Structure of Csm2 elucidates the relationship between small subunits of CRISPR-Cas effector complexes

FEBS Lett. 2016 May;590(10):1521-9. doi: 10.1002/1873-3468.12179. Epub 2016 May 5.


Type I and type III CRISPR-Cas effector complexes share similar architecture and have homologous key subunits. However, the relationship between the so-called small subunits of these complexes remains a contentious issue. Here, it is shown that the recently solved structure of Thermotoga maritima Csm2 represents a dimer with the extensive structure swapping between monomers. Unswapping the structure generates a compact globular monomer which shares similar structure and surface properties with Cmr5, the small subunit of a related Cmr complex. Detailed analysis of available structures of small subunits reveals that they all have a common fold suggesting their common origin.

Keywords: CRISPR-Cas; Csm2; protein fold; protein homology; small subunits; structural similarity.

Publication types

  • Letter

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism
  • CRISPR-Associated Proteins / chemistry*
  • CRISPR-Associated Proteins / metabolism*
  • CRISPR-Cas Systems
  • Models, Molecular
  • Protein Multimerization
  • Protein Structure, Secondary
  • Thermotoga maritima / chemistry
  • Thermotoga maritima / metabolism*


  • Bacterial Proteins
  • CRISPR-Associated Proteins