4ic1
From Proteopedia
Crystal structure of SSO0001
Structural highlights
FunctionCAS4_SACS2 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) (By similarity). This protein is a 5' to 3' partially processive exonuclease that cleaves off single mononucleotides. Has a marked preference for ssDNA, although in vitro it also acts on dsDNA and ssRNA. Has low endonuclease activity with circular ssDNA. Binds ssDNA and can unwind dsDNA; unwinding does not require ATP.[1] [2] Publication Abstract from PubMedCas4 proteins, a core protein family associated with the microbial system of adaptive immunity CRISPR, are predicted to function in the adaptation step of the CRISPR mechanism. Here we show that the Cas4 protein SSO0001 from the archaeon Sulfolobus solfataricus has metal-dependent endonuclease and 5'-->3' exonuclease activities against single-stranded DNA, as well as ATP-independent DNA unwinding activity toward double-stranded DNA. The crystal structure of SSO0001 revealed a decameric toroid formed by five dimers with each protomer containing one [4Fe-4S] cluster and one Mn(2+) ion bound in the active site located inside the internal tunnel. The conserved RecB motif and four Cys residues are important for DNA binding and cleavage activities, whereas DNA unwinding depends on several residues located near the [4Fe-4S] cluster. Our results suggest that Cas4 proteins might contribute to the addition of novel CRISPR spacers through the formation of 3'-DNA overhangs and to the degradation of foreign DNA. Toroidal structure and DNA cleavage by the CRISPR-associated [4Fe-4S] cluster containing Cas4 nuclease SSO0001 from Sulfolobus solfataricus.,Lemak S, Beloglazova N, Nocek B, Skarina T, Flick R, Brown G, Popovic A, Joachimiak A, Savchenko A, Yakunin AF J Am Chem Soc. 2013 Nov 20;135(46):17476-87. doi: 10.1021/ja408729b. Epub 2013, Nov 11. PMID:24171432[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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