Journal
CELL
Volume 185, Issue 22, Pages 4067-+Publisher
CELL PRESS
DOI: 10.1016/j.cell.2022.09.026
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Funding
- Swiss National Science Foundation [31003A_182567]
- National Institutes of Health [R01GM141329]
- National Science Foundation [CHE-1905374]
- International Research Scholar of the Howard Hughes Medical Institute
- Vallee Scholar of the Bert L & N Kuggie Vallee Foundation
- Swiss National Science Foundation (SNF) [31003A_182567] Funding Source: Swiss National Science Foundation (SNF)
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The crystallographic structures of Cas9 bound to off-target substrates reveal that noncanonical base-pairing interactions within the guide:off-target heteroduplex enable off-target binding. Single-nucleotide deletions in off-target substrates are accommodated by base skipping or multiple noncanonical base pairs. PAM-distal mismatches result in duplex unpairing and induce a conformational change in the Cas9 REC lobe. These insights contribute to the improved rational design of guide RNAs and off-target prediction algorithms.
The target DNA specificity of the CRISPR-associated genome editor nuclease Cas9 is determined by complementarity to a 20-nucleotide segment in its guide RNA. However, Cas9 can bind and cleave partially complementary off-target sequences, which raises safety concerns for its use in clinical applications. Here, we report crystallographic structures of Cas9 bound to bona fide off-target substrates, revealing that off -target binding is enabled by a range of noncanonical base-pairing interactions within the guide:off-target heteroduplex. Off-target substrates containing single-nucleotide deletions relative to the guide RNA are accommodated by base skipping or multiple noncanonical base pairs rather than RNA bulge formation. Finally, PAM-distal mismatches result in duplex unpairing and induce a conformational change in the Cas9 REC lobe that perturbs its conformational activation. Together, these insights provide a structural rationale for the off-target activity of Cas9 and contribute to the improved rational design of guide RNAs and off-target prediction algorithms.
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