8PCW

Structure of Csm6' from Streptococcus thermophilus

Summary for 8PCW

• Entry DOI: 10.2210/pdb8pcw/pdb
• Related: 8PE3
• Descriptor: CRISPR system endoribonuclease Csm6' (1 entity in total)
• Functional Keywords: carf, hepn, ca6, rnase, rna binding protein
• Biological source: Streptococcus thermophilus
• Total number of polymer chains: 2
• Total formula weight: 90208.57

Authors

McQuarrie, S.J.,Athukoralage, J.S.,McMahon, S.A.,Graham, S.,Ackerman, K.,Bode, B.E.,White, M.F.,Gloster, T.M. (deposition date: 2023-06-11, release date: 2023-10-04, Last modification date: 2023-11-08)

Primary citation

McQuarrie, S.,Athukoralage, J.S.,McMahon, S.A.,Graham, S.,Ackermann, K.,Bode, B.E.,White, M.F.,Gloster, T.M.
Activation of Csm6 ribonuclease by cyclic nucleotide binding: in an emergency, twist to open.
Nucleic Acids Res., 51:10590-10605, 2023

PubMed Abstract: Type III CRISPR systems synthesize cyclic oligoadenylate (cOA) second messengers as part of a multi-faceted immune response against invading mobile genetic elements (MGEs). cOA activates non-specific CRISPR ancillary defence nucleases to create a hostile environment for MGE replication. Csm6 ribonucleases bind cOA using a CARF (CRISPR-associated Rossmann Fold) domain, resulting in activation of a fused HEPN (Higher Eukaryotes and Prokaryotes Nucleotide binding) ribonuclease domain. Csm6 enzymes are widely used in a new generation of diagnostic assays for the detection of specific nucleic acid species. However, the activation mechanism is not fully understood. Here we characterised the cyclic hexa-adenylate (cA6) activated Csm6' ribonuclease from the industrially important bacterium Streptococcus thermophilus. Crystal structures of Csm6' in the inactive and cA6 bound active states illuminate the conformational changes which trigger mRNA destruction. Upon binding of cA6, there is a close to 60° rotation between the CARF and HEPN domains, which causes the 'jaws' of the HEPN domain to open and reposition active site residues. Key to this transition is the 6H domain, a right-handed solenoid domain connecting the CARF and HEPN domains, which transmits the conformational changes for activation.

PubMed: 37747760
DOI: 10.1093/nar/gkad739

Experimental method

X-RAY DIFFRACTION (3.54 Å)