1
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Yap ZL, Rahman ASMZ, Hogan AM, Levin DB, Cardona ST. A CRISPR-Cas-associated transposon system for genome editing in Burkholderia cepacia complex species. Appl Environ Microbiol 2024; 90:e0069924. [PMID: 38869300 PMCID: PMC11267881 DOI: 10.1128/aem.00699-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2024] [Accepted: 05/20/2024] [Indexed: 06/14/2024] Open
Abstract
Genome editing in non-model bacteria is important to understand gene-to-function links that may differ from those of model microorganisms. Although species of the Burkholderia cepacia complex (Bcc) have great biotechnological capacities, the limited genetic tools available to understand and mitigate their pathogenic potential hamper their utilization in industrial applications. To broaden the genetic tools available for Bcc species, we developed RhaCAST, a targeted DNA insertion platform based on a CRISPR-associated transposase driven by a rhamnose-inducible promoter. We demonstrated the utility of the system for targeted insertional mutagenesis in the Bcc strains B. cenocepacia K56-2 and Burkholderia multivorans ATCC17616. We showed that the RhaCAST system can be used for loss- and gain-of-function applications. Importantly, the selection marker could be excised and reused to allow iterative genetic manipulation. The RhaCAST system is faster, easier, and more adaptable than previous insertional mutagenesis tools available for Bcc species and may be used to disrupt pathogenicity elements and insert relevant genetic modules, enabling Bcc biotechnological applications. IMPORTANCE Species of the Burkholderia cepacia complex (Bcc) have great biotechnological potential but are also opportunistic pathogens. Genetic manipulation of Bcc species is necessary to understand gene-to-function links. However, limited genetic tools are available to manipulate Bcc, hindering our understanding of their pathogenic traits and their potential in biotechnological applications. We developed a genetic tool based on CRISPR-associated transposase to increase the genetic tools available for Bcc species. The genetic tool we developed in this study can be used for loss and gain of function in Bcc species. The significance of our work is in expanding currently available tools to manipulate Bcc.
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Affiliation(s)
- Zhong Ling Yap
- Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada
| | | | - Andrew M. Hogan
- Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada
| | - David B. Levin
- Department of Biosystems Engineering, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Silvia T. Cardona
- Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada
- Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Manitoba, Canada
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2
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Tenjo-Castaño F, Sofos N, Stutzke LS, Temperini P, Fuglsang A, Pape T, Mesa P, Montoya G. Conformational landscape of the type V-K CRISPR-associated transposon integration assembly. Mol Cell 2024; 84:2353-2367.e5. [PMID: 38834066 DOI: 10.1016/j.molcel.2024.05.005] [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: 12/08/2023] [Revised: 03/11/2024] [Accepted: 05/07/2024] [Indexed: 06/06/2024]
Abstract
CRISPR-associated transposons (CASTs) are mobile genetic elements that co-opt CRISPR-Cas systems for RNA-guided DNA transposition. CASTs integrate large DNA cargos into the attachment (att) site independently of homology-directed repair and thus hold promise for eukaryotic genome engineering. However, the functional diversity and complexity of CASTs hinder an understanding of their mechanisms. Here, we present the high-resolution cryoelectron microscopy (cryo-EM) structure of the reconstituted ∼1 MDa post-transposition complex of the type V-K CAST, together with different assembly intermediates and diverse TnsC filament lengths, thus enabling the recapitulation of the integration complex formation. The results of mutagenesis experiments probing the roles of specific residues and TnsB-binding sites show that transposition activity can be enhanced and suggest that the distance between the PAM and att sites is determined by the lengths of the TnsB C terminus and the TnsC filament. This singular model of RNA-guided transposition provides a foundation for repurposing the system for genome-editing applications.
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Affiliation(s)
- Francisco Tenjo-Castaño
- Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
| | - Nicholas Sofos
- Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
| | - Luisa S Stutzke
- Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
| | - Piero Temperini
- Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
| | - Anders Fuglsang
- Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
| | - Tillmann Pape
- Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark; Core Facility for Integrated Microscopy (CFIM), Faculty of Health and Medical Sciences University of Copenhagen; Blegdamsvej 3B, DK-2200 Copenhagen, Denmark
| | - Pablo Mesa
- Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
| | - Guillermo Montoya
- Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark.
