Broad-spectrum anti-CRISPR proteins facilitate horizontal gene transfer

Nat Microbiol. 2020 Apr;5(4):620-629. doi: 10.1038/s41564-020-0692-2. Epub 2020 Mar 26.

Abstract

CRISPR-Cas adaptive immune systems protect bacteria and archaea against their invading genetic parasites, including bacteriophages/viruses and plasmids. In response to this immunity, many phages have anti-CRISPR (Acr) proteins that inhibit CRISPR-Cas targeting. To date, anti-CRISPR genes have primarily been discovered in phage or prophage genomes. Here, we uncovered acr loci on plasmids and other conjugative elements present in Firmicutes using the Listeria acrIIA1 gene as a marker. The four identified genes, found in Listeria, Enterococcus, Streptococcus and Staphylococcus genomes, can inhibit type II-A SpyCas9 or SauCas9, and are thus named acrIIA16-19. In Enterococcus faecalis, conjugation of a Cas9-targeted plasmid was enhanced by anti-CRISPRs derived from Enterococcus conjugative elements, highlighting a role for Acrs in the dissemination of plasmids. Reciprocal co-immunoprecipitation showed that each Acr protein interacts with Cas9, and Cas9-Acr complexes were unable to cleave DNA. Northern blotting suggests that these anti-CRISPRs manipulate single guide RNA length, loading or stability. Mirroring their activity in bacteria, AcrIIA16 and AcrIIA17 provide robust and highly potent broad-spectrum inhibition of distinct Cas9 proteins in human cells (for example, SpyCas9, SauCas9, SthCas9, NmeCas9 and CjeCas9). This work presents a focused analysis of non-phage Acr proteins, demonstrating a role in horizontal gene transfer bolstered by broad-spectrum CRISPR-Cas9 inhibition.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • CRISPR-Associated Protein 9 / antagonists & inhibitors*
  • CRISPR-Associated Protein 9 / genetics
  • CRISPR-Associated Protein 9 / metabolism
  • CRISPR-Cas Systems*
  • Clustered Regularly Interspaced Short Palindromic Repeats
  • Conjugation, Genetic
  • DNA / antagonists & inhibitors
  • DNA / genetics
  • DNA / metabolism
  • Enterococcus / genetics
  • Enterococcus / virology
  • Gene Transfer, Horizontal*
  • HEK293 Cells
  • Humans
  • Listeria / genetics
  • Listeria / virology
  • Plasmids / chemistry
  • Plasmids / metabolism*
  • Protein Binding
  • RNA, Guide, CRISPR-Cas Systems / antagonists & inhibitors*
  • RNA, Guide, CRISPR-Cas Systems / genetics
  • RNA, Guide, CRISPR-Cas Systems / metabolism
  • Staphylococcus / genetics
  • Staphylococcus / virology
  • Streptococcus / genetics
  • Streptococcus / virology

Substances

  • RNA, Guide, CRISPR-Cas Systems
  • DNA
  • CRISPR-Associated Protein 9