Adaptation in CRISPR-Cas systems immunizes bacteria and archaea against mobile genetic elements. In many DNA-targeting systems, the Cas4-Cas1-Cas2 complex is required for selection and processing of DNA segments containing PAM sequences prior to integration of these “prespacer” substrates as spacers in the CRISPR array. A recent paper published in Molecular Cell journal determined the cryo-EM structures of the Cas4-Cas1-Cas2 adaptation complex from the type I-C system that encodes standalone Cas1 and Cas4 proteins. The structures reveal how Cas4 specifically reads out bases within the PAM sequence and how interactions with both Cas1 and Cas2 activate Cas4 endonuclease activity. The Cas4-PAM interaction ensures tight binding between the adaptation complex and the prespacer, significantly enhancing integration of the non-PAM end into the CRISPR array and ensuring correct spacer orientation. Here you can see an equatorial view of the complex showing the binding of the Cas elements to the PAM/PAM prespacer (PDB code: 8D3L)
#molecularart ... #immolecular ... #crispr ... #cas ... #prespacer ... #complex ... #integration ... #cryoem
Structure rendered with @proteinimaging and depicted with @corelphotopaint
#molecularart ... #immolecular ... #crispr ... #cas ... #prespacer ... #complex ... #integration ... #cryoem
Structure rendered with @proteinimaging and depicted with @corelphotopaint