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3
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Villiger L, Joung J, Koblan L, Weissman J, Abudayyeh OO, Gootenberg JS. CRISPR technologies for genome, epigenome and transcriptome editing. Nat Rev Mol Cell Biol 2024; 25:464-487. [PMID: 38308006 DOI: 10.1038/s41580-023-00697-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/18/2023] [Indexed: 02/04/2024]
Abstract
Our ability to edit genomes lags behind our capacity to sequence them, but the growing understanding of CRISPR biology and its application to genome, epigenome and transcriptome engineering is narrowing this gap. In this Review, we discuss recent developments of various CRISPR-based systems that can transiently or permanently modify the genome and the transcriptome. The discovery of further CRISPR enzymes and systems through functional metagenomics has meaningfully broadened the applicability of CRISPR-based editing. Engineered Cas variants offer diverse capabilities such as base editing, prime editing, gene insertion and gene regulation, thereby providing a panoply of tools for the scientific community. We highlight the strengths and weaknesses of current CRISPR tools, considering their efficiency, precision, specificity, reliance on cellular DNA repair mechanisms and their applications in both fundamental biology and therapeutics. Finally, we discuss ongoing clinical trials that illustrate the potential impact of CRISPR systems on human health.
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Affiliation(s)
- Lukas Villiger
- McGovern Institute for Brain Research, Massachusetts Institute of Technology Cambridge, Cambridge, MA, USA
| | - Julia Joung
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Luke Koblan
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Jonathan Weissman
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA
- David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Omar O Abudayyeh
- McGovern Institute for Brain Research, Massachusetts Institute of Technology Cambridge, Cambridge, MA, USA.
| | - Jonathan S Gootenberg
- McGovern Institute for Brain Research, Massachusetts Institute of Technology Cambridge, Cambridge, MA, USA.
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4
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de la Gándara Á, Spínola-Amilibia M, Araújo-Bazán L, Núñez-Ramírez R, Berger JM, Arias-Palomo E. Molecular basis for transposase activation by a dedicated AAA+ ATPase. Nature 2024; 630:1003-1011. [PMID: 38926614 PMCID: PMC11208146 DOI: 10.1038/s41586-024-07550-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Accepted: 05/09/2024] [Indexed: 06/28/2024]
Abstract
Transposases drive chromosomal rearrangements and the dissemination of drug-resistance genes and toxins1-3. Although some transposases act alone, many rely on dedicated AAA+ ATPase subunits that regulate site selectivity and catalytic function through poorly understood mechanisms. Using IS21 as a model transposase system, we show how an ATPase regulator uses nucleotide-controlled assembly and DNA deformation to enable structure-based site selectivity, transposase recruitment, and activation and integration. Solution and cryogenic electron microscopy studies show that the IstB ATPase self-assembles into an autoinhibited pentamer of dimers that tightly curves target DNA into a half-coil. Two of these decamers dimerize, which stabilizes the target nucleic acid into a kinked S-shaped configuration that engages the IstA transposase at the interface between the two IstB oligomers to form an approximately 1 MDa transpososome complex. Specific interactions stimulate regulator ATPase activity and trigger a large conformational change on the transposase that positions the catalytic site to perform DNA strand transfer. These studies help explain how AAA+ ATPase regulators-which are used by classical transposition systems such as Tn7, Mu and CRISPR-associated elements-can remodel their substrate DNA and cognate transposases to promote function.
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Affiliation(s)
| | | | - Lidia Araújo-Bazán
- Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, Spain
| | | | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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5
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Chang CW, Truong VA, Pham NN, Hu YC. RNA-guided genome engineering: paradigm shift towards transposons. Trends Biotechnol 2024:S0167-7799(24)00035-0. [PMID: 38443218 DOI: 10.1016/j.tibtech.2024.02.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2023] [Revised: 02/05/2024] [Accepted: 02/06/2024] [Indexed: 03/07/2024]
Abstract
CRISPR-Cas systems revolutionized the genome engineering field but need to induce double-strand breaks (DSBs) and may be difficult to deliver due to their large protein size. Tn7-like transposons such as CRISPR-associated transposons (CASTs) can be repurposed for RNA-guided DSB-free integration, and obligate mobile element guided activity (OMEGA) proteins of the IS200/IS605 transposon family have been developed as hypercompact RNA-guided genome editing tools. CASTs and OMEGA are exciting, innovative genome engineering tools that can improve the precision and efficiency of editing. This review explores the recent developments and uses of CASTs and OMEGA in genome editing across prokaryotic and eukaryotic cells. The pros and cons of these transposon-based systems are deliberated in comparison to other CRISPR systems.
