1
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Pichon M, Hollenstein M. Controlled enzymatic synthesis of oligonucleotides. Commun Chem 2024; 7:138. [PMID: 38890393 PMCID: PMC11189433 DOI: 10.1038/s42004-024-01216-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2024] [Accepted: 05/24/2024] [Indexed: 06/20/2024] Open
Abstract
Oligonucleotides are advancing as essential materials for the development of new therapeutics, artificial genes, or in storage of information applications. Hitherto, our capacity to write (i.e., synthesize) oligonucleotides is not as efficient as that to read (i.e., sequencing) DNA/RNA. Alternative, biocatalytic methods for the de novo synthesis of natural or modified oligonucleotides are in dire need to circumvent the limitations of traditional synthetic approaches. This Perspective article summarizes recent progress made in controlled enzymatic synthesis, where temporary blocked nucleotides are incorporated into immobilized primers by polymerases. While robust protocols have been established for DNA, RNA or XNA synthesis is more challenging. Nevertheless, using a suitable combination of protected nucleotides and polymerase has shown promises to produce RNA oligonucleotides even though the production of long DNA/RNA/XNA sequences (>1000 nt) remains challenging. We surmise that merging ligase- and polymerase-based synthesis would help to circumvent the current shortcomings of controlled enzymatic synthesis.
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Affiliation(s)
- Maëva Pichon
- Institut Pasteur, Université Paris Cité, CNRS UMR3523, Department of Structural Biology and Chemistry, Laboratory for Bioorganic Chemistry of Nucleic Acids, 28, Rue du Docteur Roux, 75724, Paris Cedex 15, France
| | - Marcel Hollenstein
- Institut Pasteur, Université Paris Cité, CNRS UMR3523, Department of Structural Biology and Chemistry, Laboratory for Bioorganic Chemistry of Nucleic Acids, 28, Rue du Docteur Roux, 75724, Paris Cedex 15, France.
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2
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Yu M, Tang X, Li Z, Wang W, Wang S, Li M, Yu Q, Xie S, Zuo X, Chen C. High-throughput DNA synthesis for data storage. Chem Soc Rev 2024; 53:4463-4489. [PMID: 38498347 DOI: 10.1039/d3cs00469d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/20/2024]
Abstract
With the explosion of digital world, the dramatically increasing data volume is expected to reach 175 ZB (1 ZB = 1012 GB) in 2025. Storing such huge global data would consume tons of resources. Fortunately, it has been found that the deoxyribonucleic acid (DNA) molecule is the most compact and durable information storage medium in the world so far. Its high coding density and long-term preservation properties make itself one of the best data storage carriers for the future. High-throughput DNA synthesis is a key technology for "DNA data storage", which encodes binary data stream (0/1) into quaternary long DNA sequences consisting of four bases (A/G/C/T). In this review, the workflow of DNA data storage and the basic methods of artificial DNA synthesis technology are outlined first. Then, the technical characteristics of different synthesis methods and the state-of-the-art of representative commercial companies, with a primary focus on silicon chip microarray-based synthesis and novel enzymatic DNA synthesis are presented. Finally, the recent status of DNA storage and new opportunities for future development in the field of high-throughput, large-scale DNA synthesis technology are summarized.
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Affiliation(s)
- Meng Yu
- Institute of Medical Chips, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, 200025, Shanghai, China.
- School of Microelectronics, Shanghai University, 201800, Shanghai, China
- Shanghai Industrial μTechnology Research Institute, 201800, Shanghai, China
| | - Xiaohui Tang
- Institute of Medical Chips, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, 200025, Shanghai, China.
- Shanghai Industrial μTechnology Research Institute, 201800, Shanghai, China
| | - Zhenhua Li
- Institute of Medical Chips, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, 200025, Shanghai, China.
- Shanghai Industrial μTechnology Research Institute, 201800, Shanghai, China
| | - Weidong Wang
- Shanghai Industrial μTechnology Research Institute, 201800, Shanghai, China
| | - Shaopeng Wang
- Institute of Molecular Medicine, Renji Hospital, School of Medicine, Shanghai Jiao Tong University, 200127, Shanghai, China.
| | - Min Li
- Institute of Molecular Medicine, Renji Hospital, School of Medicine, Shanghai Jiao Tong University, 200127, Shanghai, China.
| | - Qiuliyang Yu
- Shenzhen Key Laboratory for the Intelligent Microbial Manufacturing of Medicines, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, China
| | - Sijia Xie
- Institute of Medical Chips, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, 200025, Shanghai, China.
