Anti-CRISPR with non-protein substances

Heparin Specifically Inhibits CRISPR/Cas12 Activation, Enabling Ultrasensitive Heparin Detection and Gene Editing Regulation

Heparin is a highly sulfated linear glycosaminoglycan that is used as an anticoagulant to prevent and treat thrombotic diseases. Herein, we find that heparin specifically inhibits the activation of the Cas12 protein through the competitive binding of heparin and crRNA to Cas12. Studies illustrate that heparin's high molecular weight and strong negative charge are critical parameters for its inhibitory effect. This unexpected finding was engineered for the detection of heparin, affording a low detection limit of 0.36 ng/mL for fluorometric quantification. We further developed a rapid lateral flow-based system named HepaStrip (heparin strip), allowing heparin monitoring in clinical samples within 20 min. Finally, in vivo investigations revealed that heparin can regulate gene editing with the clusters of the regularly spaced short palindromic repeat (CRISPR)/Cas12 system in Escherichia coli. Heparin blocks the formation of Cas12-crRNA ribonucleoprotein, allowing the application of CRISPR for rapid and field-deployable detection of heparin and unleashing the potential use of heparin in future anti-CRISPR applications.

Postamplifying Cas12a Activation through Hybridization Chain Reaction-Triggered Fluorescent Nanocluster Formation for Ultrasensitive Nucleic Acid Detection

CRISPR/Cas12a-based biosensing is advancing rapidly; however, achieving sensitive and cost-effective reporting of Cas12a activation remains a challenge. In response, we have developed a label-free system capable of postamplifying Cas12a activation by integrating hybridization chain reaction (HCR) and DNA-copper nanoclusters (DNA-CuNCs). The trans-cleavage of Cas12a triggers a silenced HCR, leading to the in situ assembly of fluorescent DNA-CuNCs, allowing for the turn-on reporting of Cas12a activation. Without preamplification, this assay can detect DNA with a detection limit of 5 fM. Furthermore, when coupled with preamplification, the system achieves exceptional sensitivity, detecting the monkeypox virus (MPXV) plasmid at 1 copy in human serum. In a MPXV pseudovirus-based validation test, the obtained results are in agreement with those obtained by qPCR, reinforcing the robustness of this method. Our study represents the first effort to manipulate DNA-CuNC formation on HCR for highly sensitive and cost-effective reporting of Cas12a, resulting in an efficient synthetic biology-enabled sensing platform for biosafety applications.