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Affiliation(s)
- Chin-Wei Chang
- Department of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan
| | - Vy Anh Truong
- Department of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan
| | - Nam Ngoc Pham
- Department of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan
| | - Yu-Chen Hu
- Department of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan; Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 300, Taiwan.
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6
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Schmitz M, Querques I. DNA on the move: mechanisms, functions and applications of transposable elements. FEBS Open Bio 2024; 14:13-22. [PMID: 38041553 PMCID: PMC10761935 DOI: 10.1002/2211-5463.13743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 10/24/2023] [Accepted: 11/30/2023] [Indexed: 12/03/2023] Open
Abstract
Transposons are mobile genetic elements that have invaded all domains of life by moving between and within their host genomes. Due to their mobility (or transposition), transposons facilitate horizontal gene transfer in bacteria and foster the evolution of new molecular functions in prokaryotes and eukaryotes. As transposition can lead to detrimental genomic rearrangements, organisms have evolved a multitude of molecular strategies to control transposons, including genome defense mechanisms provided by CRISPR-Cas systems. Apart from their biological impacts on genomes, DNA transposons have been leveraged as efficient gene insertion vectors in basic research, transgenesis and gene therapy. However, the close to random insertion profile of transposon-based tools limits their programmability and safety. Despite recent advances brought by the development of CRISPR-associated genome editing nucleases, a strategy for efficient insertion of large, multi-kilobase transgenes at user-defined genomic sites is currently challenging. The discovery and experimental characterization of bacterial CRISPR-associated transposons (CASTs) led to the attractive hypothesis that these systems could be repurposed as programmable, site-specific gene integration technologies. Here, we provide a broad overview of the molecular mechanisms underpinning DNA transposition and of its biological and technological impact. The second focus of the article is to describe recent mechanistic and functional analyses of CAST transposition. Finally, current challenges and desired future advances of CAST-based genome engineering applications are briefly discussed.
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Affiliation(s)
| | - Irma Querques
- Department of BiochemistryUniversity of ZurichSwitzerland
- Max Perutz Labs, Vienna Biocenter Campus (VBC)Austria
- Department of Structural and Computational Biology, Center for Molecular BiologyUniversity of ViennaAustria
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7
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Tou CJ, Kleinstiver BP. Recent Advances in Double-Strand Break-Free Kilobase-Scale Genome Editing Technologies. Biochemistry 2023; 62:3493-3499. [PMID: 36049184 PMCID: PMC10239562 DOI: 10.1021/acs.biochem.2c00311] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Genome editing approaches have transformed the ability to make user-defined changes to genomes in both ex vivo and in vivo contexts. Despite the abundant development of technologies that permit the installation of nucleotide-level changes, until recently, larger-scale sequence edits via technologies independent of DNA double-strand breaks (DSBs) had remained less explored. Here, we review recent advances toward DSB-free technologies that enable kilobase-scale modifications including insertions, deletions, inversions, replacements, and others. These technologies provide new capabilities for users, while offering hope for the simplification of putative therapeutic strategies by moving away from small mutation-specific edits and toward more generalizable kilobase-scale approaches.
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Affiliation(s)
- Connor J. Tou
- Biological Engineering Program, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Pathology, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Benjamin P. Kleinstiver
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Pathology, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Pathology, Harvard Medical School, Boston, MA, 02115, USA
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8
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Dhingra Y, Sashital DG. A tool for more specific DNA integration. Science 2023; 382:768-769. [PMID: 37972178 DOI: 10.1126/science.adl0863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023]
Abstract
The efficiency of targeted DNA insertion by CRISPR transposons is improved.
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Affiliation(s)
- Yukti Dhingra
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
| | - Dipali G Sashital
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
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9
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George JT, Acree C, Park JU, Kong M, Wiegand T, Pignot YL, Kellogg EH, Greene EC, Sternberg SH. Mechanism of target site selection by type V-K CRISPR-associated transposases. Science 2023; 382:eadj8543. [PMID: 37972161 PMCID: PMC10771339 DOI: 10.1126/science.adj8543] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Accepted: 09/23/2023] [Indexed: 11/19/2023]
Abstract
CRISPR-associated transposases (CASTs) repurpose nuclease-deficient CRISPR effectors to catalyze RNA-guided transposition of large genetic payloads. Type V-K CASTs offer potential technology advantages but lack accuracy, and the molecular basis for this drawback has remained elusive. Here, we reveal that type V-K CASTs maintain an RNA-independent, "untargeted" transposition pathway alongside RNA-dependent integration, driven by the local availability of TnsC filaments. Using cryo-electron microscopy, single-molecule experiments, and high-throughput sequencing, we found that a minimal, CRISPR-less transpososome preferentially directs untargeted integration at AT-rich sites, with additional local specificity imparted by TnsB. By exploiting this knowledge, we suppressed untargeted transposition and increased type V-K CAST specificity up to 98.1% in cells without compromising on-target integration efficiency. These findings will inform further engineering of CAST systems for accurate, kilobase-scale genome engineering applications.