- School of Microelectronics, Shanghai University, 201800, Shanghai, China
- Shanghai Industrial μTechnology Research Institute, 201800, Shanghai, China
| | - Xiaolei Zuo
- Institute of Molecular Medicine, Renji Hospital, School of Medicine, Shanghai Jiao Tong University, 200127, Shanghai, China.
| | - Chang Chen
- Institute of Medical Chips, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, 200025, Shanghai, China.
- School of Microelectronics, Shanghai University, 201800, Shanghai, China
- Shanghai Industrial μTechnology Research Institute, 201800, Shanghai, China
- State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 200050, Shanghai, China
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3
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Simmons BL, McDonald ND, Robinett NG. Assessment of enzymatically synthesized DNA for gene assembly. Front Bioeng Biotechnol 2023; 11:1208784. [PMID: 37476479 PMCID: PMC10354541 DOI: 10.3389/fbioe.2023.1208784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Accepted: 06/20/2023] [Indexed: 07/22/2023] Open
Abstract
Phosphoramidite chemical DNA synthesis technology is utilized for creating de novo ssDNA building blocks and is widely used by commercial vendors. Recent advances in enzymatic DNA synthesis (EDS), including engineered enzymes and reversibly terminated nucleotides, bring EDS technology into competition with traditional chemical methods. In this short study, we evaluate oligos produced using a benchtop EDS instrument alongside chemically produced commercial oligonucleotides to assemble a synthetic gene encoding green fluorescent protein (GFP). While enzymatic synthesis produced lower concentrations of individual oligonucleotides, these were available in half the time of commercially produced oligonucleotides and were sufficient to assemble functional GFP sequences without producing hazardous organic chemical waste.
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Affiliation(s)
- Brooke L. Simmons
- U.S. Army Combat Capabilities Development Command (DEVCOM) Chemical Biological Center, Gunpowder, MD, United States
- Oak Ridge Institute for Science and Education (ORISE), Oak Ridge, TN, United States
| | - Nathan D. McDonald
- U.S. Army Combat Capabilities Development Command (DEVCOM) Chemical Biological Center, Gunpowder, MD, United States
| | - Natalie G. Robinett
- U.S. Army Combat Capabilities Development Command (DEVCOM) Chemical Biological Center, Gunpowder, MD, United States
- Excet, Inc., Springfield, VA, United States
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Debon A, Siirola E, Snajdrova R. Enzymatic Bioconjugation: A Perspective from the Pharmaceutical Industry. JACS AU 2023; 3:1267-1283. [PMID: 37234110 PMCID: PMC10207132 DOI: 10.1021/jacsau.2c00617] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 01/10/2023] [Accepted: 01/10/2023] [Indexed: 05/27/2023]
Abstract
Enzymes have firmly established themselves as bespoke catalysts for small molecule transformations in the pharmaceutical industry, from early research and development stages to large-scale production. In principle, their exquisite selectivity and rate acceleration can also be leveraged for modifying macromolecules to form bioconjugates. However, available catalysts face stiff competition from other bioorthogonal chemistries. In this Perspective, we seek to illuminate applications of enzymatic bioconjugation in the face of an expanding palette of new drug modalities. With these applications, we wish to highlight some examples of current successes and pitfalls of using enzymes for bioconjugation along the pipeline and try to illustrate opportunities for further development.
