title: Structural biology. Crystal structure of a CRISPR RNA-guided surveillance complex bound to a ssDNA target.
abstract: In prokaryotes, RNA derived from type I and type III CRISPR loci direct large ribonucleoprotein complexes to destroy invading bacteriophage and plasmids. In Escherichia coli, this 405-kilodalton complex is called Cascade. We report the crystal structure of Cascade bound to a single-stranded DNA (ssDNA) target at a resolution of 3.03 angstroms. The structure reveals that the CRISPR RNA and target strands do not form a double helix but instead adopt an underwound ribbon-like structure. This noncanonical structure is facilitated by rotation of every sixth nucleotide out of the RNA-DNA hybrid and is stabilized by the highly interlocked organization of protein subunits. These studies provide insight into both the assembly and the activity of this complex and suggest a mechanism to enforce fidelity of target binding.
authors.affiliation: Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205, USA.
authors.forename: Sabin
authors.initials: S
authors.lastname: Mulepati
authors.affiliation: Photon Sciences Directorate, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Annie
authors.initials: A
authors.lastname: Héroux
authors.affiliation: Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205, USA. scott.bailey@jhu.edu.
authors.forename: Scott
authors.initials: S
authors.lastname: Bailey
mesh_terms: D064130:CRISPR-Associated Proteins / Q000737:chemistry*; D064113:CRISPR-Cas Systems; D064112:Clustered Regularly Interspaced Short Palindromic Repeats; D018360:Crystallography, X-Ray; D004265:DNA Helicases / Q000737:chemistry; D004277:DNA, Single-Stranded / Q000737:chemistry*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D008958:Models, Molecular; D012329:RNA, Bacterial / Q000737:chemistry*
chemical_list: D064130:CRISPR-Associated Proteins; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D004265:DNA Helicases; C574631:ygcB protein, E coli