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Affiliation(s)
- Jerrin Thomas George
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Christopher Acree
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Jung-Un Park
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Muwen Kong
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Tanner Wiegand
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Yanis Luca Pignot
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Elizabeth H. Kellogg
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Eric C. Greene
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Samuel H. Sternberg
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
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10
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Wang S, Gabel C, Siddique R, Klose T, Chang L. Molecular mechanism for Tn7-like transposon recruitment by a type I-B CRISPR effector. Cell 2023; 186:4204-4215.e19. [PMID: 37557170 PMCID: PMC11027886 DOI: 10.1016/j.cell.2023.07.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 04/23/2023] [Accepted: 07/10/2023] [Indexed: 08/11/2023]
Abstract
Tn7-like transposons have co-opted CRISPR-Cas systems to facilitate the movement of their own DNA. These CRISPR-associated transposons (CASTs) are promising tools for programmable gene knockin. A key feature of CASTs is their ability to recruit Tn7-like transposons to nuclease-deficient CRISPR effectors. However, how Tn7-like transposons are recruited by diverse CRISPR effectors remains poorly understood. Here, we present the cryo-EM structure of a recruitment complex comprising the Cascade complex, TniQ, TnsC, and the target DNA in the type I-B CAST from Peltigera membranacea cyanobiont 210A. Target DNA recognition by Cascade induces conformational changes in Cas6 and primes TniQ recruitment through its C-terminal domain. The N-terminal domain of TniQ is bound to the seam region of the TnsC spiral heptamer. Our findings provide insights into the diverse mechanisms for the recruitment of Tn7-like transposons to CRISPR effectors and will aid in the development of CASTs as gene knockin tools.
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Affiliation(s)
- Shukun Wang
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
| | - Clinton Gabel
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
| | - Romana Siddique
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
| | - Thomas Klose
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
| | - Leifu Chang
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Cancer Research, Purdue University, West Lafayette, IN 47907, USA.
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11
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George JT, Acree C, Park JU, Kong M, Wiegand T, Pignot YL, Kellogg EH, Greene EC, Sternberg SH. Mechanism of target site selection by type V-K CRISPR-associated transposases. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.14.548620. [PMID: 37503092 PMCID: PMC10370016 DOI: 10.1101/2023.07.14.548620] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Unlike canonical CRISPR-Cas systems that rely on RNA-guided nucleases for target cleavage, CRISPR-associated transposases (CASTs) repurpose nuclease-deficient CRISPR effectors to facilitate RNA-guided transposition of large genetic payloads. Type V-K CASTs offer several potential upsides for genome engineering, due to their compact size, easy programmability, and unidirectional integration. However, these systems are substantially less accurate than type I-F CASTs, and the molecular basis for this difference has remained elusive. Here we reveal that type V-K CASTs undergo two distinct mobilization pathways with remarkably different specificities: RNA-dependent and RNA-independent transposition. Whereas RNA-dependent transposition relies on Cas12k for accurate target selection, RNA-independent integration events are untargeted and primarily driven by the local availability of TnsC filaments. The cryo-EM structure of the untargeted complex reveals a TnsB-TnsC-TniQ transpososome that encompasses two turns of a TnsC filament and otherwise resembles major architectural aspects of the Cas12k-containing transpososome. Using single-molecule experiments and genome-wide meta-analyses, we found that AT-rich sites are preferred substrates for untargeted transposition and that the TnsB transposase also imparts local specificity, which collectively determine the precise insertion site. Knowledge of these motifs allowed us to direct untargeted transposition events to specific hotspot regions of a plasmid. Finally, by exploiting TnsB's preference for on-target integration and modulating the availability of TnsC, we suppressed RNA-independent transposition events and increased type V-K CAST specificity up to 98.1%, without compromising the efficiency of on-target integration. Collectively, our results reveal the importance of dissecting target site selection mechanisms and highlight new opportunities to leverage CAST systems for accurate, kilobase-scale genome engineering applications.
