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Publication Abstract from PubMed

CRISPR-Cas systems are adaptive immune systems that protect prokaryotes from foreign nucleic acids, such as bacteriophages. Two of the most prevalent CRISPR-Cas systems include type I and type III. Interestingly, the type I-D interference proteins contain characteristic features of both type I and type III systems. Here, we present the structures of type I-D Cascade bound to both a double-stranded (ds)DNA and a single-stranded (ss)RNA target at 2.9 and 3.1 A, respectively. We show that type I-D Cascade is capable of specifically binding ssRNA and reveal how PAM recognition of dsDNA targets initiates long-range structural rearrangements that likely primes Cas10d for Cas3' binding and subsequent non-target strand DNA cleavage. These structures allow us to model how binding of the anti-CRISPR protein AcrID1 likely blocks target dsDNA binding via competitive inhibition of the DNA substrate engagement with the Cas10d active site. This work elucidates the unique mechanisms used by type I-D Cascade for discrimination of single-stranded and double stranded targets. Thus, our data supports a model for the hybrid nature of this complex with features of type III and type I systems.

Structural rearrangements allow nucleic acid discrimination by type I-D Cascade.,Schwartz EA, McBride TM, Bravo JPK, Wrapp D, Fineran PC, Fagerlund RD, Taylor DW Nat Commun. 2022 May 20;13(1):2829. doi: 10.1038/s41467-022-30402-8. PMID:35595728^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.