3s4l
The CRISPR-associated Cas3 HD domain protein MJ0384 from Methanocaldococcus jannaschiiThe CRISPR-associated Cas3 HD domain protein MJ0384 from Methanocaldococcus jannaschii
Structural highlights
Function[CS3HD_METJA] 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). Cas3 plus Cascade participate in CRISPR interference, the third stage of CRISPR immunity. Acts as a ssDNA and ssRNA nuclease, with both endo- and 3' to 5' exonuclease activities, acting on substrates with free single-stranded 3' ends. Double-stranded nucleic acids are not substrates. Activity is higher for DNA than RNA. Templates include R-loops (a bubble-like structure formed when ssRNA replaces one strand in a dsDNA, such as crRNA is thought to form with CRISPR target DNA), circular ssDNA, 2',3'-cAMP and 2',3'-cGMP. Probably generates 3'-phosphate and 5'-hydroxyl ends. In the presence of the Cas3 helicase and ATP dsDNA templates are also degraded.[1] Publication Abstract from PubMedClustered regularly interspaced short palindromic repeats (CRISPRs) and Cas proteins represent an adaptive microbial immunity system against viruses and plasmids. Cas3 proteins have been proposed to play a key role in the CRISPR mechanism through the direct cleavage of invasive DNA. Here, we show that the Cas3 HD domain protein MJ0384 from Methanocaldococcus jannaschii cleaves endonucleolytically and exonucleolytically (3'-5') single-stranded DNAs and RNAs, as well as 3'-flaps, splayed arms, and R-loops. The degradation of branched DNA substrates by MJ0384 is stimulated by the Cas3 helicase MJ0383 and ATP. The crystal structure of MJ0384 revealed the active site with two bound metal cations and together with site-directed mutagenesis suggested a catalytic mechanism. Our studies suggest that the Cas3 HD nucleases working together with the Cas3 helicases can completely degrade invasive DNAs through the combination of endo- and exonuclease activities. Structure and activity of the Cas3 HD nuclease MJ0384, an effector enzyme of the CRISPR interference.,Beloglazova N, Petit P, Flick R, Brown G, Savchenko A, Yakunin AF EMBO J. 2011 Oct 18;30(22):4616-27. doi: 10.1038/emboj.2011.377. PMID:22009198[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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