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Liang Y, Willey S, Chung YC, Lo YM, Miao S, Rundell S, Tu LC, Bong D. Intracellular RNA and DNA tracking by uridine-rich internal loop tagging with fluorogenic bPNA. Nat Commun 2023; 14:2987. [PMID: 37225690 DOI: 10.1038/s41467-023-38579-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Accepted: 05/05/2023] [Indexed: 05/26/2023] Open
Abstract
The most widely used method for intracellular RNA fluorescence labeling is MS2 labeling, which generally relies on the use of multiple protein labels targeted to multiple RNA (MS2) hairpin structures installed on the RNA of interest (ROI). While effective and conveniently applied in cell biology labs, the protein labels add significant mass to the bound RNA, which potentially impacts steric accessibility and native RNA biology. We have previously demonstrated that internal, genetically encoded, uridine-rich internal loops (URILs) comprised of four contiguous UU pairs (8 nt) in RNA may be targeted with minimal structural perturbation by triplex hybridization with 1 kD bifacial peptide nucleic acids (bPNAs). A URIL-targeting strategy for RNA and DNA tracking would avoid the use of cumbersome protein fusion labels and minimize structural alterations to the RNA of interest. Here we show that URIL-targeting fluorogenic bPNA probes in cell media can penetrate cell membranes and effectively label RNAs and RNPs in fixed and live cells. This method, which we call fluorogenic U-rich internal loop (FLURIL) tagging, was internally validated through the use of RNAs bearing both URIL and MS2 labeling sites. Notably, a direct comparison of CRISPR-dCas labeled genomic loci in live U2OS cells revealed that FLURIL-tagged gRNA yielded loci with signal to background up to 7X greater than loci targeted by guide RNA modified with an array of eight MS2 hairpins. Together, these data show that FLURIL tagging provides a versatile scope of intracellular RNA and DNA tracking while maintaining a light molecular footprint and compatibility with existing methods.
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Affiliation(s)
- Yufeng Liang
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH, USA
- Center for RNA Biology, The Ohio State University, Columbus, OH, USA
| | - Sydney Willey
- Center for RNA Biology, The Ohio State University, Columbus, OH, USA
- Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, OH, USA
- The Ohio State University Comprehensive Cancer Center, The Ohio State University, Columbus, OH, USA
| | - Yu-Chieh Chung
- Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, OH, USA
| | - Yi-Meng Lo
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH, USA
- Center for RNA Biology, The Ohio State University, Columbus, OH, USA
| | - Shiqin Miao
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH, USA
- Center for RNA Biology, The Ohio State University, Columbus, OH, USA
| | - Sarah Rundell
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH, USA
- Center for RNA Biology, The Ohio State University, Columbus, OH, USA
| | - Li-Chun Tu
- Center for RNA Biology, The Ohio State University, Columbus, OH, USA.
- Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, OH, USA.
- The Ohio State University Comprehensive Cancer Center, The Ohio State University, Columbus, OH, USA.
| | - Dennis Bong
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH, USA.
- Center for RNA Biology, The Ohio State University, Columbus, OH, USA.
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Munyaradzi O, Rundell S, Bong D. Impact of bPNA Backbone Structural Constraints and Composition on Triplex Hybridization with DNA. Chembiochem 2022; 23:e202100707. [PMID: 35167719 PMCID: PMC9136932 DOI: 10.1002/cbic.202100707] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2021] [Revised: 01/18/2022] [Indexed: 11/07/2022]
Abstract
We report herein a study on the impact of bifacial peptide nucleic acid (bPNA) amino acid composition and backbone modification on DNA binding. A series of bPNA backbone variants with identical net charge were synthesized to display either 4 or 6 melamine (M) bases. These bases form thymine-melamine-thymine (TMT) base-triples, resulting in triplex hybrid stem structures with T-rich DNAs. Analyses of 6 M bPNA-DNA hybrids suggested that hybrid stability was linked to amino acid secondary structure propensities, prompting a more detailed study in shorter 4 M bPNAs. We synthesized 4 M bPNAs predisposed to adopt helical secondary structure via helix-turn nucleation in 7-residue bPNAs using double-click covalent stapling. Generally, hybrid stability improved upon stapling, but amino acid composition had a more significant effect. We also pursued an alternative strategy for bPNA structural preorganization by incorporation of residues with strong backbone amide conformational preferences such as 4R- and 4S-fluoroprolines. Notably, these derivatives exhibited an additional improvement in hybrid stability beyond both unsubstituted proline bPNA analogues and the helically patterned bPNAs. Overall, these findings demonstrate the tunability of bPNA-DNA hybrid stability through bPNA backbone structural propensities and amino acid composition.
