2022]
Abstract
Protein-induced DNA bridging and looping is a common mechanism for various and essential processes in bacterial chromosomes. This mechanism is preserved despite the very different bacterial conditions and their expected influence on the thermodynamic and kinetic characteristics of the bridge formation and stability. Over the last two decades, single-molecule techniques carried out on in vitro DNA systems have yielded valuable results which, in combination with theoretical works, have clarified the effects of different parameters of nucleoprotein complexes on the protein-induced DNA bridging and looping process. In this review, I will outline the features that can be measured for such processes with various single-molecule techniques in use in the field. I will then describe both the experimental results and the theoretical models that illuminate the contribution of the DNA molecule itself as well as that of the bridging proteins in the DNA looping mechanism at play in the nucleoid of E. coli.
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Affiliation(s)
- Catherine Tardin
- Institut de Pharmacologie et de Biologie Structurale, Université de Toulouse, CNRS, UPS, France.
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8
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Landete J. Effector Molecules and Regulatory Proteins: Applications. Trends Biotechnol 2016; 34:777-780. [DOI: 10.1016/j.tibtech.2016.04.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Revised: 04/22/2016] [Accepted: 04/25/2016] [Indexed: 10/21/2022]
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9
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Ghosh S, Ghosh C, Nandi S, Bhattacharyya K. Unfolding and refolding of a protein by cholesterol and cyclodextrin: a single molecule study. Phys Chem Chem Phys 2015; 17:8017-27. [DOI: 10.1039/c5cp00385g] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Cholesterol induced unfolding of a globular protein, human serum albumin (HSA), and β-cyclodextrin induced refolding of the unfolded protein is demonstrated in this study.
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Affiliation(s)
- Shirsendu Ghosh
- Department of Physical Chemistry
- Indian Association For The cultivation of Science
- Kolkata 700 032
- India
| | - Catherine Ghosh
- Department of Physical Chemistry
- Indian Association For The cultivation of Science
- Kolkata 700 032
- India
| | - Somen Nandi
- Department of Physical Chemistry
- Indian Association For The cultivation of Science
- Kolkata 700 032
- India
| | - Kankan Bhattacharyya
- Department of Physical Chemistry
- Indian Association For The cultivation of Science
- Kolkata 700 032
- India
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10
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Revalee JD, Blab GA, Wilson HD, Kahn JD, Meiners JC. Tethered particle motion reveals that LacI·DNA loops coexist with a competitor-resistant but apparently unlooped conformation. Biophys J 2014; 106:705-15. [PMID: 24507611 DOI: 10.1016/j.bpj.2013.12.024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Revised: 11/26/2013] [Accepted: 12/12/2013] [Indexed: 10/25/2022] Open
Abstract
The lac repressor protein (LacI) efficiently represses transcription of the lac operon in Escherichia coli by binding to two distant operator sites on the bacterial DNA and causing the intervening DNA to form a loop. We employed single-molecule tethered particle motion to observe LacI-mediated loop formation and breakdown in DNA constructs that incorporate optimized operator binding sites and intrinsic curvature favorable to loop formation. Previous bulk competition assays indirectly measured the loop lifetimes in these optimized DNA constructs as being on the order of days; however, we measured these same lifetimes to be on the order of minutes for both looped and unlooped states. In a range of single-molecule DNA competition experiments, we found that the resistance of the LacI-DNA complex to competitive binding is a function of both the operator strength and the interoperator sequence. To explain these findings, we present what we believe to be a new kinetic model of loop formation and DNA competition. In this proposed new model, we hypothesize a new unlooped state in which the unbound DNA-binding domain of the LacI protein interacts nonspecifically with nonoperator DNA adjacent to the operator site at which the second LacI DNA-binding domain is bound.
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Affiliation(s)
- Joel D Revalee
- Department of Physics, University of Michigan, Ann Arbor, Michigan
| | - Gerhard A Blab
- Debye Institute, Molecular Biophysics, Utrecht University, Utrecht, The Netherlands
| | - Henry D Wilson
- LSA Biophysics, University of Michigan, Ann Arbor, Michigan
| | - Jason D Kahn
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland
| | - Jens-Christian Meiners
- Department of Physics, University of Michigan, Ann Arbor, Michigan; LSA Biophysics, University of Michigan, Ann Arbor, Michigan.
