title: Conformational Control of Cascade Interference and Priming Activities in CRISPR Immunity.
abstract: During type I-E CRISPR-Cas immunity, the Cascade surveillance complex utilizes CRISPR-derived RNAs to target complementary invasive DNA for destruction. When invader mutation blocks this interference activity, Cascade instead triggers rapid primed adaptation against the invader. The molecular basis for this dual Cascade activity is poorly understood. Here we show that the conformation of the Cse1 subunit controls Cascade activity. Using FRET, we find that Cse1 exists in a dynamic equilibrium between "open" and "closed" conformations, and the extent to which the open conformation is favored directly correlates with the attenuation of interference and relative increase in priming activity upon target mutation. Additionally, the Cse1 L1 motif modulates Cascade activity by stabilizing the closed conformation. L1 mutations promote the open conformation and switch immune response from interference to priming. Our results demonstrate that Cascade conformation controls the functional outcome of target recognition, enabling tunable CRISPR immune response to combat invader evolution.
authors.affiliation: Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, Ames, IA 50011, USA.
authors.forename: Chaoyou
authors.initials: C
authors.lastname: Xue
authors.affiliation: Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, Ames, IA 50011, USA.
authors.forename: Natalie R
authors.initials: NR
authors.lastname: Whitis
authors.affiliation: Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, Ames, IA 50011, USA. Electronic address: sashital@iastate.edu.
authors.forename: Dipali G
authors.initials: DG
authors.lastname: Sashital
mesh_terms: D001665:Binding Sites; D064130:CRISPR-Associated Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D064113:CRISPR-Cas Systems / Q000276:immunology*; D002232:Carbocyanines / Q000737:chemistry; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D048168:Escherichia coli K12 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial; D009154:Mutation; D010957:Plasmids / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D017433:Protein Structure, Secondary; D013194:Staining and Labeling / Q000379:methods
chemical_list: D064130:CRISPR-Associated Proteins; D002232:Carbocyanines; C577974:CasB protein, E coli; C000605812:Cse1 protein, E coli; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; C089187:cyanine dye 3; C085321:cyanine dye 5; D004265:DNA Helicases; C574631:ygcB protein, E coli