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Affiliation(s)
- Oliver Munyaradzi
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio, 43210, USA
| | - Sarah Rundell
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio, 43210, USA
| | - Dennis Bong
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio, 43210, USA
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Devari S, Bhunia D, Bong D. Synthesis of bifacial Peptide Nucleic Acids with diketopiperazine backbones. Synlett 2022; 33:965-968. [DOI: 10.1055/a-1802-6873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
We report herein synthesis of bifacial peptide nucleic acids (bPNAs) with novel diketopiperazine (DKP) backbones that display unnatural melamine (M) bases as well as native bases. To examine the structure-function scope of diketopiperazine bPNAs, we synthesized a set of bPNAs using diaminopropionic acid, diaminobutyric acid, ornithine and lysine derivatives to display the base-tripling motifs, which result in 1, 2, 3, and 4 carbons linking alpha carbon to sidechain amine, respectively. Thermal denaturation of DNA hybrids with these bPNAs revealed that the optimal sidechain linkage was 4 carbons, corresponding to the lysine derivative. Accordingly, monomers displaying two bases per sidechain were prepared via double reductive alkylation of the ε-amine of Fmoc-Lysine with acetaldehyde derivatives of adenine, cytidine, uridine and melamine. With these building blocks in hand, diketopiperazine bPNAs were prepared to display a combination of native and synthetic (melamine) bases. Preliminary melting studies indicate binding signatures of cytidine and melamine-displaying bPNAs to T-rich DNAs, though full characterization of this behavior is ongoing. We anticipate that the straightforward synthetic methodology developed herein will enable further studies on noncanonical nucleic acid hybridization with diketopiperazine backbones.
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Affiliation(s)
- Shekaraiah Devari
- Chemistry & Biochemistry, The Ohio State University, Columbus, United States
| | - Debmalya Bhunia
- Chemistry & Biochemistry, The Ohio State University, Columbus, United States
| | - Dennis Bong
- Chemistry & Biochemistry, The Ohio State University, Columbus, United States
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Liang Y, Miao S, Mao J, Devari S, Gonzalez M, Bong D. Screening of Minimalist Noncanonical Sites in Duplex DNA and RNA Reveals Context and Motif-Selective Binding by Fluorogenic Base Probes. Chemistry 2022; 28:e202103616. [PMID: 34693570 PMCID: PMC8758549 DOI: 10.1002/chem.202103616] [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: 10/06/2021] [Indexed: 01/12/2023]
Abstract
We hypothesize that programmable hybridization to noncanonical nucleic acid motifs may be achieved by macromolecular display of binders to individual noncanonical pairs (NCPs). As each recognition element may individually have weak binding to an NCP, we developed a semi-rational approach to detect low affinity interactions between selected nitrogenous bases and noncanonical sites in duplex DNA and RNA. A set of fluorogenic probes was synthesized by coupling abiotic (triazines, pyrimidines) and native RNA bases to thiazole orange (TO) dye. This probe library was screened against duplex nucleic acid substrates bearing single abasic, single NCP, and tandem NCP sites. Probe engagement with NCP sites was reported by 100-1000× fluorescence enhancement over background. Binding is strongly context-dependent, reflective of both molecular recognition and stability: less stable motifs are more likely to bind a synthetic probe. Further, DNA and RNA substrates exhibit entirely different abasic and single NCP binding profiles. While probe binding in the abasic and single NCP screens was monotonous, much richer binding profiles were observed with the screen of tandem NCP sites in RNA, in part due to increased steric accessibility. In addition to known binding interactions between the triazine melamine (M) and T/U sites, the NCP screens identified new targeting elements for pyrimidine-rich motifs in single NCPs and 2×2 internal bulges. We anticipate that semi-rational approaches of this type will lead to programmable noncanonical hybridization strategies at the macromolecular level.
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Affiliation(s)
- Yufeng Liang
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210
| | - Shiqin Miao
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210
| | - Jie Mao
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210
| | - Shekaraiah Devari
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210
| | - Maricarmen Gonzalez
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210
| | - Dennis Bong
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210
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Rundell S, Munyaradzi O, Bong D. Enhanced Triplex Hybridization of DNA and RNA via Syndiotactic Side Chain Presentation in Minimal bPNAs. Biochemistry 2021; 61:85-91. [PMID: 34955016 DOI: 10.1021/acs.biochem.1c00693] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
General design principles for recognition at noncanonical interfaces of DNA and RNA remain elusive. Triplex hybridization of bifacial peptide nucleic acids (bPNAs) with oligo-T/U DNAs and RNAs is a robust recognition platform that can be used to define structure-function relationships in synthetic triplex formation. To this end, a set of minimal (mw < 1 kD) bPNA variants was synthesized to probe the impact of amino acid secondary structural propensity, stereochemistry, and backbone cyclization on hybridization with short, unstructured T-rich DNA and U-rich RNAs. Thermodynamic parameters extracted from optical melting analyses of bPNA variant hybrids indicated that there are two bPNA backbone modifications that significantly improve hybridization: alternating (d, l) configuration in open-chain dipeptides and homochiral dipeptide cyclization to diketopiperazine. Further, binding to DNA is preferred over RNA for all bPNA variants. Thymine-uracil substitutions in DNA substrates revealed that the methyl group of thymine accounts for 71% of ΔΔGDNA-RNA for open-chain bPNAs but only 40% of ΔΔGDNA-RNA for diketopiperazine bPNA, suggesting a greater sensitivity to RNA conformation and more optimized stacking in the cyclic bPNA. Together, these data reveal pressure points for tuning triplex hybridization at the chiral centers of bPNA, backbone conformation, stacking effects at the base triple, and the nucleic acid substrate itself. A structural blueprint for enhancing bPNA targeting of both DNA and RNA substrates includes syndiotactic base presentation (as found in homochiral diketopiperazines and d, l peptides), expansion of base stacking, and further investigation of bPNA backbone preorganization.
