9FCV

Cas nuclease-CRISPR (cr)RNA ribonucleoprotein (RNP) complex

Summary for 9FCV

• Entry DOI: 10.2210/pdb9fcv/pdb
• EMDB information: 50322
• Descriptor: Phage head-tail adaptor, crRNA (2 entities in total)
• Functional Keywords: acrvib1; anti-crispr protein; cas13b, rna binding protein
• Biological source: Segatella buccae; More
• Total number of polymer chains: 2
• Total formula weight: 160181.29

Authors

Schmelz, S.,Lukat, P.,Blankenfeldt, W. (deposition date: 2024-05-16, release date: 2025-02-12, Last modification date: 2025-04-02)

Primary citation

Wandera, K.G.,Schmelz, S.,Migur, A.,Kibe, A.,Lukat, P.,Achmedov, T.,Caliskan, N.,Blankenfeldt, W.,Beisel, C.L.
AcrVIB1 inhibits CRISPR-Cas13b immunity by promoting unproductive crRNA binding accessible to RNase attack.
Mol.Cell, 85:1162-, 2025

PubMed Abstract: Anti-CRISPR proteins (Acrs) inhibit CRISPR-Cas immune defenses, with almost all known Acrs acting on the Cas nuclease-CRISPR (cr)RNA ribonucleoprotein (RNP) complex. Here, we show that AcrVIB1 from Riemerella anatipestifer, the only known Acr against Cas13b, principally acts upstream of RNP complex formation by promoting unproductive crRNA binding followed by crRNA degradation. AcrVIB1 tightly binds to Cas13b but not to the Cas13b-crRNA complex, resulting in enhanced rather than blocked crRNA binding. However, the more tightly bound crRNA does not undergo processing and fails to activate collateral RNA cleavage even with target RNA. The bound crRNA is also accessible to RNases, leading to crRNA turnover in vivo even in the presence of Cas13b. Finally, cryoelectron microscopy (cryo-EM) structures reveal that AcrVIB1 binds a helical domain of Cas13b responsible for securing the crRNA, keeping the domain untethered. These findings reveal an Acr that converts an effector nuclease into a crRNA sink to suppress CRISPR-Cas defense.

PubMed: 39965569
DOI: 10.1016/j.molcel.2025.01.020

Experimental method

ELECTRON MICROSCOPY (3.09 Å)