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Crystal Structure of Cas-DNA-PAM complex
Structural highlights
FunctionCAS1_ECOLI 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 sequences complementary to antecedent mobile elements and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). Cas1 is thought to be involved in CRISPR adaptation, the first stage of CRISPR immunity. Might be involved in the addition/removal of CRISPR spacers. Endonucleolytically cleaves linear ssRNA, ssDNA and short (34 base) dsDNA as well as branched DNA substrates such as Holliday junctions, replication forks and 5'-flap DNA substrates. Genetic interactions suggest Cas1 interacts with components of the RecBC and RuvB DNA repair systems.[1] Publication Abstract from PubMedBacteria acquire memory of viral invaders by incorporating invasive DNA sequence elements into the host CRISPR locus, generating a new spacer within the CRISPR array. We report on the structures of Cas1-Cas2-dual-forked DNA complexes in an effort toward understanding how the protospacer is sampled prior to insertion into the CRISPR locus. Our study reveals a protospacer DNA comprising a 23-bp duplex bracketed by tyrosine residues, together with anchored flanking 3' overhang segments. The PAM-complementary sequence in the 3' overhang is recognized by the Cas1a catalytic subunits in a base-specific manner, and subsequent cleavage at positions 5 nt from the duplex boundary generates a 33-nt DNA intermediate that is incorporated into the CRISPR array via a cut-and-paste mechanism. Upon protospacer binding, Cas1-Cas2 undergoes a significant conformational change, generating a flat surface conducive to proper protospacer recognition. Here, our study provides important structure-based mechanistic insights into PAM-dependent spacer acquisition. Structural and Mechanistic Basis of PAM-Dependent Spacer Acquisition in CRISPR-Cas Systems.,Wang J, Li J, Zhao H, Sheng G, Wang M, Yin M, Wang Y Cell. 2015 Nov 5;163(4):840-53. doi: 10.1016/j.cell.2015.10.008. Epub 2015 Oct, 17. PMID:26478180[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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