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Affiliation(s)
- Sarah Rundell
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210, United States
| | - Oliver Munyaradzi
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210, United States
| | - Dennis Bong
- Department of Chemistry & Biochemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210, United States
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Miao S, Bhunia D, Devari S, Liang Y, Munyaradzi O, Rundell S, Bong D. Bifacial PNAs Destabilize MALAT1 by 3' A-Tail Displacement from the U-Rich Internal Loop. ACS Chem Biol 2021; 16:1600-1609. [PMID: 34382766 DOI: 10.1021/acschembio.1c00575] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We report herein a new class of synthetic reagents for targeting the element for nuclear expression (ENE) in MALAT1, a long noncoding RNA upregulated in many cancers. The cis-acting ENE contains a U-rich internal loop (URIL) that forms an 11 base UAU-rich triplex stem with the truncated 3' oligo-A tail of MALAT1, protecting the terminus from exonuclease digestion and greatly extending transcript lifetime. Bifacial peptide nucleic acids (bPNAs) similarly bind URILs via base triple formation between two uracil bases and a synthetic base, melamine. We synthesized a set of low molecular weight bPNAs composed of α-linked peptide, isodipeptide, and diketopiperazine backbones and evaluated their ENE binding efficacy in vitro via oligo-A strand displacement and consequent exonuclease sensitivity. Degradation was greatly enhanced by bPNA treatment in the presence of exonucleases, with ENE half-life plunging to 6 min from >24 h. RNA digestion kinetics could clearly distinguish between bPNAs with similar URIL affinities, highlighting the utility of functional assays for evaluating synthetic RNA binders. In vitro activity was mirrored by a 50% knockdown of MALAT1 expression in pancreatic cancer (PANC-1) cells upon treatment with bPNAs, consistent with intracellular digestion triggered by a similar ENE A-tail displacement mechanism. Pulldown from PANC-1 total RNA with biotinylated bPNA enriched MALAT1 > 4000× , supportive of bPNA-URIL selectivity. Together, these experiments establish the feasibility of native transcript targeting by bPNA in both in vitro and intracellular contexts. Reagents such as bPNAs may be useful tools for the investigation of transcripts stabilized by cis-acting poly(A) binding RNA elements.
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Affiliation(s)
- Shiqin Miao
- Department of Chemistry & Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Debmalya Bhunia
- Department of Chemistry & Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Shekaraiah Devari
- Department of Chemistry & Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Yufeng Liang
- Department of Chemistry & Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Oliver Munyaradzi
- Department of Chemistry & Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Sarah Rundell
- Department of Chemistry & Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Dennis Bong
- Department of Chemistry & Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
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Miao S, Liang Y, Rundell S, Bhunia D, Devari S, Munyaradzi O, Bong D. Unnatural bases for recognition of noncoding nucleic acid interfaces. Biopolymers 2021; 112:e23399. [PMID: 32969496 PMCID: PMC7855516 DOI: 10.1002/bip.23399] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 08/14/2020] [Accepted: 08/25/2020] [Indexed: 12/20/2022]
Abstract
The notion of using synthetic heterocycles instead of the native bases to interface with DNA and RNA has been explored for nearly 60 years. Unnatural bases compatible with the DNA/RNA coding interface have the potential to expand the genetic code and co-opt the machinery of biology to access new macromolecular function; accordingly, this body of research is core to synthetic biology. While much of the literature on artificial bases focuses on code expansion, there is a significant and growing effort on docking synthetic heterocycles to noncoding nucleic acid interfaces; this approach seeks to illuminate major processes of nucleic acids, including regulation of transcription, translation, transport, and transcript lifetimes. These major avenues of research at the coding and noncoding interfaces have in common fundamental principles in molecular recognition. Herein, we provide an overview of foundational literature in biophysics of base recognition and unnatural bases in coding to provide context for the developing area of targeting noncoding nucleic acid interfaces with synthetic bases, with a focus on systems developed through iterative design and biophysical study.
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Affiliation(s)
- Shiqin Miao
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA
| | - Yufeng Liang
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA
| | - Sarah Rundell
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA
| | - Debmalya Bhunia
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA
| | - Shekar Devari
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA
| | - Oliver Munyaradzi
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA
| | - Dennis Bong
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, USA
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