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In molecular programming, the Chemical Reaction Network model is often used to describe real or hypothetical systems. Often, an interesting computational task can be done with a known hypothetical Chemical Reaction Network, but often such networks have no known physical implementation. One of the important breakthroughs in the field was that any Chemical Reaction Network can be physically implemented, approximately, using DNA strand displacement mechanisms. This allows us to treat the Chemical Reaction Network model as a programming language and the implementation schemes as its compiler. This also suggests that it would be useful to optimize the result of such a compilation, and in general to find effective ways to design better DNA strand displacement systems. We discuss DNA strand displacement systems in terms of "motifs", short sequences of elementary DNA strand displacement reactions. We argue that describing such motifs in terms of their inputs and outputs, then building larger systems out of the abstracted motifs, can be an efficient way of designing DNA strand displacement systems. We discuss four previously studied motifs in this abstracted way, and present a new motif based on cooperative 4-way strand exchange. We then show how Chemical Reaction Network implementations can be built out of abstracted motifs, discussing existing implementations as well as presenting two new implementations based on 4-way strand exchange, one of which uses the new cooperative motif. The new implementations both have two desirable properties not found in existing implementations, namely both use only at most 2-stranded DNA complexes for signal and fuel complexes and both are physically reversible. There are reasons to believe that those properties may make them more robust and energy-efficient, but at the expense of using more fuel complexes than existing implementation schemes.
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Customizable Aptamer Transducer Network Designed for Feed-Forward Coupling
Solution-based biosensors that utilize aptamers have been engineered in a variety of formats to detect a range of analytes for both medical and environmental applications. However, since aptamers have fixed base sequences, incorporation of aptamers into DNA strand displacement networks for feed-forward signal amplification and processing requires significant redesign of downstream DNA reaction networks. We designed a novel aptamer transduction network that releases customizable output domains, which can then be used to initiate downstream strand displacement reaction networks without any sequence redesign of the downstream reaction networks. In our aptamer transducer (AT), aptamer input domains are independent of output domains within the same DNA complex and are reacted with a fuel strand after aptamer–ligand binding. ATs were designed to react with two fluorescent dye-labeled reporter complexes to show the customizability of the output domains, as well as being used as feed-forward inputs to two previously studied catalytic reaction networks, which can be used as amplifiers. Through our study, we show both successful customizability and feed-forward capability of our ATs.
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- Award ID(s):
- 1706065
- PAR ID:
- 10299220
- Date Published:
- Journal Name:
- ACS Omega
- ISSN:
- 2470-1343
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Aptamers are widely employed as recognition elements in small molecule biosensors due to their ability to recognize small molecule targets with high affinity and selectivity. Structure-switching aptamers are particularly promising for biosensing applications because target-induced conformational change can be directly linked to a functional output. However, traditional evolution methods do not select for the significant conformational change needed to create structure-switching biosensors. Modified selection methods have been described to select for structure-switching architectures, but these remain limited by the need for immobilization. Herein we describe the first homogenous, structure-switching aptamer selection that directly reports on biosensor capacity for the target. We exploit the activity of restriction enzymes to isolate aptamer candidates that undergo target-induced displacement of a short complementary strand. As an initial demonstration of the utility of this approach, we performed selection against kanamycin A. Four enriched candidate sequences were successfully characterized as structure-switching biosensors for detection of kanamycin A. Optimization of biosensor conditions afforded facile detection of kanamycin A (90 μM to 10 mM) with high selectivity over three other aminoglycosides. This research demonstrates a general method to directly select for structure-switching biosensors and can be applied to a broad range of small-molecule targets.more » « less
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Abstract In vitro aptamer isolation methods can yield hundreds of potential candidates, but selecting the optimal aptamer for a given application is challenging and laborious. Existing aptamer characterization methods either entail low-throughput analysis with sophisticated instrumentation, or offer the potential for higher throughput at the cost of providing a relatively increased risk of false-positive or -negative results. Here, we describe a novel method for accurately and sensitively evaluating the binding between DNA aptamers and small-molecule ligands in a high-throughput format without any aptamer engineering or labeling requirements. This approach is based on our new finding that ligand binding inhibits aptamer digestion by T5 exonuclease, where the extent of this inhibition correlates closely with the strength of aptamer-ligand binding. Our assay enables accurate and efficient screening of the ligand-binding profiles of individual aptamers, as well as the identification of the best target binders from a batch of aptamer candidates, independent of the ligands in question or the aptamer sequence and structure. We demonstrate the general applicability of this assay with a total of 106 aptamer-ligand pairs and validate these results with a gold-standard method. We expect that our assay can be readily expanded to characterize small-molecule-binding aptamers in an automated, high-throughput fashion.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/acsomega.1c03146
