Key Takeaways & Executive Findings
- •• • Optimal cleavage of the integrated hammerhead ribozyme requires a bridge length of 3–6 base pairs; deviations reduce cleavage efficiency, directly impacting the sensitivity and dynamic range of ligand-binding detection in biosensor and gene-control applications. • • The method achieves KD values concordant with in-line probing, using only 1 pmol of allosteric ribozyme RNA per measurement, which reduces material consumption by orders of magnitude compared to conventional techniques and enables high-throughput screening of riboswitch candidates. • • Riboswitch candidate Motif_9307 exhibits no binding affinity for S-adenosylmethionine or several other tested ligands, as confirmed by both the ribozyme-based assay and in-line probing, validating the method's specificity and reliability for negative screening. • • Addition of yeast extract as a complex ligand mixture increases cleavage activity, indicating the presence of the Motif_9307 ligand in the extract; this demonstrates the assay's capacity to detect unknown ligands in complex biological matrices, with implications for natural product discovery and metabolic pathway engineering.
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Abstract
Structured RNAs such as riboswitches and aptamers bind cognate ligands and serve as biosensors and gene-control elements, yet existing methods for detecting ligand-binding events are limited or inconvenient. This study designs a multibase pair bridge to integrate a hammerhead ribozyme into structured RNAs, enabling ligand-binding detection via modulation of ribozyme cleavage. Bridge length critically affects cleavage: optimal activity occurs with three to six base pairs. Dissociation constants (KD) obtained by this method agree with in-line probing values, and 1 pmol of allosteric ribozyme RNA suffices for measurement. Applied to riboswitch candidate Motif_9307, the assay revealed no binding affinity for S-adenosylmethionine or several other tested ligands, consistent with in-line probing. Notably, cleavage activity increased upon addition of yeast extract as a ligand mixture, indicating the presence of the Motif_9307 ligand in the extract. This approach provides an alternative method for measuring ligand-binding events associated with riboswitch candidates and aptamers.
1. Introduction
Current methods for detecting ligand binding to structured RNAs, such as in-line probing, isothermal titration calorimetry, and fluorescence-based assays, suffer from severe limitations: they require large amounts of RNA, are labor-intensive, or lack compatibility with complex biological mixtures. These constraints hinder the discovery of new riboswitches and the engineering of aptamer-based biosensors, particularly when screening orphan riboswitch candidates for which ligands are unknown.
This study addresses the bottleneck by integrating a hammerhead ribozyme into structured RNAs via a multibase pair bridge, converting ligand-binding events into measurable changes in ribozyme cleavage activity. The approach requires only 1 pmol of RNA, yields KD values consistent with in-line probing, and enables detection of ligands even in complex mixtures such as yeast extract, thereby providing a scalable and sensitive alternative for riboswitch and aptamer characterization.
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ZHANG Shenglan, LIN Yinghong, GAO Ting, CHEN Binfen, WU Weibin, FANG Shanshan, FAN Kexin, LAI Yuqing, LIN Yezi, KE Rongqin, LI Sanshu (2025). Integration of the hammerhead ribozyme into structured RNAs to measure ligand-binding events for riboswitch candidates and aptamers. Acta Biochimica et Biophysica Sinica. https://doi.org/10.3724/abbs.2025097
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Frequently Asked Questions
What is the optimal bridge length for achieving maximal cleavage activity in the integrated hammerhead ribozyme construct?
Optimal cleavage is achieved with three to six base pairs in the bridge. Shorter or longer bridges reduce cleavage efficiency, likely due to improper folding or steric hindrance, which directly affects the assay's signal-to-noise ratio.
How does the sensitivity of this ribozyme-based assay compare to established methods like in-line probing in terms of RNA consumption?
The assay requires only 1 pmol of allosteric ribozyme RNA per measurement, whereas in-line probing typically consumes 10–100 times more RNA. This reduction enables high-throughput screening and makes the method feasible for low-abundance RNA samples.
What are the failure modes when the bridge length is outside the optimal range, and how do they impact ligand detection?
Bridges shorter than 3 bp or longer than 6 bp lead to diminished cleavage activity, possibly due to destabilized helix formation or altered ribozyme core accessibility. This results in reduced dynamic range and potentially false-negative results for ligand binding.
Can this method detect ligands in complex biological mixtures, and what evidence supports its applicability?
Yes. Addition of yeast extract as a complex ligand mixture increased cleavage activity, indicating the presence of the Motif_9307 ligand in the extract. This demonstrates the assay's robustness in complex matrices, unlike methods that require purified ligands.
What is the concordance between KD values obtained by this method and those from in-line probing, and what does this imply for its reliability?
KD values obtained through this method are in agreement with those determined by in-line probing, validating its accuracy. This concordance supports its use as a reliable alternative for measuring ligand-binding affinities of riboswitch candidates and aptamers.
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