The crystal structure of the CRISPR-associated protein Csn2 from Streptococcus agalactiae |
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Authors: | Ellinger Philipp Arslan Zihni Wurm Reinhild Tschapek Britta MacKenzie Colin Pfeffer Klaus Panjikar Santosh Wagner Rolf Schmitt Lutz Gohlke Holger Pul Ümit Smits Sander H J |
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Institution: | Institute of Biochemistry, Heinrich Heine University, Universit?tsstr. 1, 40225 Düsseldorf, Germany. |
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Abstract: | The prokaryotic immune system, CRISPR, confers an adaptive and inheritable defense mechanism against invasion by mobile genetic elements. Guided by small CRISPR RNAs (crRNAs), a diverse family of CRISPR-associated (Cas) proteins mediates the targeting and inactivation of foreign DNA. Here, we demonstrate that Csn2, a Cas protein likely involved in spacer integration, forms a tetramer in solution and structurally possesses a ring-like structure. Furthermore, co-purified Ca(2+) was found important for the DNA binding property of Csn2, which contains a helicase fold, with highly conserved DxD and RR motifs found throughout Csn2 proteins. We could verify that Csn2 binds ds-DNA. In addition molecular dynamics simulations suggested a Csn2 conformation that can "sit" on the DNA helix and binds DNA in a groove on the outside of the ring. |
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