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Affiliation(s)
- Jerrin Thomas George
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Christopher Acree
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
- Present address: Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37212, USA
| | - Jung-Un Park
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
- Future address: Department of Structural Biology. St Jude Children’s Research Hospital, Memphis, TN 38105, USA
| | - Muwen Kong
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Tanner Wiegand
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Yanis Luca Pignot
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
- Present address: Department of Biochemistry, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Elizabeth H. Kellogg
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
- Future address: Department of Structural Biology. St Jude Children’s Research Hospital, Memphis, TN 38105, USA
| | - Eric C. Greene
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Samuel H. Sternberg
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
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12
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Trujillo Rodríguez L, Ellington AJ, Reisch CR, Chevrette MG. CRISPR-Associated Transposase for Targeted Mutagenesis in Diverse Proteobacteria. ACS Synth Biol 2023. [PMID: 37368499 PMCID: PMC10367135 DOI: 10.1021/acssynbio.3c00065] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/29/2023]
Abstract
Genome editing tools, through the disruption of an organism's native genetic material or the introduction of non-native DNA, facilitate functional investigations to link genotypes to phenotypes. Transposons have been instrumental genetic tools in microbiology, enabling genome-wide, randomized disruption of genes and insertions of new genetic elements. Due to this randomness, identifying and isolating particular transposon mutants (i.e., those with modifications at a genetic locus of interest) can be laborious, often requiring one to sift through hundreds or thousands of mutants. Programmable, site-specific targeting of transposons became possible with recently described CRISPR-associated transposase (CASTs) systems, allowing the streamlined recovery of desired mutants in a single step. Like other CRISPR-derived systems, CASTs can be programmed by guide-RNA that is transcribed from short DNA sequence(s). Here, we describe a CAST system and demonstrate its function in bacteria from three classes of Proteobacteria. A dual plasmid strategy is demonstrated: (i) CAST genes are expressed from a broad-host-range replicative plasmid and (ii) guide-RNA and transposon are encoded on a high-copy, suicidal pUC plasmid. Using our CAST system, single-gene disruptions were performed with on-target efficiencies approaching 100% in Beta- and Gammaproteobacteria (Burkholderia thailandensis and Pseudomonas putida, respectively). We also report a peak efficiency of 45% in the Alphaproteobacterium Agrobacterium fabrum. In B. thailandensis, we performed simultaneous co-integration of transposons at two different target sites, demonstrating CAST's utility in multilocus strategies. The CAST system is also capable of high-efficiency large transposon insertion totaling over 11 kbp in all three bacteria tested. Lastly, the dual plasmid system allowed for iterative transposon mutagenesis in all three bacteria without loss of efficiency. Given these iterative capabilities and large payload capacity, this system will be helpful for genome engineering experiments across several fields of research.
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Affiliation(s)
- Lidimarie Trujillo Rodríguez
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611, United States
| | - Adam J Ellington
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611, United States
| | - Christopher R Reisch
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611, United States
| | - Marc G Chevrette
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611, United States
- University of Florida Genetics Institute, Gainesville, Florida 32610, United States
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13
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Zeng T, Yin J, Liu Z, Li Z, Zhang Y, Lv Y, Lu ML, Luo M, Chen M, Xiao Y. Mechanistic insights into transposon cleavage and integration by TnsB of ShCAST system. Cell Rep 2023; 42:112698. [PMID: 37379212 DOI: 10.1016/j.celrep.2023.112698] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 04/02/2023] [Accepted: 06/09/2023] [Indexed: 06/30/2023] Open
Abstract
The type V-K CRISPR-associated transposons (CASTs) allow RNA-guided DNA integration and have great potential as a programmable site-specific gene insertion tool. Although all core components have been independently characterized structurally, the mechanism of how the transposase TnsB associates with AAA+ ATPase TnsC and catalyzes donor DNA cleavage and integration remains ambiguous. In this study, we demonstrate that TniQ-dCas9 fusion can direct site-specific transposition by TnsB/TnsC in ShCAST. TnsB is a 3'-5' exonuclease that specifically cleaves donor DNA at the end of the terminal repeats and integrates the left end prior to the right end. The nucleotide preference and the cleavage site of TnsB are markedly different from those of the well-documented MuA. We also find that TnsB/TnsC association is enhanced in a half-integration state. Overall, our results provide valuable insights into the mechanism and application expansion of CRISPR-mediated site-specific transposition by TnsB/TnsC.
