Anti‐CRISPR proteins targeting the CRISPR‐Cas system enrich the toolkit for genetic engineering

Abstract

Clustered regularly interspaced short palindromic repeats (CRISPR)‐Cas adaptive immune defense systems, which are widely distributed in bacteria and Archaea, can provide sequence‐specific protection against foreign DNA or RNA in some cases. However, the evolution of defense systems in bacterial hosts did not lead to the elimination of phages, and some phages carry anti‐CRISPR genes that encode products that bind to the components mediating the defense mechanism and thus antagonize CRISPR‐Cas immune systems of bacteria. Given the extensive application of CRISPR‐Cas9 technologies in gene editing, in this review, we focus on the anti‐CRISPR proteins (Acrs) that inhibit CRISPR‐Cas systems for gene editing. We describe the discovery of Acrs in immune systems involving type I, II, and V CRISPR‐Cas immunity, discuss the potential function of Acrs in inactivating type II and V CRISPR‐Cas systems for gene editing and gene modulation, and provide an outlook on the development of important biotechnology tools for genetic engineering using Acrs.

Types I and V Anti-CRISPR Proteins: From Phage Defense to Eukaryotic Synthetic Gene Circuits

“…To date, 30 distinct families of anti-CRISPR proteins have been identified for type I and type V-A systems (Liu et al, 2020). Thirteen of them manifested on CRISPR-Cas an inhibitory action that is carried out in two different ways: either by preventing the Cascade/Cas-crRNA complex from binding the substrate DNA or by blocking DNA cleavage after inactivating the Cas effector.…”

“…Over half of the anti-CRISPR proteins so far reported in the literature belong to type I. Overall, there are 25 AcrI families (Hwang and Maxwell, 2019;Zhang F. et al, 2019;Liu et al, 2020): 14 from subtype F (AcrIF1-F14), 7 from subtype E (AcrIE1-E7), and one apiece from subtype B, C and D. Moreover, the chimeric AcrIE4-F7 shows a dual type inhibition combining those of type I-E and type I-F. It is worth mentioning that AcrIF6 inhibits CRISPR-Cas type I-E as well.…”

“…In this context, phages further modified their genome to escape from being targeted by CRISPR-Cas immune system ( Samson et al, 2013 ) and the anti-CRISPR proteins (Acrs) made their appearance ( Pawluk et al, 2018 ). Anti-CRISPRs are small proteins (approximately, 12–193 amino acids) that confer to phages an efficient and powerful means to nullify the CRISPR-Cas immune system ( Liu et al, 2020 ).…”

Diversity of molecular mechanisms used by anti-CRISPR proteins: the tip of an iceberg?

“…In recent years, the highly dynamic anti-CRISPR field of research has emerged and accumulated important knowledge on the molecular mechanisms deployed by these natural CRISPR-Cas inhibitors. Many reviews that thoroughly present the discovery of anti-CRISPR proteins and their molecular mechanisms have recently been published [11,[15][16][17]. Here, we intend to provide a complementary, global perspective on their mode of action.…”

CRISPR: development of a technology and its applications

“…However, like all biological arms races the phage has learned how to neutralize the Cas nuclease with anti-CRISPR proteins [8]. In their Minireview, Liu et al [9] cover the growing list of anti-CRISPR proteins and the distinct ways they inhibit the Cas nucleases. There are many potential applications for the use of anti-CRISPRs in biology and medicine, for example, to rapidly shut the nuclease activity of Cas proteins off to reduce potential off-target mutations.…”