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Updated: Mar 16, 2026
Gene Digital Circuits Based on CRISPR-Cas Systems and Anti-CRISPR Proteins
Published on: October 18, 2022
AcrIIA7 hijacks tracrRNA to block CRISPR-Cas system
So Yeon Lee1,2, Hyun Ho Park3,4
1College of Pharmacy, Chung-Ang University, Seoul, Republic of Korea.
Abstract:
The CRISPR-Cas9 system provides adaptive immunity against invading genetic elements through a dual-RNA-guided DNA cleavage mechanism. This system relies on the precise assembly of a ribonucleoprotein (RNP) complex composed of the Cas9 endonuclease, a CRISPR-derived RNA (crRNA), and a trans-activating CRISPR RNA (tracrRNA). Around 100 anti-CRISPR proteins that inhibit CRISPR-Cas systems have been identified, and the mechanisms by which they act are increasingly being elucidated. However, the inhibitory mechanisms of many Acrs, including AcrIIA7, remain poorly understood. Here, we present the structure of AcrIIA7 and uncover a previously unrecognized mechanism by which it inhibits Cas9 function. Structural and biochemical analyses reveal that AcrIIA7 specifically binds to tracrRNA, preventing its association with crRNA and thereby blocking formation of the active Cas9 RNP complex. This tracrRNA hijacking mechanism represents a unique strategy for CRISPR inhibition, in which an anti-CRISPR protein targets an RNA scaffold essential for Cas9 activation rather than interacting directly with the Cas9 protein. Our findings provide the first structural insight into tracrRNA-targeted anti-CRISPR activity and highlight RNA-RNA interaction interfaces as vulnerable nodes in CRISPR-Cas immunity.
Insights
A novel anti-CRISPR protein, AcrIIA7, inhibits CRISPR-Cas9 by binding to tracrRNA, preventing the formation of the essential ribonucleoprotein complex. This discovery reveals a new RNA-targeting mechanism for blocking CRISPR immunity.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The CRISPR-Cas9 system is a powerful gene-editing tool relying on a ribonucleoprotein (RNP) complex.
- Anti-CRISPR proteins (Acrs) are known inhibitors of CRISPR-Cas systems, but their mechanisms are not fully understood.
- AcrIIA7's inhibitory mechanism against Cas9 was previously unclear.
Purpose of the Study:
- To elucidate the inhibitory mechanism of the anti-CRISPR protein AcrIIA7 against the CRISPR-Cas9 system.
- To determine the structural basis for AcrIIA7's interaction with Cas9 components.
- To identify novel strategies for CRISPR-Cas system inhibition.
Main Methods:
- X-ray crystallography to determine the structure of AcrIIA7.
- Biochemical assays to analyze the interaction between AcrIIA7, Cas9, crRNA, and tracrRNA.
- Structural analysis to understand the binding interface and mechanism of inhibition.
Main Results:
- The structure of AcrIIA7 was determined, revealing its unique inhibitory mechanism.
- AcrIIA7 specifically binds to the trans-activating CRISPR RNA (tracrRNA).
- This binding prevents the association of tracrRNA with CRISPR-derived RNA (crRNA), inhibiting the formation of the active Cas9 RNP complex.
Conclusions:
- AcrIIA7 employs a novel 'tracrRNA hijacking' mechanism to inhibit CRISPR-Cas9.
- This study provides the first structural insights into tracrRNA-targeted anti-CRISPR activity.
- RNA-RNA interaction interfaces are identified as critical targets for modulating CRISPR-Cas immunity.
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