LUCas: Light-Uncaged Cas13a using photocleavable interfering guide RNAs.

Area of Science:

• Molecular Biology
• Biotechnology
• Diagnostic Assays

Background:

• CRISPR diagnostics, particularly using Cas13a, offer sensitive, amplification-free RNA detection via collateral cleavage.
• Limitations include background enzyme activity and reaction initiation variability, hindering assay sensitivity and interpretation.
• A controllable 'start' mechanism for Cas13a is needed to overcome these challenges.

Purpose of the Study:

• To develop a light-controlled system for precise Cas13a activation, addressing limitations in CRISPR diagnostics.
• To enhance assay sensitivity, interpretability, and expand design possibilities for Cas13a-based detection.
• To demonstrate novel multiplexed detection strategies using light-gated Cas13a.

Main Methods:

• Introduction of Light-Uncaged Cas13a (LUCas), utilizing a photocleavable interfering guide RNA (pc-igRNA) to gate Cas13a activity.
• UV illumination to release pc-igRNA suppression, restoring Cas13a's trans-cleavage activity.
• Quantitative kinetic analysis, limit-of-detection prediction and validation, and demonstration of temporal barcoding for multiplexed detection.

Main Results:

• LUCas demonstrates approximately 100-fold suppression of Cas13a trans-cleavage activity prior to photo-activation.
• The system effectively suppresses target-independent background activity, allowing predictive sensitivity determination.
• Experimental validation confirmed the predicted limit-of-detection, and temporal barcoding enabled multiplexed viral co-infection detection.

Conclusions:

• LUCas provides a robust framework for light-based, mechanistically informed control of Cas13a activity in diagnostic applications.
• This system significantly improves sensitivity and interpretability in CRISPR-based diagnostics.
• LUCas enables advanced multiplexed detection strategies, expanding the utility of CRISPR diagnostics for complex biological samples.