Current Updates of CRISPR/Cas System and Anti-CRISPR Proteins: Innovative Applications to Improve the Genome Editing Strategies.

The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated sequence (CRISPR/Cas) system is a cutting-edge genome-editing tool employed to explore the functions of normal and disease-related genes. The CRISPR/Cas system has a remarkable diversity in the composition and architecture of genomic loci and Cas protein sequences. Owing to its excellent efficiency and specificity, this system adds an outstanding dimension to biomedical research on genetic manipulation of eukaryotic cells. However, safe, efficient, and specific delivery of this system to target cells and tissues and their off-target effects are considered critical bottlenecks for the therapeutic applications. Recently discovered anti-CRISPR proteins (Acr) play a significant role in limiting the effects of this system. Acrs are relatively small proteins that are highly specific to CRISPR variants and exhibit remarkable structural diversity. The in silico approaches, crystallography, and cryo-electron microscopy play significant roles in elucidating the mechanisms of action of Acrs. Acrs block the CRISPR/Cas system mainly by employing four mechanisms: CRISPR/Cas complex assembly interruption, target-binding interference, target cleavage prevention, and degradation of cyclic oligonucleotide signaling molecules. Engineered CRISPR/Cas systems are frequently used in gene therapy, diagnostics, and functional genomics. Understanding the molecular mechanisms underlying Acr action may help in the safe and effective use of CRISPR/Cas tools for genetic modification, particularly in the context of medicine. Thus, attempts to regulate prokaryotic CRISPR/Cas surveillance complexes will advance the development of antimicrobial drugs and treatment of human diseases. In this review, recent updates on CRISPR/Cas systems, especially CRISPR/Cas9 and Acrs, and their novel mechanistic insights are elaborated. In addition, the role of Acrs in the novel applications of CRISPP/Cas biotechnology for precise genome editing and other applications is discussed.