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Affiliation(s)
- Aaron Debon
- Global
Discovery Chemistry, Novartis Institute
for Biomedical Research, Basel 4108, Switzerland
| | - Elina Siirola
- Global
Discovery Chemistry, Novartis Institute
for Biomedical Research, Basel 4108, Switzerland
| | - Radka Snajdrova
- Global
Discovery Chemistry, Novartis Institute
for Biomedical Research, Basel 4108, Switzerland
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5
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Torres-Huerta AL, Antonio-Pérez A, García-Huante Y, Alcázar-Ramírez NJ, Rueda-Silva JC. Biomolecule-Based Optical Metamaterials: Design and Applications. BIOSENSORS 2022; 12:962. [PMID: 36354471 PMCID: PMC9688573 DOI: 10.3390/bios12110962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 10/21/2022] [Accepted: 10/22/2022] [Indexed: 06/16/2023]
Abstract
Metamaterials are broadly defined as artificial, electromagnetically homogeneous structures that exhibit unusual physical properties that are not present in nature. They possess extraordinary capabilities to bend electromagnetic waves. Their size, shape and composition can be engineered to modify their characteristics, such as iridescence, color shift, absorbance at different wavelengths, etc., and harness them as biosensors. Metamaterial construction from biological sources such as carbohydrates, proteins and nucleic acids represents a low-cost alternative, rendering high quantities and yields. In addition, the malleability of these biomaterials makes it possible to fabricate an endless number of structured materials such as composited nanoparticles, biofilms, nanofibers, quantum dots, and many others, with very specific, invaluable and tremendously useful optical characteristics. The intrinsic characteristics observed in biomaterials make them suitable for biomedical applications. This review addresses the optical characteristics of metamaterials obtained from the major macromolecules found in nature: carbohydrates, proteins and DNA, highlighting their biosensor field use, and pointing out their physical properties and production paths.
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Affiliation(s)
- Ana Laura Torres-Huerta
- Escuela de Ingeniería y Ciencias, Tecnológico de Monterrey, Campus Estado de México, Av. Lago de Guadalupe KM 3.5, Margarita Maza de Juárez, Cd. López Mateos, Atizapán de Zaragoza 52926, Mexico
| | - Aurora Antonio-Pérez
- Escuela de Ingeniería y Ciencias, Tecnológico de Monterrey, Campus Estado de México, Av. Lago de Guadalupe KM 3.5, Margarita Maza de Juárez, Cd. López Mateos, Atizapán de Zaragoza 52926, Mexico
| | - Yolanda García-Huante
- Departamento de Ciencias Básicas, Unidad Profesional Interdisciplinaria en Ingeniería y Tecnologías Avanzadas, Instituto Politécnico Nacional (UPIITA-IPN), Mexico City 07340, Mexico
| | - Nayelhi Julieta Alcázar-Ramírez
- Escuela de Ingeniería y Ciencias, Tecnológico de Monterrey, Campus Estado de México, Av. Lago de Guadalupe KM 3.5, Margarita Maza de Juárez, Cd. López Mateos, Atizapán de Zaragoza 52926, Mexico
| | - Juan Carlos Rueda-Silva
- Escuela de Ingeniería y Ciencias, Tecnológico de Monterrey, Campus Estado de México, Av. Lago de Guadalupe KM 3.5, Margarita Maza de Juárez, Cd. López Mateos, Atizapán de Zaragoza 52926, Mexico
- Department of Genetics, University of Cambridge, Cambridge CB2 3EH, UK
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6
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Song LF, Deng ZH, Gong ZY, Li LL, Li BZ. Large-Scale de novo Oligonucleotide Synthesis for Whole-Genome Synthesis and Data Storage: Challenges and Opportunities. Front Bioeng Biotechnol 2021; 9:689797. [PMID: 34239862 PMCID: PMC8258115 DOI: 10.3389/fbioe.2021.689797] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 05/27/2021] [Indexed: 11/13/2022] Open
Abstract
Over the past decades, remarkable progress on phosphoramidite chemistry-based large-scale de novo oligonucleotide synthesis has been achieved, enabling numerous novel and exciting applications. Among them, de novo genome synthesis and DNA data storage are striking. However, to make these two applications more practical, the synthesis length, speed, cost, and throughput require vast improvements, which is a challenge to be met by the phosphoramidite chemistry. Harnessing the power of enzymes, the recently emerged enzymatic methods provide a competitive route to overcome this challenge. In this review, we first summarize the status of large-scale oligonucleotide synthesis technologies including the basic methodology and large-scale synthesis approaches, with special focus on the emerging enzymatic methods. Afterward, we discuss the opportunities and challenges of large-scale oligonucleotide synthesis on de novo genome synthesis and DNA data storage respectively.
