Modified Cas12a2 Variants for Tuned RNA Detection and DNA Sparing
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Solution Overview
Problem
The molecular basis of duplex DNA degradation by Cas12a2 remains enigmatic, and existing CRISPR-Cas systems face challenges with collateral DNA degradation and resistance to anti-CRISPR proteins.
Innovation Solution
Development of variant Cas12a2 molecules with distinct structural and functional properties, including recognition of single-stranded RNA and unique insertion domains, enabling targeted nucleic acid cleavage and resistance to anti-CRISPR proteins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Cas12a systems are used to target and degrade mobile genetic elements, then bacterial immunity is achieved, but collateral degradation of dsDNA occurs
Solution Approach 1:
The patent extracts the RuvC nuclease domain from Cas12a2 to create a catalytically inactive variant. This removed domain is responsible for the harmful collateral degradation of dsDNA, while the remaining structure retains the ability to recognize target RNA and provide immune function through abortive infection mechanism.
Solution Approach 2:
The patent converts the potentially harmful collateral DNA degradation activity into a beneficial diagnostic tool. By controlling and monitoring the collateral activity, it can be used to detect target RNA presence through collateral cleavage of reporter molecules, transforming a harmful side effect into a useful detection mechanism.
2Reliability
If Cas12a systems are used for target recognition, then mobile genetic elements are degraded, but resistance to anti-CRISPR proteins is reduced
Solution Approach 1:
The patent inverts the mechanism from active degradation to abortive infection. Instead of degrading target DNA, Cas12a2 recognizes target RNA and triggers bacterial suicide, providing immunity without requiring nuclease activity against the target, thereby evading anti-CRISPR proteins that target nuclease domains.
Solution Approach 2:
The patent changes the fundamental parameter of the immune mechanism from nuclease-mediated degradation to abortive infection. This parameter change alters the interaction landscape, making the system insensitive to anti-CRISPR proteins that specifically inhibit nuclease activity.
3Measurement precision
If Cas12a2 recognizes RNA target strand with PFS, then specific cleavage is achieved, but molecular basis of duplex degradation remains enigmatic
Solution Approach 1:
The patent segments the analysis by separately characterizing RNA target recognition (with high specificity through PFS) and dsDNA degradation (collateral activity). This segmentation allows independent optimization and understanding of each function, clarifying that they operate through distinct molecular mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Cas12a2 variants achieve specific and efficient nucleic acid cleavage, overcoming collateral DNA degradation and anti-CRISPR resistance, providing enhanced bacterial immunity against mobile genetic elements.
Implementation Method 1
Prokaryotic adaptive immunity typically utilizes CRISPR-Cas systems to target and degrade mobile genetic elements
Implementation Method 2
The cell killing activity of Cas12a2 is mediated by robust, nonspecific cleavage of single-stranded (ss)RNA, ssDNA, and dsDNA unleashed by recognition of a target RNA
Implementation Method 3
the collateral degradation of dsDNA stands is unique to Cas12a2, suggesting a distinct mechanism of activation
Implementation Method 4
Cas12a2 from Sulfuricurvum sp. PC08-66 instead relies on abortive infection—that is, bacterial suicide in response to the presence of an invader—to achieve population-level immunity
Implementation Method 5
Cas12a2 recognizes an RNA target strand with a suitable protospacer-flanking sequence (PFS) rather than the double-stranded (ds)DNA target of Cas12a
Implementation Method 6
Cas12a2 lacks a Nuc domain (involved in DNA target strand loading), but instead contains a zinc-ribbon and a unique insertion domain
Implementation Method 7
Cas12a2 is immune to the effects of many anti-CRISPR (Acr) proteins that target Cas12a
Data Source
AI summary
RNA-targeting Cas12a2 complex allows for rationale design of Cas12a2 into a versatile enzyme capable of non-specifically degrading distinct types of nucleic acid targets depending on mutations of the active site residues and residues that stabilize bound targets. These mutations allow for tuning of output signal associated with RNA detection. By mutating specific residues, indiscriminate single-stranded RNase and DNase and double-stranded DNase activity can be modified to only cleave single-stranded DNA and single-stranded RNA, or only single-stranded DNA. This allows for diagnostic tools which can provide a detection. Residues involved in binding the non-self vs. self-recognition signal (PFS) can also be modified so larger subsets of nucleic acid targets can be recognized.