The gRAMP CRISPR-Cas effector is an RNA endonuclease complexed with a caspase-like peptidase
S.P.B. van Beljouw (TU Delft - Applied Sciences)
A.C. van Eijkeren-Haagsma (Kavli institute of nanoscience Delft, TU Delft - BN/Technici en Analisten)
A. Rodriguez Molina (Kavli institute of nanoscience Delft, TU Delft - Applied Sciences)
D.F. van den Berg (External organisation, Kavli institute of nanoscience Delft)
J.N.A. Vink (Kavli institute of nanoscience Delft, TU Delft - Applied Sciences)
S.J.J. Brouns (Kavli institute of nanoscience Delft, TU Delft - Applied Sciences)
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Abstract
Type III CRISPR-Cas immunity is widespread in prokaryotes and is generally mediated by multisubunit effector complexes. These complexes recognize complementary viral transcripts and can activate ancillary immune proteins. Here, we describe a type III-E effector from Candidatus “Scalindua brodae” (Sb-gRAMP), which is natively encoded by a single gene with several type III domains fused together. This effector uses CRISPR RNA to guide target RNA recognition and cleaves single-stranded RNA at two defined positions six nucleotides apart. Sb-gRAMP physically combines with the caspase-like TPR-CHAT peptidase to form the CRISPR-guided caspase (Craspase) complex, suggesting a potential mechanism of target RNA-induced protease activity to gain viral immunity.