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Affiliation(s)
- Ting Zeng
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China; Department of Pharmacology, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China
| | - Jie Yin
- Department of Biochemistry, School of Life Science and Technology, China Pharmaceutical University, Nanjing 210009, China
| | - Ziwen Liu
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China; Department of Pharmacology, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China
| | - Zhaoxing Li
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China; Department of Pharmacology, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China
| | - Yu Zhang
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China; Department of Pharmacology, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China
| | - Yang Lv
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China; Department of Pharmacology, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China
| | - Mei-Ling Lu
- Department of Biochemistry, School of Life Science and Technology, China Pharmaceutical University, Nanjing 210009, China
| | - Min Luo
- Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore
| | - Meirong Chen
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China; Department of Pharmacology, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China.
| | - Yibei Xiao
- State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China; Department of Pharmacology, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China; Chongqing Innovation Institute of China Pharmaceutical University, Chongqing 401135, China.
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14
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Fichter KM, Setayesh T, Malik P. Strategies for precise gene edits in mammalian cells. MOLECULAR THERAPY. NUCLEIC ACIDS 2023; 32:536-552. [PMID: 37215153 PMCID: PMC10192336 DOI: 10.1016/j.omtn.2023.04.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
CRISPR-Cas technologies have the potential to revolutionize genetic medicine. However, work is still needed to make this technology clinically efficient for gene correction. A barrier to making precise genetic edits in the human genome is controlling how CRISPR-Cas-induced DNA breaks are repaired by the cell. Since error-prone non-homologous end-joining is often the preferred cellular repair pathway, CRISPR-Cas-induced breaks often result in gene disruption. Homology-directed repair (HDR) makes precise genetic changes and is the clinically desired pathway, but this repair pathway requires a homology donor template and cycling cells. Newer editing strategies, such as base and prime editing, can affect precise repair for relatively small edits without requiring HDR and circumvent cell cycle dependence. However, these technologies have limitations in the extent of genetic editing and require the delivery of bulky cargo. Here, we discuss the pros and cons of precise gene correction using CRISPR-Cas-induced HDR, as well as base and prime editing for repairing small mutations. Finally, we consider emerging new technologies, such as recombination and transposases, which can circumvent both cell cycle and cellular DNA repair dependence for editing the genome.
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Affiliation(s)
- Katye M. Fichter
- Division of Experimental Hematology and Cancer Biology, Cancer and Blood Disease Institute, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
| | - Tahereh Setayesh
- Division of Experimental Hematology and Cancer Biology, Cancer and Blood Disease Institute, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
| | - Punam Malik
- Division of Experimental Hematology and Cancer Biology, Cancer and Blood Disease Institute, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
- Division of Hematology, Cancer and Blood Disease Institute, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
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15
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Walker MG, Klompe S, Zhang D, Sternberg S. Novel molecular requirements for CRISPR RNA-guided transposition. Nucleic Acids Res 2023; 51:4519-4535. [PMID: 37078593 PMCID: PMC10201428 DOI: 10.1093/nar/gkad270] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Revised: 03/30/2023] [Accepted: 04/04/2023] [Indexed: 04/21/2023] Open
Abstract
CRISPR-associated transposases (CASTs) direct DNA integration downstream of target sites using the RNA-guided DNA binding activity of nuclease-deficient CRISPR-Cas systems. Transposition relies on several key protein-protein and protein-DNA interactions, but little is known about the explicit sequence requirements governing efficient transposon DNA integration activity. Here, we exploit pooled library screening and high-throughput sequencing to reveal novel sequence determinants during transposition by the Type I-F Vibrio cholerae CAST system (VchCAST). On the donor DNA, large transposon end libraries revealed binding site nucleotide preferences for the TnsB transposase, as well as an additional conserved region that encoded a consensus binding site for integration host factor (IHF). Remarkably, we found that VchCAST requires IHF for efficient transposition, thus revealing a novel cellular factor involved in CRISPR-associated transpososome assembly. On the target DNA, we uncovered preferred sequence motifs at the integration site that explained previously observed heterogeneity with single-base pair resolution. Finally, we exploited our library data to design modified transposon variants that enable in-frame protein tagging. Collectively, our results provide new clues about the assembly and architecture of the paired-end complex formed between TnsB and the transposon DNA, and inform the design of custom payload sequences for genome engineering applications with CAST systems.
