In the evolutionary arms race between phage and bacteria, mutations can allow phages to escape CRISPR-Cas-mediated destruction. However, bacteria are quick to acquire new spacer sequences which allow them to retarget phage mutants. Anti-CRISPR proteins are another defense mechanism for phages to escape destruction from CRISPR-Cas systems.
There are 22 unique families of anti-CRISPR proteins. Some act by disrupting DNA binding and others inhibit the cleavage of target sequences.The first anti-CRISPR proteins were identified in 2013 by a research group lead by Alan R. Davidson at University of Toronto . Anti-CRISPR proteins have been identified in multiple bacteria genera that target type I and type II CRISPR-Cas systems.Anti-CRISPR proteins that target the CRISPR-Cas9 system, commonly used for genome editing were identified in 2016 and 2017 by Davidson’s group and Joseph Bondy-Denomy’s group at University of California, San Francisco. In genome editing for therapeutic uses, anti-CRISPR proteins may provide a valuable “off switch” for better control of Cas9 activity. Anti-CRISPR proteins have been shown to reduce off-target cutting by CRISPR-Cas9 in human cells.
Defense Advanced Research Projects Agency (DARPA) supported two research studies published in Science in 2018 that identified new anti-CRISPR proteins, including one that inhibits CRISPR-Cas12a, which is becoming more popular for genome editing applications. DARPA supported this research because of the potential for anti-CRISPR proteins to be used as a countermeasure against nefarious use of CRISPR.The two research groups are Jennifer Doudna’s at University of California, Berkeley and Bondy-Denomy’s group.Jennifer Doudna previously founded the company Caribou Biosciences which is developing various applications for CRISPR-Cas technology.
Systematic discovery of natural CRISPR-Cas12a inhibitors
Kyle E. Watters, Christof Fellmann, Hua B. Bai, Shawn M. Ren, Jennifer A. Doudna
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Adding this protein to human cells makes CRISPR-Cas9 more specific
- CRISPRClustered regularly interspaced short palindromic repeats (CRISPR) is a prokaryotic adaptive immune response that provides immunity against foreign nucleic acids, such as viral DNA and bacterial plasmids, through the use of crRNAs (CRISPR RNAs) and associated Cas genes.
- CRISPR-Cas9CRISPR-Cas9 is a genome editing system. CRISPR systems provides immunity to bacteria and archaea from viruses and has been adapted for use as a genome editing tool capable of knocking out genes and rewriting genetic sequences in animal, plant and fungi. CRISPR-Cas9 is being adapted to other applications outside genome editing.
- CRISPR-Cas12aCRISPR-Cas12a is is a genome editing tool similar to CRISPR-Cas9. CRISPR-Cas12a is a set of RNA guided DNA targeting proteins capable of producing targeted double-stranded DNA (dsDNA) breaks, targeted single-stranded DNA breaks, and indiscriminate ssDNA degradation in trans. The effector protein Cas12a is also known at Cpf1.