Structure of Can2 from Sulfobacillus thermosulfidooxidans in complex with cyclic tetra-adenylate (cA4)

Experimental Data Snapshot

  • Resolution: 2.02 Å
  • R-Value Free: 0.290 
  • R-Value Work: 0.241 
  • R-Value Observed: 0.243 

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This is version 2.0 of the entry. See complete history


The CRISPR ancillary effector Can2 is a dual-specificity nuclease potentiating type III CRISPR defence.

Zhu, W.McQuarrie, S.Gruschow, S.McMahon, S.A.Graham, S.Gloster, T.M.White, M.F.

(2021) Nucleic Acids Res 49: 2777-2789

  • DOI: https://doi.org/10.1093/nar/gkab073
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Cells and organisms have a wide range of mechanisms to defend against infection by viruses and other mobile genetic elements (MGE). Type III CRISPR systems detect foreign RNA and typically generate cyclic oligoadenylate (cOA) second messengers that bind to ancillary proteins with CARF (CRISPR associated Rossman fold) domains. This results in the activation of fused effector domains for antiviral defence. The best characterised CARF family effectors are the Csm6/Csx1 ribonucleases and DNA nickase Can1. Here we investigate a widely distributed CARF family effector with a nuclease domain, which we name Can2 (CRISPR ancillary nuclease 2). Can2 is activated by cyclic tetra-adenylate (cA4) and displays both DNase and RNase activity, providing effective immunity against plasmid transformation and bacteriophage infection in Escherichia coli. The structure of Can2 in complex with cA4 suggests a mechanism for the cA4-mediated activation of the enzyme, whereby an active site cleft is exposed on binding the activator. These findings extend our understanding of type III CRISPR cOA signalling and effector function.

  • Organizational Affiliation

    Biomedical Sciences Research Complex, School of Biology, University of St Andrews, St Andrews KY16 9ST, UK.


Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B, C, D
366Sulfobacillus thermosulfidooxidansMutation(s): 0 
Find proteins for A0A8I3AZU2 (Sulfobacillus thermosulfidooxidans)
Explore A0A8I3AZU2 
Go to UniProtKB:  A0A8I3AZU2
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupA0A8I3AZU2
Sequence Annotations
  • Reference Sequence

Find similar nucleic acids by:  Sequence   |   3D Structure  

Entity ID: 2
MoleculeChains LengthOrganismImage
Cyclic tetraadenosine monophosphate (cA4)E [auth F],
F [auth H]
4synthetic construct
Sequence Annotations
  • Reference Sequence
Small Molecules
Modified Residues  1 Unique
IDChains TypeFormula2D DiagramParent
Query on MSE
A, B, C, D
Biologically Interesting Molecules (External Reference) 1 Unique
Experimental Data & Validation

Experimental Data

  • Resolution: 2.02 Å
  • R-Value Free: 0.290 
  • R-Value Work: 0.241 
  • R-Value Observed: 0.243 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 75.86α = 90
b = 85.97β = 90
c = 237.91γ = 90
Software Package:
Software NamePurpose
XDSdata reduction
Aimlessdata scaling
PDB_EXTRACTdata extraction
Cootmodel building

Structure Validation

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Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
Biotechnology and Biological Sciences Research Council (BBSRC)United KingdomBB/T004789/1
Biotechnology and Biological Sciences Research Council (BBSRC)United KingdomBB/S000313/1
Wellcome TrustUnited Kingdom204821/Z/16/Z
Chinese Academy of SciencesChina201703780015

Revision History  (Full details and data files)

  • Version 1.0: 2021-03-03
    Type: Initial release
  • Version 1.1: 2021-03-31
    Changes: Database references
  • Version 2.0: 2023-12-13
    Changes: Advisory, Atomic model, Data collection, Database references, Derived calculations, Refinement description, Structure summary