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Affiliation(s)
- Matt W G Walker
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| | - Sanne E Klompe
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Dennis J Zhang
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| | - Samuel H Sternberg
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
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16
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Spínola-Amilibia M, Araújo-Bazán L, de la Gándara Á, Berger JM, Arias-Palomo E. IS21 family transposase cleaved donor complex traps two right-handed superhelical crossings. Nat Commun 2023; 14:2335. [PMID: 37087515 PMCID: PMC10122671 DOI: 10.1038/s41467-023-38071-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Accepted: 04/14/2023] [Indexed: 04/24/2023] Open
Abstract
Transposases are ubiquitous enzymes that catalyze DNA rearrangement events with broad impacts on gene expression, genome evolution, and the spread of drug-resistance in bacteria. Here, we use biochemical and structural approaches to define the molecular determinants by which IstA, a transposase present in the widespread IS21 family of mobile elements, catalyzes efficient DNA transposition. Solution studies show that IstA engages the transposon terminal sequences to form a high-molecular weight complex and promote DNA integration. A 3.4 Å resolution structure of the transposase bound to transposon ends corroborates our biochemical findings and reveals that IstA self-assembles into a highly intertwined tetramer that synapses two supercoiled terminal inverted repeats. The three-dimensional organization of the IstA•DNA cleaved donor complex reveals remarkable similarities with retroviral integrases and classic transposase systems, such as Tn7 and bacteriophage Mu, and provides insights into IS21 transposition.
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Affiliation(s)
- Mercedes Spínola-Amilibia
- Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, 28040, Spain
| | - Lidia Araújo-Bazán
- Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, 28040, Spain
| | - Álvaro de la Gándara
- Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, 28040, Spain
| | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Ernesto Arias-Palomo
- Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, 28040, Spain.
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17
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Walker MW, Klompe SE, Zhang DJ, Sternberg SH. Transposon mutagenesis libraries reveal novel molecular requirements during CRISPR RNA-guided DNA integration. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.19.524723. [PMID: 36711804 PMCID: PMC9882353 DOI: 10.1101/2023.01.19.524723] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
CRISPR-associated transposons (CASTs) direct DNA integration downstream of target sites using the RNA-guided DNA binding activity of nuclease-deficient CRISPR-Cas systems. Transposition relies on several key protein-protein and protein-DNA interactions, but little is known about the explicit sequence requirements governing efficient transposon DNA integration activity. Here, we exploit pooled library screening and high-throughput sequencing to reveal novel sequence determinants during transposition by the Type I-F Vibrio cholerae CAST system. On the donor DNA, large mutagenic libraries identified core binding sites recognized by the TnsB transposase, as well as an additional conserved region that encoded a consensus binding site for integration host factor (IHF). Remarkably, we found that VchCAST requires IHF for efficient transposition, thus revealing a novel cellular factor involved in CRISPR-associated transpososome assembly. On the target DNA, we uncovered preferred sequence motifs at the integration site that explained previously observed heterogeneity with single-base pair resolution. Finally, we exploited our library data to design modified transposon variants that enable in-frame protein tagging. Collectively, our results provide new clues about the assembly and architecture of the paired-end complex formed between TnsB and the transposon DNA, and inform the design of custom payload sequences for genome engineering applications of CAST systems.
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Affiliation(s)
- Matt W.G. Walker
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| | - Sanne E. Klompe
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, 10032, USA
| | - Dennis J. Zhang
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| | - Samuel H. Sternberg
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, 10032, USA
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18
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Precise cut-and-paste DNA insertion using engineered type V-K CRISPR-associated transposases. Nat Biotechnol 2023:10.1038/s41587-022-01574-x. [PMID: 36593413 DOI: 10.1038/s41587-022-01574-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 10/14/2022] [Indexed: 01/03/2023]
Abstract
CRISPR-associated transposases (CASTs) enable recombination-independent, multi-kilobase DNA insertions at RNA-programmed genomic locations. However, the utility of type V-K CASTs is hindered by high off-target integration and a transposition mechanism that results in a mixture of desired simple cargo insertions and undesired plasmid cointegrate products. Here we overcome both limitations by engineering new CASTs with improved integration product purity and genome-wide specificity. To do so, we engineered a nicking homing endonuclease fusion to TnsB (named HELIX) to restore the 5' nicking capability needed for cargo excision on the DNA donor. HELIX enables cut-and-paste DNA insertion with up to 99.4% simple insertion product purity, while retaining robust integration efficiencies on genomic targets. HELIX has substantially higher on-target specificity than canonical CASTs, and we identify several novel factors that further regulate targeted and genome-wide integration. Finally, we extend HELIX to other type V-K orthologs and demonstrate the feasibility of HELIX-mediated integration in human cell contexts.
