8d3m
From Proteopedia
Type I-C Cas4-Cas1-Cas2 complex bound to a PAM/Processed prespacer
Structural highlights
FunctionQ9KFX9_HALH5 CRISPR (clustered regularly interspaced short palindromic repeat), is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain spacers, sequences complementary to antecedent mobile elements, and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). Acts as a dsDNA endonuclease. Involved in the integration of spacer DNA into the CRISPR cassette.[HAMAP-Rule:MF_01470] Publication Abstract from PubMedAdaptation 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. We determined 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. Corroborated with our biochemical results, Cas4-Cas1-Cas2 structures with substrates representing various stages of CRISPR adaptation reveal a temporally resolved mechanism for maturation and integration of functional spacers into the CRISPR array. PAM binding ensures orientational integration during Cas4-Cas1-Cas2-mediated CRISPR adaptation.,Dhingra Y, Suresh SK, Juneja P, Sashital DG Mol Cell. 2022 Nov 17;82(22):4353-4367.e6. doi: 10.1016/j.molcel.2022.09.030. , Epub 2022 Oct 21. PMID:36272411[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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