title: Structural basis for DNase activity of a conserved protein implicated in CRISPR-mediated genome defense.
abstract: Acquired immunity in prokaryotes is achieved by integrating short fragments of foreign nucleic acids into clustered regularly interspaced short palindromic repeats (CRISPRs). This nucleic acid-based immune system is mediated by a variable cassette of up to 45 protein families that represent distinct immune system subtypes. CRISPR-associated gene 1 (cas1) encodes the only universally conserved protein component of CRISPR immune systems, yet its function is unknown. Here we show that the Cas1 protein is a metal-dependent DNA-specific endonuclease that produces double-stranded DNA fragments of approximately 80 base pairs in length. The 2.2 A crystal structure of the Cas1 protein reveals a distinct fold and a conserved divalent metal ion-binding site. Mutation of metal ion-binding residues, chelation of metal ions, or metal-ion substitution inhibits Cas1-catalyzed DNA degradation. These results provide a foundation for understanding how Cas1 contributes to CRISPR function, perhaps as part of the machinery for processing foreign nucleic acids.
authors.affiliation: Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Blake
authors.initials: B
authors.lastname: Wiedenheft
authors.forename: Kaihong
authors.initials: K
authors.lastname: Zhou
authors.forename: Martin
authors.initials: M
authors.lastname: Jinek
authors.forename: Scott M
authors.initials: SM
authors.lastname: Coyle
authors.forename: Wendy
authors.initials: W
authors.lastname: Ma
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Doudna
mesh_terms: D000595:Amino Acid Sequence; D020029:Base Pairing; D001483:Base Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D003851:Deoxyribonucleases / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D016678:Genome; D016680:Genome, Bacterial; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011387:Prokaryotic Cells / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial; D011506:Proteins; D003851:Deoxyribonucleases