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19
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First full views of a CRISPR-guided system for gene insertion. Nature 2023; 613:634-635. [PMID: 36631579 DOI: 10.1038/d41586-022-04584-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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20
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Park JU, Tsai AWL, Rizo AN, Truong VH, Wellner TX, Schargel RD, Kellogg EH. Structures of the holo CRISPR RNA-guided transposon integration complex. Nature 2023; 613:775-782. [PMID: 36442503 PMCID: PMC9876797 DOI: 10.1038/s41586-022-05573-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 11/17/2022] [Indexed: 11/30/2022]
Abstract
CRISPR-associated transposons (CAST) are programmable mobile genetic elements that insert large DNA cargos using an RNA-guided mechanism1-3. CAST elements contain multiple conserved proteins: a CRISPR effector (Cas12k or Cascade), a AAA+ regulator (TnsC), a transposase (TnsA-TnsB) and a target-site-associated factor (TniQ). These components are thought to cooperatively integrate DNA via formation of a multisubunit transposition integration complex (transpososome). Here we reconstituted the approximately 1 MDa type V-K CAST transpososome from Scytonema hofmannii (ShCAST) and determined its structure using single-particle cryo-electon microscopy. The architecture of this transpososome reveals modular association between the components. Cas12k forms a complex with ribosomal subunit S15 and TniQ, stabilizing formation of a full R-loop. TnsC has dedicated interaction interfaces with TniQ and TnsB. Of note, we observe TnsC-TnsB interactions at the C-terminal face of TnsC, which contribute to the stimulation of ATPase activity. Although the TnsC oligomeric assembly deviates slightly from the helical configuration found in isolation, the TnsC-bound target DNA conformation differs markedly in the transpososome. As a consequence, TnsC makes new protein-DNA interactions throughout the transpososome that are important for transposition activity. Finally, we identify two distinct transpososome populations that differ in their DNA contacts near TniQ. This suggests that associations with the CRISPR effector can be flexible. This ShCAST transpososome structure enhances our understanding of CAST transposition systems and suggests ways to improve CAST transposition for precision genome-editing applications.
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Affiliation(s)
- Jung-Un Park
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
| | - Amy Wei-Lun Tsai
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
| | - Alexandrea N Rizo
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
| | - Vinh H Truong
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
| | - Tristan X Wellner
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
| | - Richard D Schargel
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
| | - Elizabeth H Kellogg
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA.
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21
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Schmitz M, Querques I, Oberli S, Chanez C, Jinek M. Structural basis for the assembly of the type V CRISPR-associated transposon complex. Cell 2022; 185:4999-5010.e17. [PMID: 36435179 PMCID: PMC9798831 DOI: 10.1016/j.cell.2022.11.009] [Citation(s) in RCA: 33] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 09/26/2022] [Accepted: 11/09/2022] [Indexed: 11/27/2022]
Abstract
CRISPR-Cas systems have been co-opted by Tn7-like transposable elements to direct RNA-guided transposition. Type V-K CRISPR-associated transposons rely on the concerted activities of the pseudonuclease Cas12k, the AAA+ ATPase TnsC, the Zn-finger protein TniQ, and the transposase TnsB. Here we present a cryo-electron microscopic structure of a target DNA-bound Cas12k-transposon recruitment complex comprised of RNA-guided Cas12k, TniQ, a polymeric TnsC filament and, unexpectedly, the ribosomal protein S15. Complex assembly, mediated by a network of interactions involving the guide RNA, TniQ, and S15, results in R-loop completion. TniQ contacts two TnsC protomers at the Cas12k-proximal filament end, likely nucleating its polymerization. Transposition activity assays corroborate our structural findings, implying that S15 is a bona fide component of the type V crRNA-guided transposon machinery. Altogether, our work uncovers key mechanistic aspects underpinning RNA-mediated assembly of CRISPR-associated transposons to guide their development as programmable tools for site-specific insertion of large DNA payloads.
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Affiliation(s)
- Michael Schmitz
- Department of Biochemistry, University of Zurich, Zurich 8057, Switzerland
| | - Irma Querques
- Department of Biochemistry, University of Zurich, Zurich 8057, Switzerland
| | - Seraina Oberli
- Department of Biochemistry, University of Zurich, Zurich 8057, Switzerland
| | - Christelle Chanez
- Department of Biochemistry, University of Zurich, Zurich 8057, Switzerland
| | - Martin Jinek
- Department of Biochemistry, University of Zurich, Zurich 8057, Switzerland.
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