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11
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Gnanakumar ES, Naik JM, Manikandan M, Raja T, Gopinath CS. Role of Nanointerfaces in Cu- and Cu+Au-Based Near-Ambient-Temperature CO Oxidation Catalysts. ChemCatChem 2014. [DOI: 10.1002/cctc.201402581] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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12
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Johnson S, van de Meent JW, Phillips R, Wiggins CH, Lindén M. Multiple LacI-mediated loops revealed by Bayesian statistics and tethered particle motion. Nucleic Acids Res 2014; 42:10265-77. [PMID: 25120267 PMCID: PMC4176382 DOI: 10.1093/nar/gku563] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The bacterial transcription factor LacI loops DNA by binding to two separate locations on the DNA simultaneously. Despite being one of the best-studied model systems for transcriptional regulation, the number and conformations of loop structures accessible to LacI remain unclear, though the importance of multiple coexisting loops has been implicated in interactions between LacI and other cellular regulators of gene expression. To probe this issue, we have developed a new analysis method for tethered particle motion, a versatile and commonly used in vitro single-molecule technique. Our method, vbTPM, performs variational Bayesian inference in hidden Markov models. It learns the number of distinct states (i.e. DNA–protein conformations) directly from tethered particle motion data with better resolution than existing methods, while easily correcting for common experimental artifacts. Studying short (roughly 100 bp) LacI-mediated loops, we provide evidence for three distinct loop structures, more than previously reported in single-molecule studies. Moreover, our results confirm that changes in LacI conformation and DNA-binding topology both contribute to the repertoire of LacI-mediated loops formed in vitro, and provide qualitatively new input for models of looping and transcriptional regulation. We expect vbTPM to be broadly useful for probing complex protein–nucleic acid interactions.
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Affiliation(s)
- Stephanie Johnson
- Department of Biochemistry and Molecular Biophysics, California Institute of Technology, 1200 E. California Blvd., Pasadena, California 91125
| | - Jan-Willem van de Meent
- Department of Statistics, Columbia University, 1255 Amsterdam Avenue MC 4690, New York, New York 10027
| | - Rob Phillips
- Departments of Applied Physics and Biology, California Institute of Technology, 1200 E. California Blvd., Pasadena, California 91125
| | - Chris H Wiggins
- Department of Applied Physics and Applied Mathematics, Columbia University, 200 S.W. Mudd, 500 W. 120th St. MC 4701, New York, New York 10027
| | - Martin Lindén
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, Svante Arrhenius väg 16C, SE-106 91 Stockholm, Sweden Department of Cell and Molecular Biology, Uppsala University, Box 256, SE-751 05 Uppsala, Sweden
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13
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Camsund D, Heidorn T, Lindblad P. Design and analysis of LacI-repressed promoters and DNA-looping in a cyanobacterium. J Biol Eng 2014; 8:4. [PMID: 24467947 PMCID: PMC3922697 DOI: 10.1186/1754-1611-8-4] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 12/26/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Cyanobacteria are solar-powered prokaryotes useful for sustainable production of valuable molecules, but orthogonal and regulated promoters are lacking. The Lac repressor (LacI) from Escherichia coli is a well-studied transcription factor that is orthogonal to cyanobacteria and represses transcription by binding a primary lac operator (lacO), blocking RNA-polymerase. Repression can be enhanced through DNA-looping, when a LacI-tetramer binds two spatially separated lacO and loops the DNA. Ptrc is a commonly used LacI-repressed promoter that is inefficiently repressed in the cyanobacterium Synechocystis PCC 6803. Ptrc2O, a version of Ptrc with two lacO, is more efficiently repressed, indicating DNA-looping. To investigate the inefficient repression of Ptrc and cyanobacterial DNA-looping, we designed a Ptrc-derived promoter library consisting of single lacO promoters, including a version of Ptrc with a stronger lacO (Ptrc1O-proximal), and dual lacO promoters with varying inter-lacO distances (the Ptrc2O-library). RESULTS We first characterized artificial constitutive promoters and used one for engineering a LacI-expressing strain of Synechocystis. Using this strain, we observed that Ptrc1O-proximal is similar to Ptrc in being inefficiently repressed. Further, the Ptrc2O-library displays a periodic repression pattern that remains for both non- and induced conditions and decreases with longer inter-lacO distances, in both E. coli and Synechocystis. Repression of Ptrc2O-library promoters with operators out of phase is less efficient in Synechocystis than in E. coli, whereas repression of promoters with lacO in phase is efficient even under induced conditions in Synechocystis. Two well-repressed Ptrc2O promoters were highly active when tested in absence of LacI in Synechocystis. CONCLUSIONS The artificial constitutive promoters herein characterized can be utilized for expression in cyanobacteria, as demonstrated for LacI. The inefficient repression of Ptrc and Ptrc1O-proximal in Synechocystis, as compared to E. coli, may be due to insufficient LacI expression, or differences in RNAP subunits. DNA-looping works as a transcriptional regulation mechanism similarly as in E. coli. DNA-looping contributes strongly to Ptrc2O-library repression in Synechocystis, even though they contain the weakly-repressed primary lacO of Ptrc1O-proximal and relatively low levels of LacI/cell. Hence, Synechocystis RNAP may be more sensitive to DNA-looping than E. coli RNAP, and/or the chromatin torsion resistance could be lower. Two strong and highly repressed Ptrc2O promoters could be used without induction, or together with an unstable LacI.
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Affiliation(s)
| | | | - Peter Lindblad
- Microbial Chemistry, Department of Chemistry-Ångström Laboratory, Science for Life Laboratory, Uppsala University, P,O, Box 523, SE-75120 Uppsala, Sweden.
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