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Affiliation(s)
- Li-Fu Song
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
- School of Chemical Engineering and Technology, Tianjin University, Tianjin, China
| | - Zheng-Hua Deng
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
- School of Chemical Engineering and Technology, Tianjin University, Tianjin, China
| | - Zi-Yi Gong
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
- School of Chemical Engineering and Technology, Tianjin University, Tianjin, China
| | - Lu-Lu Li
- LC-BIO Technologies Co., Ltd., Hangzhou, China
| | - Bing-Zhi Li
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
- School of Chemical Engineering and Technology, Tianjin University, Tianjin, China
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7
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Yoo E, Choe D, Shin J, Cho S, Cho BK. Mini review: Enzyme-based DNA synthesis and selective retrieval for data storage. Comput Struct Biotechnol J 2021; 19:2468-2476. [PMID: 34025937 PMCID: PMC8113751 DOI: 10.1016/j.csbj.2021.04.057] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 04/20/2021] [Accepted: 04/22/2021] [Indexed: 11/26/2022] Open
Abstract
The market for using and storing digital data is growing, with DNA synthesis emerging as an efficient way to store massive amounts of data. Storing information in DNA mainly consists of two steps: data writing and reading. The writing step requires encoding data in DNA, building one nucleotide at a time as a form of single-stranded DNA (ssDNA). Once the data needs to be read, the target DNA is selectively retrieved and sequenced, which will also be in the form of an ssDNA. Recently, enzyme-based DNA synthesis is emerging as a new method to be a breakthrough on behalf of decades-old chemical synthesis. A few enzymatic methods have been presented for data memory, including the use of terminal deoxynucleotidyl transferase. Besides, enzyme-based amplification or denaturation of the target strand into ssDNA provides selective access to the desired dataset. In this review, we summarize diverse enzymatic methods for either synthesizing ssDNA or retrieving the data-containing DNA.
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Affiliation(s)
- Eojin Yoo
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea
| | - Donghui Choe
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea
| | - Jongoh Shin
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea
| | - Suhyung Cho
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea.,Innovative Biomaterials Research Center, KI for the BioCentury, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea
| | - Byung-Kwan Cho
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea.,Innovative Biomaterials Research Center, KI for the BioCentury, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea
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8
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Hoff K, Halpain M, Garbagnati G, Edwards JS, Zhou W. Enzymatic Synthesis of Designer DNA Using Cyclic Reversible Termination and a Universal Template. ACS Synth Biol 2020; 9:283-293. [PMID: 31895546 DOI: 10.1021/acssynbio.9b00315] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Phosphoramidite chemistry remains the industry standard for DNA synthesis despite significant limitations on the length and yield of the oligonucleotide, time restrictions, and hazardous waste production. Herein, we demonstrate the synthesis of single-stranded oligos on a solid surface by DNA polymerases and reverse transcriptases. We report the extension of surface-bound oligonucleotides enabled by transient hybridization of as few as two bases to a neighboring strand. When multiple hybridization structures are possible, each templating a different base, a DNA polymerase or reverse transcriptase can extend the oligonucleotide with any of the complementary bases. Therefore, the sequence of the newly synthesized fragment can be controlled by adding only the desired base as a substrate to the reaction solution. We used this enzymatic approach to synthesize a 20 base oligonucleotide by incorporating reversible terminator dNTPs through a two-step cyclic reversible termination process with a corrected stepwise efficiency over 98%. In our approach, a nascent DNA strand that serves as both primer and template is extended through polymerase-controlled sequential addition of 3'-reversibly blocked nucleotides followed by subsequent cleavage of the 3'-capping group. This process enables oligonucleotide synthesis in an environment not permitted by traditional phosphoramidite methods, eliminates the need for hazardous chemicals, has the potential to provide faster and higher yield results, and synthesizes DNA on a solid support with a free 3' end.
