RT Journal Article
SR Electronic
T1 AcrIIA22 is a novel anti-CRISPR that impairs SpyCas9 activity by relieving DNA torsion of target plasmids
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.09.28.317578
DO 10.1101/2020.09.28.317578
A1 Forsberg, Kevin J.
A1 Schmidtke, Danica T.
A1 Werther, Rachel
A1 Hausman, Deanna
A1 Stoddard, Barry L.
A1 Kaiser, Brett K.
A1 Malik, Harmit S.
YR 2020
UL http://biorxiv.org/content/early/2020/09/29/2020.09.28.317578.abstract
AB To overcome CRISPR-Cas defense systems, many phages and mobile genetic elements encode CRISPR-Cas inhibitors called anti-CRISPRs (Acrs). Nearly all mechanistically characterized Acrs directly bind their cognate Cas protein to inactivate CRISPR immunity. Here, we describe AcrIIA22, an unconventional Acr found in hypervariable genomic regions of Clostridial bacteria and their prophages from the human gut microbiome. Uncovered in a functional metagenomic selection, AcrIIA22 does not bind strongly to SpyCas9 but nonetheless potently inhibits its activity against plasmids. To gain insight into its mechanism, we obtained an X-ray crystal structure of AcrIIA22, which revealed homology to PC4-like nucleic-acid binding proteins. This homology helped us deduce that acrIIA22 encodes a DNA nickase that relieves torsional stress in supercoiled plasmids, rendering them less susceptible to SpyCas9, which is highly dependent on negative supercoils to form stable R-loops. Modifying DNA topology may provide an additional route to CRISPR-Cas resistance in phages and mobile genetic elements.Competing Interest StatementThe authors have declared no competing interest.