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Publication Abstract from PubMed

The Clusters of Regularly Interspaced Short Palindromic Repeats (CRISPR) and the Cas (CRISPR-associated) proteins form an adaptive immune system in bacteria and archaea that evolved as an RNA-guided interference mechanism to target and degrade foreign genetic elements. In the so called type IIIA CRISPR-Cas systems, Cas proteins from the Csm family form a complex of ribonucleoproteins (RNPs) that are involved in surveillance and targeting tasks. Here we report the crystal structure of Thermotoga maritima Csm2. This protein is thought to assemble into the helically shaped Csm RNP complex in a site opposite to the crRNA (CRISPR RNA) binding backbone. Csm2 was solved via Cadmium Single Wavelength Anomalous Diffraction (Cd-SAD) phasing at 2.4 A resolution. The structure reveals that Csm2 is composed of a large 42 amino-acid long alpha-helix flanked by three shorter alpha-helices. The structure also shows that the protein is capable of forming dimers mainly via an extensive contact surface conferred by its long alpha-helix. This interaction is further stabilized by the N-terminal helix, which is inserted into the C-terminal helical portion of the adjacent subunit. The dimerization of Csm2 was additionally confirmed by size exclusion chromatography of the pure recombinant protein followed by mass spectrometry analysis of the eluted fractions. Due to its role in the assembling and functioning of the Csm crRNP complex, the crystal structure of Csm2 is of great importance to elucidating the mechanism of action of the subtype IIIA CRISPR-Cas system, as well as the similarities and diversities between the different CRISPR/Cas systems. This article is protected by copyright. All rights reserved.

Structural basis for dimer formation of the CRISPR-associated protein Csm2 of Thermotoga maritima.,Gallo G, Augusto G, Rangel G, Zelanis A, Mori MA, Campos CB, Wurtele M FEBS J. 2015 Dec 10. doi: 10.1111/febs.13621. PMID:26663887^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.