8DEX

type I-C Cascade

Summary for 8DEX

• Entry DOI: 10.2210/pdb8dex/pdb
• EMDB information: 27402
• Descriptor: pre-crRNA processing endonuclease, CRISPR-associated protein, TM1801 family, CRISPR-associated protein, CT1133 family, ... (5 entities in total)
• Functional Keywords: type i-c, crispr, cascade, dna binding protein, rna binding protein-rna complex, rna binding protein/rna
• Biological source: Desulfovibrio vulgaris; More
• Total number of polymer chains: 12
• Total formula weight: 364125.69

Authors

O'Brien, R.E.,Bravo, J.P.K.,Ramos, D.,Hibshman, G.N.,Wright, J.T.,Taylor, D.W. (deposition date: 2022-06-21, release date: 2023-02-15, Last modification date: 2025-06-04)

Primary citation

O'Brien, R.E.,Bravo, J.P.K.,Ramos, D.,Hibshman, G.N.,Wright, J.T.,Taylor, D.W.
Structural snapshots of R-loop formation by a type I-C CRISPR Cascade.
Mol.Cell, 83:746-, 2023

PubMed Abstract: Type I CRISPR-Cas systems employ multi-subunit Cascade effector complexes to target foreign nucleic acids for destruction. Here, we present structures of D. vulgaris type I-C Cascade at various stages of double-stranded (ds)DNA target capture, revealing mechanisms that underpin PAM recognition and Cascade allosteric activation. We uncover an interesting mechanism of non-target strand (NTS) DNA stabilization via stacking interactions with the "belly" subunits, securing the NTS in place. This "molecular seatbelt" mechanism facilitates efficient R-loop formation and prevents dsDNA reannealing. Additionally, we provide structural insights into how two anti-CRISPR (Acr) proteins utilize distinct strategies to achieve a shared mechanism of type I-C Cascade inhibition by blocking PAM scanning. These observations form a structural basis for directional R-loop formation and reveal how different Acr proteins have converged upon common molecular mechanisms to efficiently shut down CRISPR immunity.

PubMed: 36805026
DOI: 10.1016/j.molcel.2023.01.024

Experimental method

ELECTRON MICROSCOPY (2.7 Å)