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Affiliation(s)
- Kendall Hoff
- Department of Advanced Research and Development, Centrillion Biosciences, Palo Alto, California 94303, United States
| | - Michelle Halpain
- Department of Advanced Research and Development, Centrillion Biosciences, Palo Alto, California 94303, United States
| | - Giancarlo Garbagnati
- Department of Advanced Research and Development, Centrillion Biosciences, Palo Alto, California 94303, United States
| | - Jeremy S. Edwards
- Department of Advanced Research and Development, Centrillion Biosciences, Palo Alto, California 94303, United States
- Chemistry and Chemical Biology and Chemical and Biological Engineering, University of New Mexico, Albuquerque, New Mexico 87131, United States
- Internal Medicine, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131, United States
- University of New Mexico Comprehensive Cancer Center, Albuquerque, New Mexico 87131, United States
| | - Wei Zhou
- Department of Advanced Research and Development, Centrillion Biosciences, Palo Alto, California 94303, United States
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Enhancing Terminal Deoxynucleotidyl Transferase Activity on Substrates with 3' Terminal Structures for Enzymatic De Novo DNA Synthesis. Genes (Basel) 2020; 11:genes11010102. [PMID: 31963235 PMCID: PMC7016565 DOI: 10.3390/genes11010102] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Revised: 12/31/2019] [Accepted: 01/07/2020] [Indexed: 01/13/2023] Open
Abstract
Enzymatic oligonucleotide synthesis methods based on the template-independent polymerase terminal deoxynucleotidyl transferase (TdT) promise to enable the de novo synthesis of long oligonucleotides under mild, aqueous conditions. Intermediates with a 3′ terminal structure (hairpins) will inevitably arise during synthesis, but TdT has poor activity on these structured substrates, limiting its usefulness for oligonucleotide synthesis. Here, we described two parallel efforts to improve the activity of TdT on hairpins: (1) optimization of the concentrations of the divalent cation cofactors and (2) engineering TdT for enhanced thermostability, enabling reactions at elevated temperatures. By combining both of these improvements, we obtained a ~10-fold increase in the elongation rate of a guanine-cytosine hairpin.
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10
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Sarac I, Hollenstein M. Terminal Deoxynucleotidyl Transferase in the Synthesis and Modification of Nucleic Acids. Chembiochem 2019; 20:860-871. [PMID: 30451377 DOI: 10.1002/cbic.201800658] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2018] [Indexed: 12/26/2022]
Abstract
The terminal deoxynucleotidyl transferase (TdT) belongs to the X family of DNA polymerases. This unusual polymerase catalyzes the template-independent addition of random nucleotides on 3'-overhangs during V(D)J recombination. The biological function and intrinsic biochemical properties of the TdT have spurred the development of numerous oligonucleotide-based tools and methods, especially if combined with modified nucleoside triphosphates. Herein, we summarize the different applications stemming from the incorporation of modified nucleotides by the TdT. The structural, mechanistic, and biochemical properties of this polymerase are also discussed.
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Affiliation(s)
- Ivo Sarac
- Laboratory for Bioorganic Chemistry of Nucleic Acids, Department of Structural Biology and Chemistry, Institut Pasteur, CNRS UMR3523, 28, rue du Docteur Roux, 75724, Paris Cedex 15, France
| | - Marcel Hollenstein
- Laboratory for Bioorganic Chemistry of Nucleic Acids, Department of Structural Biology and Chemistry, Institut Pasteur, CNRS UMR3523, 28, rue du Docteur Roux, 75724, Paris Cedex 15, France
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11
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De novo DNA synthesis using polymerase-nucleotide conjugates. Nat Biotechnol 2018; 36:645-650. [PMID: 29912208 DOI: 10.1038/nbt.4173] [Citation(s) in RCA: 131] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Accepted: 05/22/2018] [Indexed: 01/02/2023]
Abstract
Oligonucleotides are almost exclusively synthesized using the nucleoside phosphoramidite method, even though it is limited to the direct synthesis of ∼200 mers and produces hazardous waste. Here, we describe an oligonucleotide synthesis strategy that uses the template-independent polymerase terminal deoxynucleotidyl transferase (TdT). Each TdT molecule is conjugated to a single deoxyribonucleoside triphosphate (dNTP) molecule that it can incorporate into a primer. After incorporation of the tethered dNTP, the 3' end of the primer remains covalently bound to TdT and is inaccessible to other TdT-dNTP molecules. Cleaving the linkage between TdT and the incorporated nucleotide releases the primer and allows subsequent extension. We demonstrate that TdT-dNTP conjugates can quantitatively extend a primer by a single nucleotide in 10-20 s, and that the scheme can be iterated to write a defined sequence. This approach may form the basis of an enzymatic oligonucleotide synthesizer.
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